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Boost.Interprocess"> 10<link rel="prev" href="synchronization_mechanisms.html" title="Synchronization mechanisms"> 11<link rel="next" href="allocators_containers.html" title="Allocators, containers and memory allocation algorithms"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="synchronization_mechanisms.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../interprocess.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="allocators_containers.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="interprocess.managed_memory_segments"></a><a class="link" href="managed_memory_segments.html" title="Managed Memory Segments">Managed Memory Segments</a> 29</h2></div></div></div> 30<div class="toc"><dl class="toc"> 31<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy">Making 32 Interprocess Data Communication Easy</a></span></dt> 33<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory">Managed 34 Shared Memory</a></span></dt> 35<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files">Managed 36 Mapped File</a></span></dt> 37<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features">Managed 38 Memory Segment Features</a></span></dt> 39<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features">Managed 40 Memory Segment Advanced Features</a></span></dt> 41<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer">Managed 42 Heap Memory And Managed External Buffer</a></span></dt> 43</dl></div> 44<div class="section"> 45<div class="titlepage"><div><div><h3 class="title"> 46<a name="interprocess.managed_memory_segments.making_ipc_easy"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy" title="Making Interprocess Data Communication Easy">Making 47 Interprocess Data Communication Easy</a> 48</h3></div></div></div> 49<div class="toc"><dl class="toc"> 50<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro">Introduction</a></span></dt> 51<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int">Declaration 52 of managed memory segment classes</a></span></dt> 53</dl></div> 54<div class="section"> 55<div class="titlepage"><div><div><h4 class="title"> 56<a name="interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segments_intro" title="Introduction">Introduction</a> 57</h4></div></div></div> 58<p> 59 As we have seen, <span class="bold"><strong>Boost.Interprocess</strong></span> offers 60 some basic classes to create shared memory objects and file mappings and 61 map those mappable classes to the process' address space. 62 </p> 63<p> 64 However, managing those memory segments is not not easy for non-trivial 65 tasks. A mapped region is a fixed-length memory buffer and creating and 66 destroying objects of any type dynamically, requires a lot of work, since 67 it would require programming a memory management algorithm to allocate 68 portions of that segment. Many times, we also want to associate names to 69 objects created in shared memory, so all the processes can find the object 70 using the name. 71 </p> 72<p> 73 <span class="bold"><strong>Boost.Interprocess</strong></span> offers 4 managed memory 74 segment classes: 75 </p> 76<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 77<li class="listitem"> 78 To manage a shared memory mapped region (<span class="bold"><strong>basic_managed_shared_memory</strong></span> 79 class). 80 </li> 81<li class="listitem"> 82 To manage a memory mapped file (<span class="bold"><strong>basic_managed_mapped_file</strong></span>). 83 </li> 84<li class="listitem"> 85 To manage a heap allocated (<code class="computeroutput"><span class="keyword">operator</span> 86 <span class="keyword">new</span></code>) memory buffer (<span class="bold"><strong>basic_managed_heap_memory</strong></span> class). 87 </li> 88<li class="listitem"> 89 To manage a user provided fixed size buffer (<span class="bold"><strong>basic_managed_external_buffer</strong></span> 90 class). 91 </li> 92</ul></div> 93<p> 94 The first two classes manage memory segments that can be shared between 95 processes. The third is useful to create complex data-bases to be sent 96 though other mechanisms like message queues to other processes. The fourth 97 class can manage any fixed size memory buffer. The first two classes will 98 be explained in the next two sections. <span class="bold"><strong>basic_managed_heap_memory</strong></span> 99 and <span class="bold"><strong>basic_managed_external_buffer</strong></span> will 100 be explained later. 101 </p> 102<p> 103 The most important services of a managed memory segment are: 104 </p> 105<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 106<li class="listitem"> 107 Dynamic allocation of portions of a memory the segment. 108 </li> 109<li class="listitem"> 110 Construction of C++ objects in the memory segment. These objects can 111 be anonymous or we can associate a name to them. 112 </li> 113<li class="listitem"> 114 Searching capabilities for named objects. 115 </li> 116<li class="listitem"> 117 Customization of many features: memory allocation algorithm, index 118 types or character types. 119 </li> 120<li class="listitem"> 121 Atomic constructions and destructions so that if the segment is shared 122 between two processes it's impossible to create two objects associated 123 with the same name, simplifying synchronization. 124 </li> 125</ul></div> 126</div> 127<div class="section"> 128<div class="titlepage"><div><div><h4 class="title"> 129<a name="interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.making_ipc_easy.managed_memory_segment_int" title="Declaration of managed memory segment classes">Declaration 130 of managed memory segment classes</a> 131</h4></div></div></div> 132<p> 133 All <span class="bold"><strong>Boost.Interprocess</strong></span> managed memory 134 segment classes are templatized classes that can be customized by the user: 135 </p> 136<pre class="programlisting"><span class="keyword">template</span> 137 <span class="special"><</span> 138 <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> 139 <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span> 140 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">IndexType</span> 141 <span class="special">></span> 142<span class="keyword">class</span> <span class="identifier">basic_managed_shared_memory</span> <span class="special">/</span> <span class="identifier">basic_managed_mapped_file</span> <span class="special">/</span> 143 <span class="identifier">basic_managed_heap_memory</span> <span class="special">/</span> <span class="identifier">basic_external_buffer</span><span class="special">;</span> 144</pre> 145<p> 146 These classes can be customized with the following template parameters: 147 </p> 148<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 149<li class="listitem"> 150 <span class="bold"><strong>CharType</strong></span> is the type of the character 151 that will be used to identify the created named objects (for example, 152 <span class="bold"><strong>char</strong></span> or <span class="bold"><strong>wchar_t</strong></span>) 153 </li> 154<li class="listitem"> 155 <span class="bold"><strong>MemoryAlgorithm</strong></span> is the memory algorithm 156 used to allocate portions of the segment (for example, rbtree_best_fit 157 ). The internal typedefs of the memory algorithm also define: 158 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 159<li class="listitem"> 160 The synchronization type (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">mutex_family</span></code>) 161 to be used in all allocation operations. This allows the use 162 of user-defined mutexes or avoiding internal locking (maybe code 163 will be externally synchronized by the user). 164 </li> 165<li class="listitem"> 166 The Pointer type (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">void_pointer</span></code>) 167 to be used by the memory allocation algorithm or additional helper 168 structures (like a map to maintain object/name associations). 169 All STL compatible allocators and containers to be used with 170 this managed memory segment will use this pointer type. The pointer 171 type will define if the managed memory segment can be mapped 172 between several processes. For example, if <code class="computeroutput"><span class="identifier">void_pointer</span></code> 173 is <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> we will be able to map the 174 managed segment in different base addresses in each process. 175 If <code class="computeroutput"><span class="identifier">void_pointer</span></code> 176 is <code class="computeroutput"><span class="keyword">void</span><span class="special">*</span></code> 177 only fixed address mapping could be used. 178 </li> 179<li class="listitem"> 180 See <a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_interprocess_alloc" title="Writing a new shared memory allocation algorithm">Writing 181 a new memory allocation algorithm</a> for more details about 182 memory algorithms. 183 </li> 184</ul></div> 185 </li> 186<li class="listitem"> 187 <span class="bold"><strong>IndexType</strong></span> is the type of index that 188 will be used to store the name-object association (for example, a map, 189 a hash-map, or an ordered vector). 190 </li> 191</ul></div> 192<p> 193 This way, we can use <code class="computeroutput"><span class="keyword">char</span></code> 194 or <code class="computeroutput"><span class="keyword">wchar_t</span></code> strings to identify 195 created C++ objects in the memory segment, we can plug new shared memory 196 allocation algorithms, and use the index type that is best suited to our 197 needs. 198 </p> 199</div> 200</div> 201<div class="section"> 202<div class="titlepage"><div><div><h3 class="title"> 203<a name="interprocess.managed_memory_segments.managed_shared_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory" title="Managed Shared Memory">Managed 204 Shared Memory</a> 205</h3></div></div></div> 206<div class="toc"><dl class="toc"> 207<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm">Common 208 Managed Shared Memory Classes</a></span></dt> 209<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories">Constructing 210 Managed Shared Memory</a></span></dt> 211<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm">Using 212 native windows shared memory</a></span></dt> 213<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm">Using 214 XSI (system V) shared memory</a></span></dt> 215</dl></div> 216<div class="section"> 217<div class="titlepage"><div><div><h4 class="title"> 218<a name="interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.managed_memory_common_shm" title="Common Managed Shared Memory Classes">Common 219 Managed Shared Memory Classes</a> 220</h4></div></div></div> 221<p> 222 As seen, <span class="bold"><strong>basic_managed_shared_memory</strong></span> offers 223 a great variety of customization. But for the average user, a common, default 224 shared memory named object creation is needed. Because of this, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the most common managed 225 shared memory specializations: 226 </p> 227<pre class="programlisting"><span class="comment">//!Defines a managed shared memory with c-strings as keys for named objects,</span> 228<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span> 229<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span> 230<span class="comment">//!and the default index type as the index.</span> 231<span class="comment">//!This class allows the shared memory to be mapped in different base</span> 232<span class="comment">//!in different processes</span> 233<span class="keyword">typedef</span> 234 <span class="identifier">basic_managed_shared_memory</span><span class="special"><</span><span class="keyword">char</span> 235 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span> 236 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/></span> 237 <span class="identifier">managed_shared_memory</span><span class="special">;</span> 238 239<span class="comment">//!Defines a managed shared memory with wide strings as keys for named objects,</span> 240<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span> 241<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span> 242<span class="comment">//!and the default index type as the index.</span> 243<span class="comment">//!This class allows the shared memory to be mapped in different base</span> 244<span class="comment">//!in different processes</span> 245<span class="keyword">typedef</span> 246 <span class="identifier">basic_managed_shared_memory</span><span class="special"><</span><span class="keyword">wchar_t</span> 247 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span> 248 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/></span> 249 <span class="identifier">wmanaged_shared_memory</span><span class="special">;</span> 250</pre> 251<p> 252 <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> allocates 253 objects in shared memory associated with a c-string and <code class="computeroutput"><span class="identifier">wmanaged_shared_memory</span></code> 254 allocates objects in shared memory associated with a wchar_t null terminated 255 string. Both define the pointer type as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> so they can be used to map the shared 256 memory at different base addresses in different processes. 257 </p> 258<p> 259 If the user wants to map the shared memory in the same address in all processes 260 and want to use raw pointers internally instead of offset pointers, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the following types: 261 </p> 262<pre class="programlisting"><span class="comment">//!Defines a managed shared memory with c-strings as keys for named objects,</span> 263<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span> 264<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span> 265<span class="comment">//!and the default index type as the index.</span> 266<span class="comment">//!This class allows the shared memory to be mapped in different base</span> 267<span class="comment">//!in different processes*/</span> 268<span class="keyword">typedef</span> <span class="identifier">basic_managed_shared_memory</span> 269 <span class="special"><</span><span class="keyword">char</span> 270 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span> 271 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/></span> 272<span class="identifier">fixed_managed_shared_memory</span><span class="special">;</span> 273 274<span class="comment">//!Defines a managed shared memory with wide strings as keys for named objects,</span> 275<span class="comment">//!the default memory algorithm (with process-shared mutexes,</span> 276<span class="comment">//!and offset_ptr as internal pointers) as memory allocation algorithm</span> 277<span class="comment">//!and the default index type as the index.</span> 278<span class="comment">//!This class allows the shared memory to be mapped in different base</span> 279<span class="comment">//!in different processes</span> 280<span class="keyword">typedef</span> <span class="identifier">basic_managed_shared_memory</span> 281 <span class="special"><</span><span class="keyword">wchar_t</span> 282 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">memory</span> <span class="identifier">algorithm</span> <span class="identifier">defining</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">as</span> <span class="identifier">void_pointer</span><span class="special">*/</span> 283 <span class="special">,/*</span><span class="identifier">Default</span> <span class="identifier">index</span> <span class="identifier">type</span><span class="special">*/></span> 284<span class="identifier">wfixed_managed_shared_memory</span><span class="special">;</span> 285</pre> 286</div> 287<div class="section"> 288<div class="titlepage"><div><div><h4 class="title"> 289<a name="interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.constructing_managed_shared_memories" title="Constructing Managed Shared Memory">Constructing 290 Managed Shared Memory</a> 291</h4></div></div></div> 292<p> 293 Managed shared memory is an advanced class that combines a shared memory 294 object and a mapped region that covers all the shared memory object. That 295 means that when we <span class="bold"><strong>create</strong></span> a new managed 296 shared memory: 297 </p> 298<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 299<li class="listitem"> 300 A new shared memory object is created. 301 </li> 302<li class="listitem"> 303 The whole shared memory object is mapped in the process' address space. 304 </li> 305<li class="listitem"> 306 Some helper objects are constructed (name-object index, internal synchronization 307 objects, internal variables...) in the mapped region to implement managed 308 memory segment features. 309 </li> 310</ul></div> 311<p> 312 When we <span class="bold"><strong>open</strong></span> a managed shared memory 313 </p> 314<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 315<li class="listitem"> 316 A shared memory object is opened. 317 </li> 318<li class="listitem"> 319 The whole shared memory object is mapped in the process' address space. 320 </li> 321</ul></div> 322<p> 323 To use a managed shared memory, you must include the following header: 324 </p> 325<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 326</pre> 327<pre class="programlisting"><span class="comment">//1. Creates a new shared memory object</span> 328<span class="comment">// called "MySharedMemory".</span> 329<span class="comment">//2. Maps the whole object to this</span> 330<span class="comment">// process' address space.</span> 331<span class="comment">//3. Constructs some objects in shared memory</span> 332<span class="comment">// to implement managed features.</span> 333<span class="comment">//!! If anything fails, throws interprocess_exception</span> 334<span class="comment">//</span> 335<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span> <span class="special">(</span> <span class="identifier">create_only</span> 336 <span class="special">,</span> <span class="string">"MySharedMemory"</span> <span class="comment">//Shared memory object name</span> 337 <span class="special">,</span> <span class="number">65536</span><span class="special">);</span> <span class="comment">//Shared memory object size in bytes</span> 338</pre> 339<pre class="programlisting"><span class="comment">//1. Opens a shared memory object</span> 340<span class="comment">// called "MySharedMemory".</span> 341<span class="comment">//2. Maps the whole object to this</span> 342<span class="comment">// process' address space.</span> 343<span class="comment">//3. Obtains pointers to constructed internal objects</span> 344<span class="comment">// to implement managed features.</span> 345<span class="comment">//!! If anything fails, throws interprocess_exception</span> 346<span class="comment">//</span> 347<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span> <span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">);//</span><span class="identifier">Shared</span> <span class="identifier">memory</span> <span class="identifier">object</span> <span class="identifier">name</span> 348</pre> 349<pre class="programlisting"><span class="comment">//1. If the segment was previously created</span> 350<span class="comment">// equivalent to "open_only" (size is ignored).</span> 351<span class="comment">//2. Otherwise, equivalent to "create_only"</span> 352<span class="comment">//!! If anything fails, throws interprocess_exception</span> 353<span class="comment">//</span> 354<span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span> <span class="special">(</span> <span class="identifier">open_or_create</span> 355 <span class="special">,</span> <span class="string">"MySharedMemory"</span> <span class="comment">//Shared memory object name</span> 356 <span class="special">,</span> <span class="number">65536</span><span class="special">);</span> <span class="comment">//Shared memory object size in bytes</span> 357</pre> 358<p> 359 When the <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> 360 object is destroyed, the shared memory object is automatically unmapped, 361 and all the resources are freed. To remove the shared memory object from 362 the system you must use the <code class="computeroutput"><span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span></code> 363 function. Shared memory object removing might fail if any process still 364 has the shared memory object mapped. 365 </p> 366<p> 367 The user can also map the managed shared memory in a fixed address. This 368 option is essential when using using <code class="computeroutput"><span class="identifier">fixed_managed_shared_memory</span></code>. 369 To do this, just add the mapping address as an extra parameter: 370 </p> 371<pre class="programlisting"><span class="identifier">fixed_managed_shared_memory</span> <span class="identifier">segment</span> <span class="special">(</span><span class="identifier">open_only</span> <span class="special">,</span><span class="string">"MyFixedAddressSharedMemory"</span> <span class="comment">//Shared memory object name</span> 372 <span class="special">,(</span><span class="keyword">void</span><span class="special">*)</span><span class="number">0x30000000</span> <span class="comment">//Mapping address</span> 373</pre> 374</div> 375<div class="section"> 376<div class="titlepage"><div><div><h4 class="title"> 377<a name="interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.windows_managed_memory_common_shm" title="Using native windows shared memory">Using 378 native windows shared memory</a> 379</h4></div></div></div> 380<p> 381 Windows users might also want to use native windows shared memory instead 382 of the portable <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_memory_object.html" title="Class shared_memory_object">shared_memory_object</a></code> 383 managed memory. This is achieved through the <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011618448.html" title="Class template basic_managed_windows_shared_memory">basic_managed_windows_shared_memory</a></code> 384 class. To use it just include: 385 </p> 386<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_windows_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 387</pre> 388<p> 389 This class has the same interface as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011676192.html" title="Class template basic_managed_shared_memory">basic_managed_shared_memory</a></code> 390 but uses native windows shared memory. Note that this managed class has 391 the same lifetime issues as the windows shared memory: when the last process 392 attached to the windows shared memory is detached from the memory (or ends/crashes) 393 the memory is destroyed. So there is no persistence support for windows 394 shared memory. 395 </p> 396<p> 397 To communicate between system services and user applications using <code class="computeroutput"><span class="identifier">managed_windows_shared_memory</span></code>, please 398 read the explanations given in chapter <a class="link" href="sharedmemorybetweenprocesses.html#interprocess.sharedmemorybetweenprocesses.sharedmemory.windows_shared_memory" title="Native windows shared memory">Native 399 windows shared memory</a>. 400 </p> 401</div> 402<div class="section"> 403<div class="titlepage"><div><div><h4 class="title"> 404<a name="interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_shared_memory.xsi_managed_memory_common_shm" title="Using XSI (system V) shared memory">Using 405 XSI (system V) shared memory</a> 406</h4></div></div></div> 407<p> 408 Unix users might also want to use XSI (system V) instead of the portable 409 <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_memory_object.html" title="Class shared_memory_object">shared_memory_object</a></code> 410 managed memory. This is achieved through the <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011569728.html" title="Class template basic_managed_xsi_shared_memory">basic_managed_xsi_shared_memory</a></code> 411 class. To use it just include: 412 </p> 413<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_xsi_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 414</pre> 415<p> 416 This class has nearly the same interface as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011676192.html" title="Class template basic_managed_shared_memory">basic_managed_shared_memory</a></code> 417 but uses XSI shared memory as backend. 418 </p> 419</div> 420<p> 421 For more information about managed XSI shared memory capabilities, see <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011569728.html" title="Class template basic_managed_xsi_shared_memory">basic_managed_xsi_shared_memory</a></code> 422 class reference. 423 </p> 424</div> 425<div class="section"> 426<div class="titlepage"><div><div><h3 class="title"> 427<a name="interprocess.managed_memory_segments.managed_mapped_files"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files" title="Managed Mapped File">Managed 428 Mapped File</a> 429</h3></div></div></div> 430<div class="toc"><dl class="toc"> 431<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile">Common 432 Managed Mapped Files</a></span></dt> 433<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files">Constructing 434 Managed Mapped Files</a></span></dt> 435</dl></div> 436<div class="section"> 437<div class="titlepage"><div><div><h4 class="title"> 438<a name="interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.managed_memory_common_mfile" title="Common Managed Mapped Files">Common 439 Managed Mapped Files</a> 440</h4></div></div></div> 441<p> 442 As seen, <span class="bold"><strong>basic_managed_mapped_file</strong></span> offers 443 a great variety of customization. But for the average user, a common, default 444 shared memory named object creation is needed. Because of this, <span class="bold"><strong>Boost.Interprocess</strong></span> defines the most common managed 445 mapped file specializations: 446 </p> 447<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span> 448<span class="comment">//All objects are constructed in the memory-mapped file</span> 449<span class="comment">// Names are c-strings,</span> 450<span class="comment">// Default memory management algorithm(rbtree_best_fit with no mutexes)</span> 451<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 452<span class="keyword">typedef</span> <span class="identifier">basic_managed_mapped_file</span> <span class="special"><</span> 453 <span class="keyword">char</span><span class="special">,</span> 454 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">>,</span> 455 <span class="identifier">flat_map_index</span> 456 <span class="special">></span> <span class="identifier">managed_mapped_file</span><span class="special">;</span> 457 458<span class="comment">//Named object creation managed memory segment</span> 459<span class="comment">//All objects are constructed in the memory-mapped file</span> 460<span class="comment">// Names are wide-strings,</span> 461<span class="comment">// Default memory management algorithm(rbtree_best_fit with no mutexes)</span> 462<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 463<span class="keyword">typedef</span> <span class="identifier">basic_managed_mapped_file</span><span class="special"><</span> 464 <span class="keyword">wchar_t</span><span class="special">,</span> 465 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">>,</span> 466 <span class="identifier">flat_map_index</span> 467 <span class="special">></span> <span class="identifier">wmanaged_mapped_file</span><span class="special">;</span> 468</pre> 469<p> 470 <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code> allocates 471 objects in a memory mapped files associated with a c-string and <code class="computeroutput"><span class="identifier">wmanaged_mapped_file</span></code> allocates objects 472 in a memory mapped file associated with a wchar_t null terminated string. 473 Both define the pointer type as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> so they can be used to map the file 474 at different base addresses in different processes. 475 </p> 476</div> 477<div class="section"> 478<div class="titlepage"><div><div><h4 class="title"> 479<a name="interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_mapped_files.constructing_managed_mapped_files" title="Constructing Managed Mapped Files">Constructing 480 Managed Mapped Files</a> 481</h4></div></div></div> 482<p> 483 Managed mapped file is an advanced class that combines a file and a mapped 484 region that covers all the file. That means that when we <span class="bold"><strong>create</strong></span> 485 a new managed mapped file: 486 </p> 487<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 488<li class="listitem"> 489 A new file is created. 490 </li> 491<li class="listitem"> 492 The whole file is mapped in the process' address space. 493 </li> 494<li class="listitem"> 495 Some helper objects are constructed (name-object index, internal synchronization 496 objects, internal variables...) in the mapped region to implement managed 497 memory segment features. 498 </li> 499</ul></div> 500<p> 501 When we <span class="bold"><strong>open</strong></span> a managed mapped file 502 </p> 503<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 504<li class="listitem"> 505 A file is opened. 506 </li> 507<li class="listitem"> 508 The whole file is mapped in the process' address space. 509 </li> 510</ul></div> 511<p> 512 To use a managed mapped file, you must include the following header: 513 </p> 514<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 515</pre> 516<pre class="programlisting"><span class="comment">//1. Creates a new file</span> 517<span class="comment">// called "MyMappedFile".</span> 518<span class="comment">//2. Maps the whole file to this</span> 519<span class="comment">// process' address space.</span> 520<span class="comment">//3. Constructs some objects in the memory mapped</span> 521<span class="comment">// file to implement managed features.</span> 522<span class="comment">//!! If anything fails, throws interprocess_exception</span> 523<span class="comment">//</span> 524<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span> <span class="special">(</span> <span class="identifier">create_only</span> 525 <span class="special">,</span> <span class="string">"MyMappedFile"</span> <span class="comment">//Mapped file name</span> 526 <span class="special">,</span> <span class="number">65536</span><span class="special">);</span> <span class="comment">//Mapped file size</span> 527</pre> 528<pre class="programlisting"><span class="comment">//1. Opens a file</span> 529<span class="comment">// called "MyMappedFile".</span> 530<span class="comment">//2. Maps the whole file to this</span> 531<span class="comment">// process' address space.</span> 532<span class="comment">//3. Obtains pointers to constructed internal objects</span> 533<span class="comment">// to implement managed features.</span> 534<span class="comment">//!! If anything fails, throws interprocess_exception</span> 535<span class="comment">//</span> 536<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span> <span class="special">(</span> <span class="identifier">open_only</span> 537 <span class="special">,</span> <span class="string">"MyMappedFile"</span><span class="special">);</span> <span class="comment">//Mapped file name</span> 538</pre> 539<pre class="programlisting"><span class="comment">//1. If the file was previously created</span> 540<span class="comment">// equivalent to "open_only".</span> 541<span class="comment">//2. Otherwise, equivalent to "open_only" (size is ignored)</span> 542<span class="comment">//</span> 543<span class="comment">//!! If anything fails, throws interprocess_exception</span> 544<span class="comment">//</span> 545<span class="identifier">managed_mapped_file</span> <span class="identifier">mfile</span> <span class="special">(</span><span class="identifier">open_or_create</span> 546 <span class="special">,</span> <span class="string">"MyMappedFile"</span> <span class="comment">//Mapped file name</span> 547 <span class="special">,</span> <span class="number">65536</span><span class="special">);</span> <span class="comment">//Mapped file size</span> 548</pre> 549<p> 550 When the <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code> 551 object is destroyed, the file is automatically unmapped, and all the resources 552 are freed. To remove the file from the filesystem you could use standard 553 C <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">remove</span></code> or <span class="bold"><strong>Boost.Filesystem</strong></span>'s 554 <code class="computeroutput"><span class="identifier">remove</span><span class="special">()</span></code> 555 functions, but file removing might fail if any process still has the file 556 mapped in memory or the file is open by any process. 557 </p> 558<p> 559 To obtain a more portable behaviour, use <code class="computeroutput"><span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*)</span></code> 560 operation, which will remove the file even if it's being mapped. However, 561 removal will fail in some OS systems if the file (eg. by C++ file streams) 562 and no delete share permission was granted to the file. But in most common 563 cases <code class="computeroutput"><span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span></code> is portable enough. 564 </p> 565</div> 566<p> 567 For more information about managed mapped file capabilities, see <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_managed_mapped_file.html" title="Class template basic_managed_mapped_file">basic_managed_mapped_file</a></code> 568 class reference. 569 </p> 570</div> 571<div class="section"> 572<div class="titlepage"><div><div><h3 class="title"> 573<a name="interprocess.managed_memory_segments.managed_memory_segment_features"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features" title="Managed Memory Segment Features">Managed 574 Memory Segment Features</a> 575</h3></div></div></div> 576<div class="toc"><dl class="toc"> 577<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate">Allocating 578 fragments of a managed memory segment</a></span></dt> 579<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset">Obtaining 580 handles to identify data</a></span></dt> 581<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types">Object 582 construction function family</a></span></dt> 583<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.anonymous">Anonymous 584 instance construction</a></span></dt> 585<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique">Unique 586 instance construction</a></span></dt> 587<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.synchronization">Synchronization 588 guarantees</a></span></dt> 589<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.index_types">Index 590 types for name/object mappings</a></span></dt> 591<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager">Segment 592 Manager</a></span></dt> 593<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information">Obtaining 594 information about a constructed object</a></span></dt> 595<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func">Executing 596 an object function atomically</a></span></dt> 597</dl></div> 598<p> 599 The following features are common to all managed memory segment classes, 600 but we will use managed shared memory in our examples. We can do the same 601 with memory mapped files or other managed memory segment classes. 602 </p> 603<div class="section"> 604<div class="titlepage"><div><div><h4 class="title"> 605<a name="interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocate_deallocate" title="Allocating fragments of a managed memory segment">Allocating 606 fragments of a managed memory segment</a> 607</h4></div></div></div> 608<p> 609 If a basic raw-byte allocation is needed from a managed memory segment, 610 (for example, a managed shared memory), to implement top-level interprocess 611 communications, this class offers <span class="bold"><strong>allocate</strong></span> 612 and <span class="bold"><strong>deallocate</strong></span> functions. The allocation 613 function comes with throwing and no throwing versions. Throwing version 614 throws boost::interprocess::bad_alloc (which derives from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bad_alloc</span></code>) if there is no more memory 615 and the non-throwing version returns 0 pointer. 616 </p> 617<p> 618</p> 619<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 620 621<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 622<span class="special">{</span> 623 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 624 625 <span class="comment">//Remove shared memory on construction and destruction</span> 626 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 627 <span class="special">{</span> 628 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 629 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 630 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 631 632 <span class="comment">//Managed memory segment that allocates portions of a shared memory</span> 633 <span class="comment">//segment with the default management algorithm</span> 634 <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 635 636 <span class="comment">//Allocate 100 bytes of memory from segment, throwing version</span> 637 <span class="keyword">void</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">100</span><span class="special">);</span> 638 639 <span class="comment">//Deallocate it</span> 640 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 641 642 <span class="comment">//Non throwing version</span> 643 <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">);</span> 644 645 <span class="comment">//Deallocate it</span> 646 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 647 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 648<span class="special">}</span> 649</pre> 650<p> 651 </p> 652</div> 653<div class="section"> 654<div class="titlepage"><div><div><h4 class="title"> 655<a name="interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.segment_offset" title="Obtaining handles to identify data">Obtaining 656 handles to identify data</a> 657</h4></div></div></div> 658<p> 659 The class also offers conversions between absolute addresses that belong 660 to a managed memory segment and a handle that can be passed using any interprocess 661 mechanism. That handle can be transformed again to an absolute address 662 using a managed memory segment that also contains that object. Handles 663 can be used as keys between processes to identify allocated portions of 664 a managed memory segment or objects constructed in the managed segment. 665 </p> 666<pre class="programlisting"><span class="comment">//Process A obtains the offset of the address</span> 667<span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">handle</span> <span class="identifier">handle</span> <span class="special">=</span> 668 <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_handle_from_address</span><span class="special">(</span><span class="identifier">processA_address</span><span class="special">);</span> 669 670<span class="comment">//Process A sends this address using any mechanism to process B</span> 671 672<span class="comment">//Process B obtains the handle and transforms it again to an address</span> 673<span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">handle</span> <span class="identifier">handle</span> <span class="special">=</span> <span class="special">...</span> 674<span class="keyword">void</span> <span class="special">*</span> <span class="identifier">processB_address</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_address_from_handle</span><span class="special">(</span><span class="identifier">handle</span><span class="special">);</span> 675</pre> 676</div> 677<div class="section"> 678<div class="titlepage"><div><div><h4 class="title"> 679<a name="interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.allocation_types" title="Object construction function family">Object 680 construction function family</a> 681</h4></div></div></div> 682<p> 683 When constructing objects in a managed memory segment (managed shared memory, 684 managed mapped files...) associated with a name, the user has a varied 685 object construction family to "construct" or to "construct 686 if not found". <span class="bold"><strong>Boost.Interprocess</strong></span> 687 can construct a single object or an array of objects. The array can be 688 constructed with the same parameters for all objects or we can define each 689 parameter from a list of iterators: 690 </p> 691<pre class="programlisting"><span class="comment">//!Allocates and constructs an object of type MyType (throwing version)</span> 692<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 693 694<span class="comment">//!Allocates and constructs an array of objects of type MyType (throwing version)</span> 695<span class="comment">//!Each object receives the same parameters (par1, par2, ...)</span> 696<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 697 698<span class="comment">//!Tries to find a previously created object. If not present, allocates</span> 699<span class="comment">//!and constructs an object of type MyType (throwing version)</span> 700<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 701 702<span class="comment">//!Tries to find a previously created object. If not present, allocates and</span> 703<span class="comment">//!constructs an array of objects of type MyType (throwing version). Each object</span> 704<span class="comment">//!receives the same parameters (par1, par2, ...)</span> 705<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 706 707<span class="comment">//!Allocates and constructs an array of objects of type MyType (throwing version)</span> 708<span class="comment">//!Each object receives parameters returned with the expression (*it1++, *it2++,... )</span> 709<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct_it</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">it1</span><span class="special">,</span> <span class="identifier">it2</span><span class="special">...);</span> 710 711<span class="comment">//!Tries to find a previously created object. If not present, allocates and constructs</span> 712<span class="comment">//!an array of objects of type MyType (throwing version). Each object receives</span> 713<span class="comment">//!parameters returned with the expression (*it1++, *it2++,... )</span> 714<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find_or_construct_it</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">it1</span><span class="special">,</span> <span class="identifier">it2</span><span class="special">...);</span> 715 716<span class="comment">//!Tries to find a previously created object. Returns a pointer to the object and the</span> 717<span class="comment">//!count (if it is not an array, returns 1). If not present, the returned pointer is 0</span> 718<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">MyType</span> <span class="special">*,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">);</span> 719 720<span class="comment">//!Destroys the created object, returns false if not present</span> 721<span class="keyword">bool</span> <span class="identifier">destroyed</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">);</span> 722 723<span class="comment">//!Destroys the created object via pointer</span> 724<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 725</pre> 726<p> 727 All these functions have a non-throwing version, that is invoked with an 728 additional parameter std::nothrow. For example, for simple object construction: 729 </p> 730<pre class="programlisting"><span class="comment">//!Allocates and constructs an object of type MyType (no throwing version)</span> 731<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 732</pre> 733</div> 734<div class="section"> 735<div class="titlepage"><div><div><h4 class="title"> 736<a name="interprocess.managed_memory_segments.managed_memory_segment_features.anonymous"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.anonymous" title="Anonymous instance construction">Anonymous 737 instance construction</a> 738</h4></div></div></div> 739<p> 740 Sometimes, the user doesn't want to create class objects associated with 741 a name. For this purpose, <span class="bold"><strong>Boost.Interprocess</strong></span> 742 can create anonymous objects in a managed memory segment. All named object 743 construction functions are available to construct anonymous objects. To 744 allocate an anonymous objects, the user must use "boost::interprocess::anonymous_instance" 745 name instead of a normal name: 746 </p> 747<pre class="programlisting"><span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">anonymous_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 748 749<span class="comment">//Other construct variants can also be used (including non-throwing ones)</span> 750<span class="special">...</span> 751 752<span class="comment">//We can only destroy the anonymous object via pointer</span> 753<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 754</pre> 755<p> 756 Find functions have no sense here, since anonymous objects have no name. 757 We can only destroy the anonymous object via pointer. 758 </p> 759</div> 760<div class="section"> 761<div class="titlepage"><div><div><h4 class="title"> 762<a name="interprocess.managed_memory_segments.managed_memory_segment_features.unique"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique" title="Unique instance construction">Unique 763 instance construction</a> 764</h4></div></div></div> 765<p> 766 Sometimes, the user wants to emulate a singleton in a managed memory segment. 767 Obviously, as the managed memory segment is constructed at run-time, the 768 user must construct and destroy this object explicitly. But how can the 769 user be sure that the object is the only object of its type in the managed 770 memory segment? This can be emulated using a named object and checking 771 if it is present before trying to create one, but all processes must agree 772 in the object's name, that can also conflict with other existing names. 773 </p> 774<p> 775 To solve this, <span class="bold"><strong>Boost.Interprocess</strong></span> offers 776 a "unique object" creation in a managed memory segment. Only 777 one instance of a class can be created in a managed memory segment using 778 this "unique object" service (you can create more named objects 779 of this class, though) so it makes easier the emulation of singleton-like 780 objects across processes, for example, to design pooled, shared memory 781 allocators. The object can be searched using the type of the class as a 782 key. 783 </p> 784<pre class="programlisting"><span class="comment">// Construct</span> 785<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">unique_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 786 787<span class="comment">// Find it</span> 788<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">MyType</span> <span class="special">*,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">unique_instance</span><span class="special">);</span> 789 790<span class="comment">// Destroy it</span> 791<span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">unique_instance</span><span class="special">);</span> 792 793<span class="comment">// Other construct and find variants can also be used (including non-throwing ones)</span> 794<span class="comment">//...</span> 795</pre> 796<pre class="programlisting"><span class="comment">// We can also destroy the unique object via pointer</span> 797<span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_memory_segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">unique_instance</span><span class="special">)</span> <span class="special">(</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 798<span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 799</pre> 800<p> 801 The find function obtains a pointer to the only object of type T that can 802 be created using this "unique instance" mechanism. 803 </p> 804</div> 805<div class="section"> 806<div class="titlepage"><div><div><h4 class="title"> 807<a name="interprocess.managed_memory_segments.managed_memory_segment_features.synchronization"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.synchronization" title="Synchronization guarantees">Synchronization 808 guarantees</a> 809</h4></div></div></div> 810<p> 811 One of the features of named/unique allocations/searches/destructions is 812 that they are <span class="bold"><strong>atomic</strong></span>. Named allocations 813 use the recursive synchronization scheme defined by the internal <code class="computeroutput"><span class="identifier">mutex_family</span></code> typedef defined of the memory 814 allocation algorithm template parameter (<code class="computeroutput"><span class="identifier">MemoryAlgorithm</span></code>). 815 That is, the mutex type used to synchronize named/unique allocations is 816 defined by the <code class="computeroutput"><span class="identifier">MemoryAlgorithm</span><span class="special">::</span><span class="identifier">mutex_family</span><span class="special">::</span><span class="identifier">recursive_mutex_type</span></code> 817 type. For shared memory, and memory mapped file based managed segments 818 this recursive mutex is defined as <code class="computeroutput"><a class="link" href="../boost/interprocess/interpro_idm45304010361200.html" title="Class interprocess_recursive_mutex">interprocess_recursive_mutex</a></code>. 819 </p> 820<p> 821 If two processes can call: 822 </p> 823<pre class="programlisting"><span class="identifier">MyType</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">find_or_construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"Name"</span><span class="special">)[</span><span class="identifier">count</span><span class="special">](</span><span class="identifier">par1</span><span class="special">,</span> <span class="identifier">par2</span><span class="special">...);</span> 824</pre> 825<p> 826 at the same time, but only one process will create the object and the other 827 will obtain a pointer to the created object. 828 </p> 829<p> 830 Raw allocation using <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code> can be called also safely while executing 831 named/anonymous/unique allocations, just like when programming a multithreaded 832 application inserting an object in a mutex-protected map does not block 833 other threads from calling new[] while the map thread is searching the 834 place where it has to insert the new object. The synchronization does happen 835 once the map finds the correct place and it has to allocate raw memory 836 to construct the new value. 837 </p> 838<p> 839 This means that if we are creating or searching for a lot of named objects, 840 we only block creation/searches from other processes but we don't block 841 another process if that process is inserting elements in a shared memory 842 vector. 843 </p> 844</div> 845<div class="section"> 846<div class="titlepage"><div><div><h4 class="title"> 847<a name="interprocess.managed_memory_segments.managed_memory_segment_features.index_types"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.index_types" title="Index types for name/object mappings">Index 848 types for name/object mappings</a> 849</h4></div></div></div> 850<p> 851 As seen, managed memory segments, when creating named objects, store the 852 name/object association in an index. The index is a map with the name of 853 the object as a key and a pointer to the object as the mapped type. The 854 default specializations, <span class="bold"><strong>managed_shared_memory</strong></span> 855 and <span class="bold"><strong>wmanaged_shared_memory</strong></span>, use <span class="bold"><strong>flat_map_index</strong></span> as the index type. 856 </p> 857<p> 858 Each index has its own characteristics, like search-time, insertion time, 859 deletion time, memory use, and memory allocation patterns. <span class="bold"><strong>Boost.Interprocess</strong></span> 860 offers 3 index types right now: 861 </p> 862<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 863<li class="listitem"> 864 <span class="bold"><strong>boost::interprocess::flat_map_index flat_map_index</strong></span>: 865 Based on boost::interprocess::flat_map, an ordered vector similar to 866 Loki library's AssocVector class, offers great search time and minimum 867 memory use. But the vector must be reallocated when is full, so all 868 data must be copied to the new buffer. Ideal when insertions are mainly 869 in initialization time and in run-time we just need searches. 870 </li> 871<li class="listitem"> 872 <span class="bold"><strong>boost::interprocess::map_index map_index</strong></span>: 873 Based on boost::interprocess::map, a managed memory ready version of 874 std::map. Since it's a node based container, it has no reallocations, 875 the tree must be just rebalanced sometimes. Offers equilibrated insertion/deletion/search 876 times with more overhead per node comparing to <span class="bold"><strong>boost::interprocess::flat_map_index</strong></span>. 877 Ideal when searches/insertions/deletions are in random order. 878 </li> 879<li class="listitem"> 880 <span class="bold"><strong>boost::interprocess::null_index null_index</strong></span>: 881 This index is for people using a managed memory segment just for raw 882 memory buffer allocations and they don't make use of named/unique allocations. 883 This class is just empty and saves some space and compilation time. 884 If you try to use named object creation with a managed memory segment 885 using this index, you will get a compilation error. 886 </li> 887</ul></div> 888<p> 889 As an example, if we want to define new managed shared memory class using 890 <span class="bold"><strong>boost::interprocess::map</strong></span> as the index 891 type we just must specify [boost::interprocess::map_index map_index] as 892 a template parameter: 893 </p> 894<pre class="programlisting"><span class="comment">//This managed memory segment can allocate objects with:</span> 895<span class="comment">// -> a wchar_t string as key</span> 896<span class="comment">// -> boost::interprocess::rbtree_best_fit with process-shared mutexes</span> 897<span class="comment">// as memory allocation algorithm.</span> 898<span class="comment">// -> boost::interprocess::map<...> as the index to store name/object mappings</span> 899<span class="comment">//</span> 900<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">basic_managed_shared_memory</span> 901 <span class="special"><</span> <span class="keyword">wchar_t</span> 902 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">></span> 903 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">map_index</span> 904 <span class="special">></span> <span class="identifier">my_managed_shared_memory</span><span class="special">;</span> 905</pre> 906<p> 907 <span class="bold"><strong>Boost.Interprocess</strong></span> plans to offer an 908 <span class="bold"><strong>unordered_map</strong></span> based index as soon as this 909 container is included in Boost. If these indexes are not enough for you, 910 you can define your own index type. To know how to do this, go to <a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_indexes" title="Building custom indexes">Building 911 custom indexes</a> section. 912 </p> 913</div> 914<div class="section"> 915<div class="titlepage"><div><div><h4 class="title"> 916<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_segment_manager" title="Segment Manager">Segment 917 Manager</a> 918</h4></div></div></div> 919<p> 920 All <span class="bold"><strong>Boost.Interprocess</strong></span> managed memory 921 segment classes construct in their respective memory segments (shared memory, 922 memory mapped files, heap memory...) some structures to implement the memory 923 management algorithm, named allocations, synchronization objects... All 924 these objects are encapsulated in a single object called <span class="bold"><strong>segment 925 manager</strong></span>. A managed memory mapped file and a managed shared memory 926 use the same <span class="bold"><strong>segment manager</strong></span> to implement 927 all managed memory segment features, due to the fact that a <span class="bold"><strong>segment 928 manager</strong></span> is a class that manages a fixed size memory buffer. 929 Since both shared memory or memory mapped files are accessed though a mapped 930 region, and a mapped region is a fixed size memory buffer, a single <span class="bold"><strong>segment manager</strong></span> class can manage several managed 931 memory segment types. 932 </p> 933<p> 934 Some <span class="bold"><strong>Boost.Interprocess</strong></span> classes require 935 a pointer to the segment manager in their constructors, and the segment 936 manager can be obtained from any managed memory segment using <code class="computeroutput"><span class="identifier">get_segment_manager</span></code> member: 937 </p> 938<pre class="programlisting"><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">seg_manager</span> <span class="special">=</span> 939 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">();</span> 940</pre> 941</div> 942<div class="section"> 943<div class="titlepage"><div><div><h4 class="title"> 944<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_information" title="Obtaining information about a constructed object">Obtaining 945 information about a constructed object</a> 946</h4></div></div></div> 947<p> 948 Once an object is constructed using <code class="computeroutput"><span class="identifier">construct</span><span class="special"><></span></code> function family, the programmer 949 can obtain information about the object using a pointer to the object. 950 The programmer can obtain the following information: 951 </p> 952<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 953<li class="listitem"> 954 Name of the object: If it's a named instance, the name used in the 955 construction function is returned, otherwise 0 is returned. 956 </li> 957<li class="listitem"> 958 Length of the object: Returns the number of elements of the object 959 (1 if it's a single value, >=1 if it's an array). 960 </li> 961<li class="listitem"> 962 The type of construction: Whether the object was constructed using 963 a named, unique or anonymous construction. 964 </li> 965</ul></div> 966<p> 967 Here is an example showing this functionality: 968 </p> 969<p> 970</p> 971<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 972<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 973<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstring</span><span class="special">></span> 974 975<span class="keyword">class</span> <span class="identifier">my_class</span> 976<span class="special">{</span> 977 <span class="comment">//...</span> 978<span class="special">};</span> 979 980<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 981<span class="special">{</span> 982 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 983 984 <span class="comment">//Remove shared memory on construction and destruction</span> 985 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 986 <span class="special">{</span> 987 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 988 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 989 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 990 991 <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">*</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">));</span> 992 993 <span class="comment">//Construct objects</span> 994 <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">named_object</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="string">"Object name"</span><span class="special">)[</span><span class="number">1</span><span class="special">]();</span> 995 <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">unique_object</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="identifier">unique_instance</span><span class="special">)[</span><span class="number">2</span><span class="special">]();</span> 996 <span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">anon_object</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="identifier">anonymous_instance</span><span class="special">)[</span><span class="number">3</span><span class="special">]();</span> 997 998 <span class="comment">//Now test "get_instance_name" function.</span> 999 <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">),</span> <span class="string">"Object name"</span><span class="special">));</span> 1000 <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">),</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">my_class</span><span class="special">).</span><span class="identifier">name</span><span class="special">()));</span> 1001 <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_name</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span> 1002 1003 <span class="comment">//Now test "get_instance_type" function.</span> 1004 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">named_type</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">));</span> 1005 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_type</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">));</span> 1006 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">anonymous_type</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_type</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span> 1007 1008 <span class="comment">//Now test "get_instance_length" function.</span> 1009 <span class="identifier">assert</span><span class="special">(</span><span class="number">1</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">));</span> 1010 <span class="identifier">assert</span><span class="special">(</span><span class="number">2</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">));</span> 1011 <span class="identifier">assert</span><span class="special">(</span><span class="number">3</span> <span class="special">==</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">get_instance_length</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">));</span> 1012 1013 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">named_object</span><span class="special">);</span> 1014 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_object</span><span class="special">);</span> 1015 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">anon_object</span><span class="special">);</span> 1016 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1017<span class="special">}</span> 1018</pre> 1019<p> 1020 </p> 1021</div> 1022<div class="section"> 1023<div class="titlepage"><div><div><h4 class="title"> 1024<a name="interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.managed_memory_segment_atomic_func" title="Executing an object function atomically">Executing 1025 an object function atomically</a> 1026</h4></div></div></div> 1027<p> 1028 Sometimes the programmer must execute some code, and needs to execute it 1029 with the guarantee that no other process or thread will create or destroy 1030 any named, unique or anonymous object while executing the functor. A user 1031 might want to create several named objects and initialize them, but those 1032 objects should be available for the rest of processes at once. 1033 </p> 1034<p> 1035 To achieve this, the programmer can use the <code class="computeroutput"><span class="identifier">atomic_func</span><span class="special">()</span></code> function offered by managed classes: 1036 </p> 1037<pre class="programlisting"><span class="comment">//This object function will create several named objects</span> 1038<span class="identifier">create_several_objects_func</span> <span class="identifier">func</span><span class="special">(/**/);</span> 1039 1040<span class="comment">//While executing the function, no other process will be</span> 1041<span class="comment">//able to create or destroy objects</span> 1042<span class="identifier">managed_memory</span><span class="special">.</span><span class="identifier">atomic_func</span><span class="special">(</span><span class="identifier">func</span><span class="special">);</span> 1043</pre> 1044<p> 1045 Note that <code class="computeroutput"><span class="identifier">atomic_func</span></code> does 1046 not prevent other processes from allocating raw memory or executing member 1047 functions for already constructed objects (e.g.: another process might 1048 be pushing elements into a vector placed in the segment). The atomic function 1049 only blocks named, unique and anonymous creation, search and destruction 1050 (concurrent calls to <code class="computeroutput"><span class="identifier">construct</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">find</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">destroy</span><span class="special"><></span></code>...) from other processes. 1051 </p> 1052</div> 1053</div> 1054<div class="section"> 1055<div class="titlepage"><div><div><h3 class="title"> 1056<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features" title="Managed Memory Segment Advanced Features">Managed 1057 Memory Segment Advanced Features</a> 1058</h3></div></div></div> 1059<div class="toc"><dl class="toc"> 1060<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information">Obtaining 1061 information about the managed segment</a></span></dt> 1062<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory">Growing 1063 managed segments</a></span></dt> 1064<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions">Advanced 1065 index functions</a></span></dt> 1066<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned">Allocating 1067 aligned memory portions</a></span></dt> 1068<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations">Multiple 1069 allocation functions</a></span></dt> 1070<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place">Expand 1071 in place memory allocation</a></span></dt> 1072<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only">Opening 1073 managed shared memory and mapped files with Copy On Write or Read Only modes</a></span></dt> 1074</dl></div> 1075<div class="section"> 1076<div class="titlepage"><div><div><h4 class="title"> 1077<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_information" title="Obtaining information about the managed segment">Obtaining 1078 information about the managed segment</a> 1079</h4></div></div></div> 1080<p> 1081 These functions are available to obtain information about the managed memory 1082 segments: 1083 </p> 1084<p> 1085 Obtain the size of the memory segment: 1086 </p> 1087<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">();</span> 1088</pre> 1089<p> 1090 Obtain the number of free bytes of the segment: 1091 </p> 1092<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span> 1093</pre> 1094<p> 1095 Clear to zero the free memory: 1096 </p> 1097<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">zero_free_memory</span><span class="special">();</span> 1098</pre> 1099<p> 1100 Know if all memory has been deallocated, false otherwise: 1101 </p> 1102<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">all_memory_deallocated</span><span class="special">();</span> 1103</pre> 1104<p> 1105 Test internal structures of the managed segment. Returns true if no errors 1106 are detected: 1107 </p> 1108<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">check_sanity</span><span class="special">();</span> 1109</pre> 1110<p> 1111 Obtain the number of named and unique objects allocated in the segment: 1112 </p> 1113<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_num_named_objects</span><span class="special">();</span> 1114<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_num_unique_objects</span><span class="special">();</span> 1115</pre> 1116</div> 1117<div class="section"> 1118<div class="titlepage"><div><div><h4 class="title"> 1119<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.growing_managed_memory" title="Growing managed segments">Growing 1120 managed segments</a> 1121</h4></div></div></div> 1122<p> 1123 Once a managed segment is created the managed segment can't be grown. The 1124 limitation is not easily solvable: every process attached to the managed 1125 segment would need to be stopped, notified of the new size, they would 1126 need to remap the managed segment and continue working. Nearly impossible 1127 to achieve with a user-level library without the help of the operating 1128 system kernel. 1129 </p> 1130<p> 1131 On the other hand, <span class="bold"><strong>Boost.Interprocess</strong></span> 1132 offers off-line segment growing. What does this mean? That the segment 1133 can be grown if no process has mapped the managed segment. If the application 1134 can find a moment where no process is attached it can grow or shrink to 1135 fit the managed segment. 1136 </p> 1137<p> 1138 Here we have an example showing how to grow and shrink to fit <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_shared_memory.html" title="Type definition managed_shared_memory">managed_shared_memory</a></code>: 1139 </p> 1140<p> 1141</p> 1142<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1143<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1144<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 1145 1146<span class="keyword">class</span> <span class="identifier">MyClass</span> 1147<span class="special">{</span> 1148 <span class="comment">//...</span> 1149<span class="special">};</span> 1150 1151<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 1152<span class="special">{</span> 1153 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 1154 <span class="comment">//Remove shared memory on construction and destruction</span> 1155 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1156 <span class="special">{</span> 1157 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1158 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1159 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1160 1161 <span class="special">{</span> 1162 <span class="comment">//Create a managed shared memory</span> 1163 <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">1000</span><span class="special">);</span> 1164 1165 <span class="comment">//Check size</span> 1166 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1000</span><span class="special">);</span> 1167 <span class="comment">//Construct a named object</span> 1168 <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>(</span><span class="string">"MyClass"</span><span class="special">)();</span> 1169 <span class="comment">//The managed segment is unmapped here</span> 1170 <span class="special">}</span> 1171 <span class="special">{</span> 1172 <span class="comment">//Now that the segment is not mapped grow it adding extra 500 bytes</span> 1173 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">grow</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">500</span><span class="special">);</span> 1174 1175 <span class="comment">//Map it again</span> 1176 <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">);</span> 1177 <span class="comment">//Check size</span> 1178 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1500</span><span class="special">);</span> 1179 <span class="comment">//Check "MyClass" is still there</span> 1180 <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>(</span><span class="string">"MyClass"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span> 1181 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myclass</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 1182 <span class="comment">//The managed segment is unmapped here</span> 1183 <span class="special">}</span> 1184 <span class="special">{</span> 1185 <span class="comment">//Now minimize the size of the segment</span> 1186 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">shrink_to_fit</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> 1187 1188 <span class="comment">//Map it again</span> 1189 <span class="identifier">managed_shared_memory</span> <span class="identifier">shm</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">);</span> 1190 <span class="comment">//Check size</span> 1191 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special"><</span> <span class="number">1000</span><span class="special">);</span> 1192 <span class="comment">//Check "MyClass" is still there</span> 1193 <span class="identifier">MyClass</span> <span class="special">*</span><span class="identifier">myclass</span> <span class="special">=</span> <span class="identifier">shm</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>(</span><span class="string">"MyClass"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span> 1194 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myclass</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 1195 <span class="comment">//The managed segment is unmapped here</span> 1196 <span class="special">}</span> 1197 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1198<span class="special">}</span> 1199</pre> 1200<p> 1201 </p> 1202<p> 1203 <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_mapped_file.html" title="Type definition managed_mapped_file">managed_mapped_file</a></code> 1204 also offers a similar function to grow or shrink_to_fit the managed file. 1205 Please, remember that <span class="bold"><strong>no process should be modifying 1206 the file/shared memory while the growing/shrinking process is performed</strong></span>. 1207 Otherwise, the managed segment will be corrupted. 1208 </p> 1209</div> 1210<div class="section"> 1211<div class="titlepage"><div><div><h4 class="title"> 1212<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_advanced_index_functions" title="Advanced index functions">Advanced 1213 index functions</a> 1214</h4></div></div></div> 1215<p> 1216 As mentioned, the managed segment stores the information about named and 1217 unique objects in two indexes. Depending on the type of those indexes, 1218 the index must reallocate some auxiliary structures when new named or unique 1219 allocations are made. For some indexes, if the user knows how many named 1220 or unique objects are going to be created it's possible to preallocate 1221 some structures to obtain much better performance. (If the index is an 1222 ordered vector it can preallocate memory to avoid reallocations. If the 1223 index is a hash structure it can preallocate the bucket array). 1224 </p> 1225<p> 1226 The following functions reserve memory to make the subsequent allocation 1227 of named or unique objects more efficient. These functions are only useful 1228 for pseudo-intrusive or non-node indexes (like <code class="computeroutput"><span class="identifier">flat_map_index</span></code>, 1229 <code class="computeroutput"><span class="identifier">iunordered_set_index</span></code>). 1230 These functions have no effect with the default index (<code class="computeroutput"><span class="identifier">iset_index</span></code>) 1231 or other indexes (<code class="computeroutput"><span class="identifier">map_index</span></code>): 1232 </p> 1233<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 1234<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_unique_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 1235</pre> 1236<pre class="programlisting"><span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 1237<span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">reserve_unique_objects</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 1238</pre> 1239<p> 1240 Managed memory segments also offer the possibility to iterate through constructed 1241 named and unique objects for debugging purposes. <span class="bold"><strong>Caution: 1242 this iteration is not thread-safe</strong></span> so the user should make sure 1243 that no other thread is manipulating named or unique indexes (creating, 1244 erasing, reserving...) in the segment. Other operations not involving indexes 1245 can be concurrently executed (raw memory allocation/deallocations, for 1246 example). 1247 </p> 1248<p> 1249 The following functions return constant iterators to the range of named 1250 and unique objects stored in the managed segment. Depending on the index 1251 type, iterators might be invalidated after a named or unique creation/erasure/reserve 1252 operation: 1253 </p> 1254<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">const_named_iterator</span> <span class="identifier">const_named_it</span><span class="special">;</span> 1255<span class="identifier">const_named_it</span> <span class="identifier">named_beg</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">named_begin</span><span class="special">();</span> 1256<span class="identifier">const_named_it</span> <span class="identifier">named_end</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">named_end</span><span class="special">();</span> 1257 1258<span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">const_unique_iterator</span> <span class="identifier">const_unique_it</span><span class="special">;</span> 1259<span class="identifier">const_unique_it</span> <span class="identifier">unique_beg</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">unique_begin</span><span class="special">();</span> 1260<span class="identifier">const_unique_it</span> <span class="identifier">unique_end</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">unique_end</span><span class="special">();</span> 1261 1262<span class="keyword">for</span><span class="special">(;</span> <span class="identifier">named_beg</span> <span class="special">!=</span> <span class="identifier">named_end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">named_beg</span><span class="special">){</span> 1263 <span class="comment">//A pointer to the name of the named object</span> 1264 <span class="keyword">const</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">char_type</span> <span class="special">*</span><span class="identifier">name</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-></span><span class="identifier">name</span><span class="special">();</span> 1265 <span class="comment">//The length of the name</span> 1266 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">name_len</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-></span><span class="identifier">name_length</span><span class="special">();</span> 1267 <span class="comment">//A constant void pointer to the named object</span> 1268 <span class="keyword">const</span> <span class="keyword">void</span> <span class="special">*</span><span class="identifier">value</span> <span class="special">=</span> <span class="identifier">named_beg</span><span class="special">-></span><span class="identifier">value</span><span class="special">();</span> 1269<span class="special">}</span> 1270 1271<span class="keyword">for</span><span class="special">(;</span> <span class="identifier">unique_beg</span> <span class="special">!=</span> <span class="identifier">unique_end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">unique_beg</span><span class="special">){</span> 1272 <span class="comment">//The typeid(T).name() of the unique object</span> 1273 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">typeid_name</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-></span><span class="identifier">name</span><span class="special">();</span> 1274 <span class="comment">//The length of the name</span> 1275 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">name_len</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-></span><span class="identifier">name_length</span><span class="special">();</span> 1276 <span class="comment">//A constant void pointer to the unique object</span> 1277 <span class="keyword">const</span> <span class="keyword">void</span> <span class="special">*</span><span class="identifier">value</span> <span class="special">=</span> <span class="identifier">unique_beg</span><span class="special">-></span><span class="identifier">value</span><span class="special">();</span> 1278<span class="special">}</span> 1279</pre> 1280</div> 1281<div class="section"> 1282<div class="titlepage"><div><div><h4 class="title"> 1283<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.allocate_aligned" title="Allocating aligned memory portions">Allocating 1284 aligned memory portions</a> 1285</h4></div></div></div> 1286<p> 1287 Sometimes it's interesting to be able to allocate aligned fragments of 1288 memory because of some hardware or software restrictions. Sometimes, having 1289 aligned memory is a feature that can be used to improve several memory 1290 algorithms. 1291 </p> 1292<p> 1293 This allocation is similar to the previously shown raw memory allocation 1294 but it takes an additional parameter specifying the alignment. There is 1295 a restriction for the alignment: <span class="bold"><strong>the alignment must 1296 be power of two</strong></span>. 1297 </p> 1298<p> 1299 If a user wants to allocate many aligned blocks (for example aligned to 1300 128 bytes), the size that minimizes the memory waste is a value that's 1301 is nearly a multiple of that alignment (for example 2*128 - some bytes). 1302 The reason for this is that every memory allocation usually needs some 1303 additional metadata in the first bytes of the allocated buffer. If the 1304 user can know the value of "some bytes" and if the first bytes 1305 of a free block of memory are used to fulfill the aligned allocation, the 1306 rest of the block can be left also aligned and ready for the next aligned 1307 allocation. Note that requesting <span class="bold"><strong>a size multiple 1308 of the alignment is not optimal</strong></span> because lefts the next block 1309 of memory unaligned due to the needed metadata. 1310 </p> 1311<p> 1312 Once the programmer knows the size of the payload of every memory allocation, 1313 he can request a size that will be optimal to allocate aligned chunks of 1314 memory maximizing both the size of the request <span class="bold"><strong>and</strong></span> 1315 the possibilities of future aligned allocations. This information is stored 1316 in the PayloadPerAllocation constant of managed memory segments. 1317 </p> 1318<p> 1319 Here is a small example showing how aligned allocation is used: 1320 </p> 1321<p> 1322</p> 1323<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1324<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 1325 1326<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 1327<span class="special">{</span> 1328 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 1329 1330 <span class="comment">//Remove shared memory on construction and destruction</span> 1331 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1332 <span class="special">{</span> 1333 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1334 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1335 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1336 1337 <span class="comment">//Managed memory segment that allocates portions of a shared memory</span> 1338 <span class="comment">//segment with the default management algorithm</span> 1339 <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 1340 1341 <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Alignment</span> <span class="special">=</span> <span class="number">128</span><span class="special">;</span> 1342 1343 <span class="comment">//Allocate 100 bytes aligned to Alignment from segment, throwing version</span> 1344 <span class="keyword">void</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">);</span> 1345 1346 <span class="comment">//Check alignment</span> 1347 <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 1348 1349 <span class="comment">//Deallocate it</span> 1350 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 1351 1352 <span class="comment">//Non throwing version</span> 1353 <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span><span class="special">(</span><span class="number">100</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">);</span> 1354 1355 <span class="comment">//Check alignment</span> 1356 <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 1357 1358 <span class="comment">//Deallocate it</span> 1359 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 1360 1361 <span class="comment">//If we want to efficiently allocate aligned blocks of memory</span> 1362 <span class="comment">//use managed_shared_memory::PayloadPerAllocation value</span> 1363 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">Alignment</span> <span class="special">></span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">PayloadPerAllocation</span><span class="special">);</span> 1364 1365 <span class="comment">//This allocation will maximize the size of the aligned memory</span> 1366 <span class="comment">//and will increase the possibility of finding more aligned memory</span> 1367 <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_aligned</span> 1368 <span class="special">(</span><span class="number">3</span><span class="special">*</span><span class="identifier">Alignment</span> <span class="special">-</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">PayloadPerAllocation</span><span class="special">,</span> <span class="identifier">Alignment</span><span class="special">);</span> 1369 1370 <span class="comment">//Check alignment</span> 1371 <span class="identifier">assert</span><span class="special">((</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="identifier">ptr</span><span class="special">)-</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="number">0</span><span class="special">))</span> <span class="special">%</span> <span class="identifier">Alignment</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 1372 1373 <span class="comment">//Deallocate it</span> 1374 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 1375 1376 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1377<span class="special">}</span> 1378</pre> 1379<p> 1380 </p> 1381</div> 1382<div class="section"> 1383<div class="titlepage"><div><div><h4 class="title"> 1384<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_multiple_allocations" title="Multiple allocation functions">Multiple 1385 allocation functions</a> 1386</h4></div></div></div> 1387<div class="caution"><table border="0" summary="Caution"> 1388<tr> 1389<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../doc/src/images/caution.png"></td> 1390<th align="left">Caution</th> 1391</tr> 1392<tr><td align="left" valign="top"><p> 1393 This feature is experimental, interface and ABI are unstable 1394 </p></td></tr> 1395</table></div> 1396<p> 1397 If an application needs to allocate a lot of memory buffers but it needs 1398 to deallocate them independently, the application is normally forced to 1399 loop calling <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>. 1400 Managed memory segments offer an alternative function to pack several allocations 1401 in a single call obtaining memory buffers that: 1402 </p> 1403<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1404<li class="listitem"> 1405 are packed contiguously in memory (which improves locality) 1406 </li> 1407<li class="listitem"> 1408 can be independently deallocated. 1409 </li> 1410</ul></div> 1411<p> 1412 This allocation method is much faster than calling <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code> in a loop. The downside is that the segment 1413 must provide a contiguous memory segment big enough to hold all the allocations. 1414 Managed memory segments offer this functionality through <code class="computeroutput"><span class="identifier">allocate_many</span><span class="special">()</span></code> 1415 functions. There are 2 types of <code class="computeroutput"><span class="identifier">allocate_many</span></code> 1416 functions: 1417 </p> 1418<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1419<li class="listitem"> 1420 Allocation of N buffers of memory with the same size. 1421 </li> 1422<li class="listitem"> 1423 Allocation of N buffers of memory, each one of different size. 1424 </li> 1425</ul></div> 1426<pre class="programlisting"><span class="comment">//!Allocates n_elements of elem_bytes bytes.</span> 1427<span class="comment">//!Throws bad_alloc on failure. chain.size() is not increased on failure.</span> 1428<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">size_type</span> <span class="identifier">elem_bytes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&</span><span class="identifier">chain</span><span class="special">);</span> 1429 1430<span class="comment">//!Allocates n_elements, each one of element_lengths[i]*sizeof_element bytes.</span> 1431<span class="comment">//!Throws bad_alloc on failure. chain.size() is not increased on failure.</span> 1432<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">size_type</span> <span class="special">*</span><span class="identifier">element_lengths</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">sizeof_element</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&</span><span class="identifier">chain</span><span class="special">);</span> 1433 1434<span class="comment">//!Allocates n_elements of elem_bytes bytes.</span> 1435<span class="comment">//!Non-throwing version. chain.size() is not increased on failure.</span> 1436<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow_t</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">elem_bytes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&</span><span class="identifier">chain</span><span class="special">);</span> 1437 1438<span class="comment">//!Allocates n_elements, each one of</span> 1439<span class="comment">//!element_lengths[i]*sizeof_element bytes.</span> 1440<span class="comment">//!Non-throwing version. chain.size() is not increased on failure.</span> 1441<span class="keyword">void</span> <span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow_t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">size_type</span> <span class="special">*</span><span class="identifier">elem_sizes</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">n_elements</span><span class="special">,</span> <span class="identifier">size_type</span> <span class="identifier">sizeof_element</span><span class="special">,</span> <span class="identifier">multiallocation_chain</span> <span class="special">&</span><span class="identifier">chain</span><span class="special">);</span> 1442 1443<span class="comment">//!Deallocates all elements contained in chain.</span> 1444<span class="comment">//!Never throws.</span> 1445<span class="keyword">void</span> <span class="identifier">deallocate_many</span><span class="special">(</span><span class="identifier">multiallocation_chain</span> <span class="special">&</span><span class="identifier">chain</span><span class="special">);</span> 1446</pre> 1447<p> 1448 Here is a small example showing all this functionality: 1449 </p> 1450<p> 1451</p> 1452<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1453<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">utility_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="comment">//boost::move</span> 1454<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">>//</span><span class="identifier">assert</span> 1455<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstring</span><span class="special">>//</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">memset</span> 1456<span class="preprocessor">#include</span> <span class="special"><</span><span class="keyword">new</span><span class="special">></span> <span class="comment">//std::nothrow</span> 1457<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> <span class="comment">//std::vector</span> 1458 1459<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 1460<span class="special">{</span> 1461 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 1462 <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">multiallocation_chain</span> <span class="identifier">multiallocation_chain</span><span class="special">;</span> 1463 1464 <span class="comment">//Remove shared memory on construction and destruction</span> 1465 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1466 <span class="special">{</span> 1467 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1468 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1469 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1470 1471 <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span><span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 1472 1473 <span class="comment">//Allocate 16 elements of 100 bytes in a single call. Non-throwing version.</span> 1474 <span class="identifier">multiallocation_chain</span> <span class="identifier">chain</span><span class="special">;</span> 1475 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">nothrow</span><span class="special">,</span> <span class="number">100</span><span class="special">,</span> <span class="number">16</span><span class="special">,</span> <span class="identifier">chain</span><span class="special">);</span> 1476 1477 <span class="comment">//Check if the memory allocation was successful</span> 1478 <span class="keyword">if</span><span class="special">(</span><span class="identifier">chain</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 1479 1480 <span class="comment">//Allocated buffers</span> 1481 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">void</span><span class="special">*></span> <span class="identifier">allocated_buffers</span><span class="special">;</span> 1482 1483 <span class="comment">//Initialize our data</span> 1484 <span class="keyword">while</span><span class="special">(!</span><span class="identifier">chain</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()){</span> 1485 <span class="keyword">void</span> <span class="special">*</span><span class="identifier">buf</span> <span class="special">=</span> <span class="identifier">chain</span><span class="special">.</span><span class="identifier">pop_front</span><span class="special">();</span> 1486 <span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">buf</span><span class="special">);</span> 1487 <span class="comment">//The iterator must be incremented before overwriting memory</span> 1488 <span class="comment">//because otherwise, the iterator is invalidated.</span> 1489 <span class="identifier">std</span><span class="special">::</span><span class="identifier">memset</span><span class="special">(</span><span class="identifier">buf</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="number">100</span><span class="special">);</span> 1490 <span class="special">}</span> 1491 1492 <span class="comment">//Now deallocate</span> 1493 <span class="keyword">while</span><span class="special">(!</span><span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()){</span> 1494 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">back</span><span class="special">());</span> 1495 <span class="identifier">allocated_buffers</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> 1496 <span class="special">}</span> 1497 1498 <span class="comment">//Allocate 10 buffers of different sizes in a single call. Throwing version</span> 1499 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">sizes</span><span class="special">[</span><span class="number">10</span><span class="special">];</span> 1500 <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">10</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> 1501 <span class="identifier">sizes</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">*</span><span class="number">3</span><span class="special">;</span> 1502 1503 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocate_many</span><span class="special">(</span><span class="identifier">sizes</span><span class="special">,</span> <span class="number">10</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">chain</span><span class="special">);</span> 1504 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate_many</span><span class="special">(</span><span class="identifier">chain</span><span class="special">);</span> 1505 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1506<span class="special">}</span> 1507</pre> 1508<p> 1509 </p> 1510<p> 1511 Allocating N buffers of the same size improves the performance of pools 1512 and node containers (for example STL-like lists): when inserting a range 1513 of forward iterators in a STL-like list, the insertion function can detect 1514 the number of needed elements and allocate in a single call. The nodes 1515 still can be deallocated. 1516 </p> 1517<p> 1518 Allocating N buffers of different sizes can be used to speed up allocation 1519 in cases where several objects must always be allocated at the same time 1520 but deallocated at different times. For example, a class might perform 1521 several initial allocations (some header data for a network packet, for 1522 example) in its constructor but also allocations of buffers that might 1523 be reallocated in the future (the data to be sent through the network). 1524 Instead of allocating all the data independently, the constructor might 1525 use <code class="computeroutput"><span class="identifier">allocate_many</span><span class="special">()</span></code> 1526 to speed up the initialization, but it still can deallocate and expand 1527 the memory of the variable size element. 1528 </p> 1529<p> 1530 In general, <code class="computeroutput"><span class="identifier">allocate_many</span></code> 1531 is useful with large values of N. Overuse of <code class="computeroutput"><span class="identifier">allocate_many</span></code> 1532 can increase the effective memory usage, because it can't reuse existing 1533 non-contiguous memory fragments that might be available for some of the 1534 elements. 1535 </p> 1536</div> 1537<div class="section"> 1538<div class="titlepage"><div><div><h4 class="title"> 1539<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.managed_memory_segment_expand_in_place" title="Expand in place memory allocation">Expand 1540 in place memory allocation</a> 1541</h4></div></div></div> 1542<p> 1543 When programming some data structures such as vectors, memory reallocation 1544 becomes an important tool to improve performance. Managed memory segments 1545 offer an advanced reallocation function that offers: 1546 </p> 1547<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1548<li class="listitem"> 1549 Forward expansion: An allocated buffer can be expanded so that the 1550 end of the buffer is moved further. New data can be written between 1551 the old end and the new end. 1552 </li> 1553<li class="listitem"> 1554 Backwards expansion: An allocated buffer can be expanded so that the 1555 beginning of the buffer is moved backwards. New data can be written 1556 between the new beginning and the old beginning. 1557 </li> 1558<li class="listitem"> 1559 Shrinking: An allocated buffer can be shrunk so that the end of the 1560 buffer is moved backwards. The memory between the new end and the old 1561 end can be reused for future allocations. 1562 </li> 1563</ul></div> 1564<p> 1565 The expansion can be combined with the allocation of a new buffer if the 1566 expansion fails obtaining a function with "expand, if fails allocate 1567 a new buffer" semantics. 1568 </p> 1569<p> 1570 Apart from this features, the function always returns the real size of 1571 the allocated buffer, because many times, due to alignment issues the allocated 1572 buffer a bit bigger than the requested size. Thus, the programmer can maximize 1573 the memory use using <code class="computeroutput"><span class="identifier">allocation_command</span></code>. 1574 </p> 1575<p> 1576 Here is the declaration of the function: 1577 </p> 1578<pre class="programlisting"><span class="keyword">enum</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocation_type</span> 1579<span class="special">{</span> 1580 <span class="comment">//Bitwise OR (|) combinable values</span> 1581 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span> <span class="special">=</span> <span class="special">...,</span> 1582 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span> <span class="special">=</span> <span class="special">...,</span> 1583 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span> <span class="special">=</span> <span class="special">...,</span> 1584 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span> <span class="special">=</span> <span class="special">...,</span> 1585 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span> <span class="special">=</span> <span class="special">...</span> 1586<span class="special">};</span> 1587 1588 1589<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 1590<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">T</span> <span class="special">*,</span> <span class="keyword">bool</span><span class="special">></span> 1591 <span class="identifier">allocation_command</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocation_type</span> <span class="identifier">command</span> 1592 <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">limit_size</span> 1593 <span class="special">,</span> <span class="identifier">size_type</span> <span class="special">&</span><span class="identifier">prefer_in_recvd_out_size</span> 1594 <span class="special">,</span> <span class="identifier">T</span> <span class="special">*&</span><span class="identifier">reuse_ptr</span><span class="special">);</span> 1595</pre> 1596<p> 1597 <span class="bold"><strong>Preconditions for the function</strong></span>: 1598 </p> 1599<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1600<li class="listitem"> 1601 If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code> 1602 it can't contain any of these values: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code>, 1603 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>. 1604 </li> 1605<li class="listitem"> 1606 If the parameter command contains <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1607 or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, the parameter <code class="computeroutput"><span class="identifier">reuse_ptr</span></code> must be non-null and returned 1608 by a previous allocation function. 1609 </li> 1610<li class="listitem"> 1611 If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code>, 1612 the parameter <code class="computeroutput"><span class="identifier">limit_size</span></code> 1613 must be equal or greater than the parameter <code class="computeroutput"><span class="identifier">preferred_size</span></code>. 1614 </li> 1615<li class="listitem"> 1616 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1617 contains any of these values: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1618 or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, the parameter <code class="computeroutput"><span class="identifier">limit_size</span></code> must be equal or less 1619 than the parameter <code class="computeroutput"><span class="identifier">preferred_size</span></code>. 1620 </li> 1621</ul></div> 1622<p> 1623 <span class="bold"><strong>Which are the effects of this function:</strong></span> 1624 </p> 1625<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1626<li class="listitem"> 1627 If the parameter command contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span></code>, 1628 the function will try to reduce the size of the memory block referenced 1629 by pointer <code class="computeroutput"><span class="identifier">reuse_ptr</span></code> 1630 to the value <code class="computeroutput"><span class="identifier">preferred_size</span></code> 1631 moving only the end of the block. If it's not possible, it will try 1632 to reduce the size of the memory block as much as possible as long 1633 as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special"><=</span> <span class="identifier">limit_size</span></code>. Success is reported only 1634 if this results in <code class="computeroutput"><span class="identifier">preferred_size</span> 1635 <span class="special"><=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code> and <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special"><=</span> <span class="identifier">limit_size</span></code>. 1636 </li> 1637<li class="listitem"> 1638 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1639 only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1640 (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), 1641 the allocator will try to increase the size of the memory block referenced 1642 by pointer reuse moving only the end of the block to the value <code class="computeroutput"><span class="identifier">preferred_size</span></code>. If it's not possible, 1643 it will try to increase the size of the memory block as much as possible 1644 as long as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">>=</span> <span class="identifier">limit_size</span></code>. Success is reported only 1645 if this results in <code class="computeroutput"><span class="identifier">limit_size</span> 1646 <span class="special"><=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code>. 1647 </li> 1648<li class="listitem"> 1649 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1650 only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code> 1651 (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), 1652 the allocator will try to increase the size of the memory block referenced 1653 by pointer <code class="computeroutput"><span class="identifier">reuse_ptr</span></code> 1654 only moving the start of the block to a returned new position <code class="computeroutput"><span class="identifier">new_ptr</span></code>. If it's not possible, it 1655 will try to move the start of the block as much as possible as long 1656 as this results in <code class="computeroutput"><span class="identifier">size</span><span class="special">(</span><span class="identifier">new_ptr</span><span class="special">)</span> <span class="special">>=</span> <span class="identifier">limit_size</span></code>. Success is reported only 1657 if this results in <code class="computeroutput"><span class="identifier">limit_size</span> 1658 <span class="special"><=</span> <span class="identifier">size</span><span class="special">(</span><span class="identifier">new_ptr</span><span class="special">)</span></code>. 1659 </li> 1660<li class="listitem"> 1661 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1662 only contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code> 1663 (with optional additional <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), 1664 the allocator will try to allocate memory for <code class="computeroutput"><span class="identifier">preferred_size</span></code> 1665 objects. If it's not possible it will try to allocate memory for at 1666 least <code class="computeroutput"><span class="identifier">limit_size</span></code> objects. 1667 </li> 1668<li class="listitem"> 1669 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1670 only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1671 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code>, (with optional additional 1672 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>) the allocator 1673 will try first the forward expansion. If this fails, it would try a 1674 new allocation. 1675 </li> 1676<li class="listitem"> 1677 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1678 only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code> 1679 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span></code> (with optional additional 1680 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), the allocator 1681 will try first to obtain <code class="computeroutput"><span class="identifier">preferred_size</span></code> 1682 objects using both methods if necessary. If this fails, it will try 1683 to obtain <code class="computeroutput"><span class="identifier">limit_size</span></code> 1684 objects using both methods if necessary. 1685 </li> 1686<li class="listitem"> 1687 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1688 only contains a combination of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1689 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code> (with optional additional 1690 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>), the allocator 1691 will try first forward expansion. If this fails it will try to obtain 1692 preferred_size objects using backwards expansion or a combination of 1693 forward and backwards expansion. If this fails, it will try to obtain 1694 <code class="computeroutput"><span class="identifier">limit_size</span></code> objects 1695 using both methods if necessary. 1696 </li> 1697<li class="listitem"> 1698 If the parameter <code class="computeroutput"><span class="identifier">command</span></code> 1699 only contains a combination of allocation_new, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span></code> 1700 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_bwd</span></code>, (with optional additional 1701 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>) the allocator 1702 will try first forward expansion. If this fails it will try to obtain 1703 preferred_size objects using new allocation, backwards expansion or 1704 a combination of forward and backwards expansion. If this fails, it 1705 will try to obtain <code class="computeroutput"><span class="identifier">limit_size</span></code> 1706 objects using the same methods. 1707 </li> 1708<li class="listitem"> 1709 The allocator always writes the size or the expanded/allocated/shrunk 1710 memory block in <code class="computeroutput"><span class="identifier">received_size</span></code>. 1711 On failure the allocator writes in <code class="computeroutput"><span class="identifier">received_size</span></code> 1712 a possibly successful <code class="computeroutput"><span class="identifier">limit_size</span></code> 1713 parameter for a new call. 1714 </li> 1715</ul></div> 1716<p> 1717 <span class="bold"><strong>Throws an exception if two conditions are met:</strong></span> 1718 </p> 1719<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1720<li class="listitem"> 1721 The allocator is unable to allocate/expand/shrink the memory or there 1722 is an error in preconditions 1723 </li> 1724<li class="listitem"> 1725 The parameter command does not contain <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code>. 1726 </li> 1727</ul></div> 1728<p> 1729 <span class="bold"><strong>This function returns:</strong></span> 1730 </p> 1731<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1732<li class="listitem"> 1733 The address of the allocated memory or the new address of the expanded 1734 memory as the first member of the pair. If the parameter command contains 1735 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">nothrow_allocation</span></code> the first member 1736 will be 0 if the allocation/expansion fails or there is an error in 1737 preconditions. 1738 </li> 1739<li class="listitem"> 1740 The second member of the pair will be false if the memory has been 1741 allocated, true if the memory has been expanded. If the first member 1742 is 0, the second member has an undefined value. 1743 </li> 1744</ul></div> 1745<p> 1746 <span class="bold"><strong>Notes:</strong></span> 1747 </p> 1748<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1749<li class="listitem"> 1750 If the user chooses <code class="computeroutput"><span class="keyword">char</span></code> 1751 as template argument the returned buffer will be suitably aligned to 1752 hold any type. 1753 </li> 1754<li class="listitem"> 1755 If the user chooses <code class="computeroutput"><span class="keyword">char</span></code> 1756 as template argument and a backwards expansion is performed, although 1757 properly aligned, the returned buffer might not be suitable because 1758 the distance between the new beginning and the old beginning might 1759 not multiple of the type the user wants to construct, since due to 1760 internal restrictions the expansion can be slightly bigger than the 1761 requested bytes. <span class="bold"><strong>When performing backwards expansion, 1762 if you have already constructed objects in the old buffer, make sure 1763 to specify correctly the type.</strong></span> 1764 </li> 1765</ul></div> 1766<p> 1767 Here is a small example that shows the use of <code class="computeroutput"><span class="identifier">allocation_command</span></code>: 1768 </p> 1769<p> 1770</p> 1771<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1772<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 1773 1774<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 1775<span class="special">{</span> 1776 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 1777 1778 <span class="comment">//Remove shared memory on construction and destruction</span> 1779 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1780 <span class="special">{</span> 1781 <span class="identifier">shm_remove</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1782 <span class="special">~</span><span class="identifier">shm_remove</span><span class="special">(){</span> <span class="identifier">shared_memory_object</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="string">"MySharedMemory"</span><span class="special">);</span> <span class="special">}</span> 1783 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1784 1785 <span class="comment">//Managed memory segment that allocates portions of a shared memory</span> 1786 <span class="comment">//segment with the default management algorithm</span> 1787 <span class="identifier">managed_shared_memory</span> <span class="identifier">managed_shm</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="number">10000</span><span class="special">*</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">));</span> 1788 1789 <span class="comment">//Allocate at least 100 bytes, 1000 bytes if possible</span> 1790 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">min_size</span> <span class="special">=</span> <span class="number">100</span><span class="special">;</span> 1791 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">first_received_size</span> <span class="special">=</span> <span class="number">1000</span><span class="special">;</span> 1792 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">*</span><span class="identifier">hint</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 1793 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">*</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> 1794 <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">allocate_new</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">,</span> <span class="identifier">first_received_size</span><span class="special">,</span> <span class="identifier">hint</span><span class="special">);</span> 1795 1796 <span class="comment">//Received size must be bigger than min_size</span> 1797 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">first_received_size</span> <span class="special">>=</span> <span class="identifier">min_size</span><span class="special">);</span> 1798 1799 <span class="comment">//Get free memory</span> 1800 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_allocation</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span> 1801 1802 <span class="comment">//Now write the data</span> 1803 <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">first_received_size</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">ptr</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> 1804 1805 <span class="comment">//Now try to triplicate the buffer. We won't admit an expansion</span> 1806 <span class="comment">//lower to the double of the original buffer.</span> 1807 <span class="comment">//This "should" be successful since no other class is allocating</span> 1808 <span class="comment">//memory from the segment</span> 1809 <span class="identifier">min_size</span> <span class="special">=</span> <span class="identifier">first_received_size</span><span class="special">*</span><span class="number">2</span><span class="special">;</span> 1810 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">expanded_size</span> <span class="special">=</span> <span class="identifier">first_received_size</span><span class="special">*</span><span class="number">3</span><span class="special">;</span> 1811 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="special">*</span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span> 1812 <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">expand_fwd</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">,</span> <span class="identifier">expanded_size</span><span class="special">,</span> <span class="identifier">ptr</span><span class="special">);</span> 1813 <span class="comment">//Check invariants</span> 1814 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ptr</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 1815 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span> <span class="special">==</span> <span class="identifier">ptr</span><span class="special">);</span> 1816 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">expanded_size</span> <span class="special">>=</span> <span class="identifier">first_received_size</span><span class="special">*</span><span class="number">2</span><span class="special">);</span> 1817 1818 <span class="comment">//Get free memory and compare</span> 1819 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_expansion</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span> 1820 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">free_memory_after_expansion</span> <span class="special"><</span> <span class="identifier">free_memory_after_allocation</span><span class="special">);</span> 1821 1822 <span class="comment">//Write new values</span> 1823 <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">first_received_size</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">expanded_size</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">ptr</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> 1824 1825 <span class="comment">//Try to shrink approximately to min_size, but the new size</span> 1826 <span class="comment">//should be smaller than min_size*2.</span> 1827 <span class="comment">//This "should" be successful since no other class is allocating</span> 1828 <span class="comment">//memory from the segment</span> 1829 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">shrunk_size</span> <span class="special">=</span> <span class="identifier">min_size</span><span class="special">;</span> 1830 <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">allocation_command</span> 1831 <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">shrink_in_place</span><span class="special">,</span> <span class="identifier">min_size</span><span class="special">*</span><span class="number">2</span><span class="special">,</span> <span class="identifier">shrunk_size</span><span class="special">,</span> <span class="identifier">ptr</span><span class="special">);</span> 1832 1833 <span class="comment">//Check invariants</span> 1834 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ptr</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 1835 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">ret</span> <span class="special">==</span> <span class="identifier">ptr</span><span class="special">);</span> 1836 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shrunk_size</span> <span class="special"><=</span> <span class="identifier">min_size</span><span class="special">*</span><span class="number">2</span><span class="special">);</span> 1837 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shrunk_size</span> <span class="special">>=</span> <span class="identifier">min_size</span><span class="special">);</span> 1838 1839 <span class="comment">//Get free memory and compare</span> 1840 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">free_memory_after_shrinking</span> <span class="special">=</span> <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">get_free_memory</span><span class="special">();</span> 1841 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">free_memory_after_shrinking</span> <span class="special">></span> <span class="identifier">free_memory_after_expansion</span><span class="special">);</span> 1842 1843 <span class="comment">//Deallocate the buffer</span> 1844 <span class="identifier">managed_shm</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">);</span> 1845 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1846<span class="special">}</span> 1847</pre> 1848<p> 1849 </p> 1850<p> 1851 <code class="computeroutput"><span class="identifier">allocation_command</span></code> is a 1852 very powerful function that can lead to important performance gains. It's 1853 specially useful when programming vector-like data structures where the 1854 programmer can minimize both the number of allocation requests and the 1855 memory waste. 1856 </p> 1857</div> 1858<div class="section"> 1859<div class="titlepage"><div><div><h4 class="title"> 1860<a name="interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_advanced_features.copy_on_write_read_only" title="Opening managed shared memory and mapped files with Copy On Write or Read Only modes">Opening 1861 managed shared memory and mapped files with Copy On Write or Read Only modes</a> 1862</h4></div></div></div> 1863<p> 1864 When mapping a memory segment based on shared memory or files, there is 1865 an option to open them using <span class="bold"><strong>open_copy_on_write</strong></span> 1866 option. This option is similar to <code class="computeroutput"><span class="identifier">open_only</span></code> 1867 but every change the programmer does with this managed segment is kept 1868 private to this process and is not translated to the underlying device 1869 (shared memory or file). 1870 </p> 1871<p> 1872 The underlying shared memory or file is opened as read-only so several 1873 processes can share an initial managed segment and make private changes 1874 to it. If many processes open a managed segment in copy on write mode and 1875 not modified pages from the managed segment will be shared between all 1876 those processes, with considerable memory savings. 1877 </p> 1878<p> 1879 Opening managed shared memory and mapped files with <span class="bold"><strong>open_read_only</strong></span> 1880 maps the underlying device in memory with <span class="bold"><strong>read-only</strong></span> 1881 attributes. This means that any attempt to write that memory, either creating 1882 objects or locking any mutex might result in an page-fault error (and thus, 1883 program termination) from the OS. Read-only mode opens the underlying device 1884 (shared memory, file...) in read-only mode and can result in considerable 1885 memory savings if several processes just want to process a managed memory 1886 segment without modifying it. Read-only mode operations are limited: 1887 </p> 1888<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1889<li class="listitem"> 1890 Read-only mode must be used only from managed classes. If the programmer 1891 obtains the segment manager and tries to use it directly it might result 1892 in an access violation. The reason for this is that the segment manager 1893 is placed in the underlying device and does not nothing about the mode 1894 it's been mapped in memory. 1895 </li> 1896<li class="listitem"> 1897 Only const member functions from managed segments should be used. 1898 </li> 1899<li class="listitem"> 1900 Additionally, the <code class="computeroutput"><span class="identifier">find</span><span class="special"><></span></code> member function avoids using 1901 internal locks and can be used to look for named and unique objects. 1902 </li> 1903</ul></div> 1904<p> 1905 Here is an example that shows the use of these two open modes: 1906 </p> 1907<p> 1908</p> 1909<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1910<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">fstream</span><span class="special">></span> <span class="comment">//std::fstream</span> 1911<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iterator</span><span class="special">>//</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span> 1912 1913 1914<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 1915<span class="special">{</span> 1916 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 1917 1918 <span class="comment">//Define file names</span> 1919 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">ManagedFile</span> <span class="special">=</span> <span class="string">"MyManagedFile"</span><span class="special">;</span> 1920 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">ManagedFile2</span> <span class="special">=</span> <span class="string">"MyManagedFile2"</span><span class="special">;</span> 1921 1922 <span class="comment">//Try to erase any previous managed segment with the same name</span> 1923 <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">ManagedFile</span><span class="special">);</span> 1924 <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">);</span> 1925 <span class="identifier">remove_file_on_destroy</span> <span class="identifier">destroyer1</span><span class="special">(</span><span class="identifier">ManagedFile</span><span class="special">);</span> 1926 <span class="identifier">remove_file_on_destroy</span> <span class="identifier">destroyer2</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">);</span> 1927 1928 <span class="special">{</span> 1929 <span class="comment">//Create an named integer in a managed mapped file</span> 1930 <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 1931 <span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">)(</span><span class="number">0u</span><span class="special">);</span> 1932 1933 <span class="comment">//Now create a copy on write version</span> 1934 <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_cow</span><span class="special">(</span><span class="identifier">open_copy_on_write</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">);</span> 1935 1936 <span class="comment">//Erase the int and create a new one</span> 1937 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">))</span> 1938 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1939 <span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt2"</span><span class="special">);</span> 1940 1941 <span class="comment">//Check changes</span> 1942 <span class="keyword">if</span><span class="special">(</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&&</span> <span class="special">!</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 1943 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1944 1945 <span class="comment">//Check the original is intact</span> 1946 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&&</span> <span class="identifier">managed_file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 1947 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1948 1949 <span class="special">{</span> <span class="comment">//Dump the modified copy on write segment to a file</span> 1950 <span class="identifier">std</span><span class="special">::</span><span class="identifier">fstream</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">ManagedFile2</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">out</span> <span class="special">|</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">binary</span><span class="special">);</span> 1951 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">file</span><span class="special">)</span> 1952 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1953 <span class="identifier">file</span><span class="special">.</span><span class="identifier">write</span><span class="special">(</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*>(</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">get_address</span><span class="special">()),</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">streamsize</span><span class="special">)</span><span class="identifier">managed_file_cow</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">());</span> 1954 <span class="special">}</span> 1955 1956 <span class="comment">//Now open the modified file and test changes</span> 1957 <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_cow2</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">ManagedFile2</span><span class="special">);</span> 1958 <span class="keyword">if</span><span class="special">(</span><span class="identifier">managed_file_cow2</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&&</span> <span class="special">!</span><span class="identifier">managed_file_cow2</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 1959 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1960 <span class="special">}</span> 1961 <span class="special">{</span> 1962 <span class="comment">//Now create a read-only version</span> 1963 <span class="identifier">managed_mapped_file</span> <span class="identifier">managed_file_ro</span><span class="special">(</span><span class="identifier">open_read_only</span><span class="special">,</span> <span class="identifier">ManagedFile</span><span class="special">);</span> 1964 1965 <span class="comment">//Check the original is intact</span> 1966 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">&&</span> <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"MyInt2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 1967 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1968 1969 <span class="comment">//Check the number of named objects using the iterators</span> 1970 <span class="keyword">if</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">named_begin</span><span class="special">(),</span> <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">named_end</span><span class="special">())</span> <span class="special">!=</span> <span class="number">1</span> <span class="special">&&</span> 1971 <span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span><span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">unique_begin</span><span class="special">(),</span> <span class="identifier">managed_file_ro</span><span class="special">.</span><span class="identifier">unique_end</span><span class="special">())</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">)</span> 1972 <span class="keyword">throw</span> <span class="keyword">int</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> 1973 <span class="special">}</span> 1974 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1975<span class="special">}</span> 1976</pre> 1977<p> 1978 </p> 1979</div> 1980</div> 1981<div class="section"> 1982<div class="titlepage"><div><div><h3 class="title"> 1983<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer" title="Managed Heap Memory And Managed External Buffer">Managed 1984 Heap Memory And Managed External Buffer</a> 1985</h3></div></div></div> 1986<div class="toc"><dl class="toc"> 1987<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer">Managed 1988 External Buffer: Constructing all Boost.Interprocess objects in a user provided 1989 buffer</a></span></dt> 1990<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory">Managed 1991 Heap Memory: Boost.Interprocess machinery in heap memory</a></span></dt> 1992<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff">Differences 1993 between managed memory segments</a></span></dt> 1994<dt><span class="section"><a href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex">Example: 1995 Serializing a database through the message queue</a></span></dt> 1996</dl></div> 1997<p> 1998 <span class="bold"><strong>Boost.Interprocess</strong></span> offers managed shared 1999 memory between processes using <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> 2000 or <code class="computeroutput"><span class="identifier">managed_mapped_file</span></code>. Two 2001 processes just map the same the memory mappable resource and read from and 2002 write to that object. 2003 </p> 2004<p> 2005 Many times, we don't want to use that shared memory approach and we prefer 2006 to send serialized data through network, local socket or message queues. 2007 Serialization can be done through <span class="bold"><strong>Boost.Serialization</strong></span> 2008 or similar library. However, if two processes share the same ABI (application 2009 binary interface), we could use the same object and container construction 2010 capabilities of <code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> 2011 or <code class="computeroutput"><span class="identifier">managed_heap_memory</span></code> to 2012 build all the information in a single buffer that will be sent, for example, 2013 though message queues. The receiver would just copy the data to a local buffer, 2014 and it could read or modify it directly without deserializing the data . 2015 This approach can be much more efficient that a complex serialization mechanism. 2016 </p> 2017<p> 2018 Applications for <span class="bold"><strong>Boost.Interprocess</strong></span> services 2019 using non-shared memory buffers: 2020 </p> 2021<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 2022<li class="listitem"> 2023 Create and use STL compatible containers and allocators, in systems where 2024 dynamic memory is not recommendable. 2025 </li> 2026<li class="listitem"> 2027 Build complex, easily serializable databases in a single buffer: 2028 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 2029<li class="listitem"> 2030 To share data between threads 2031 </li> 2032<li class="listitem"> 2033 To save and load information from/to files. 2034 </li> 2035</ul></div> 2036 </li> 2037<li class="listitem"> 2038 Duplicate information (containers, allocators, etc...) just copying the 2039 contents of one buffer to another one. 2040 </li> 2041<li class="listitem"> 2042 Send complex information and objects/databases using serial/inter-process/network 2043 communications. 2044 </li> 2045</ul></div> 2046<p> 2047 To help with this management, <span class="bold"><strong>Boost.Interprocess</strong></span> 2048 provides two useful classes, <code class="computeroutput"><span class="identifier">basic_managed_heap_memory</span></code> 2049 and <code class="computeroutput"><span class="identifier">basic_managed_external_buffer</span></code>: 2050 </p> 2051<div class="section"> 2052<div class="titlepage"><div><div><h4 class="title"> 2053<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_external_buffer" title="Managed External Buffer: Constructing all Boost.Interprocess objects in a user provided buffer">Managed 2054 External Buffer: Constructing all Boost.Interprocess objects in a user provided 2055 buffer</a> 2056</h4></div></div></div> 2057<p> 2058 Sometimes, the user wants to create simple objects, STL compatible containers, 2059 STL compatible strings and more, all in a single buffer. This buffer could 2060 be a big static buffer, a memory-mapped auxiliary device or any other user 2061 buffer. 2062 </p> 2063<p> 2064 This would allow an easy serialization and we-ll just need to copy the 2065 buffer to duplicate all the objects created in the original buffer, including 2066 complex objects like maps, lists.... <span class="bold"><strong>Boost.Interprocess</strong></span> 2067 offers managed memory segment classes to handle user provided buffers that 2068 allow the same functionality as shared memory classes: 2069 </p> 2070<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span> 2071<span class="comment">//All objects are constructed in a user provided buffer</span> 2072<span class="keyword">template</span> <span class="special"><</span> 2073 <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> 2074 <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span> 2075 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">IndexType</span> 2076 <span class="special">></span> 2077<span class="keyword">class</span> <span class="identifier">basic_managed_external_buffer</span><span class="special">;</span> 2078 2079<span class="comment">//Named object creation managed memory segment</span> 2080<span class="comment">//All objects are constructed in a user provided buffer</span> 2081<span class="comment">// Names are c-strings,</span> 2082<span class="comment">// Default memory management algorithm</span> 2083<span class="comment">// (rbtree_best_fit with no mutexes and relative pointers)</span> 2084<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 2085<span class="keyword">typedef</span> <span class="identifier">basic_managed_external_buffer</span> <span class="special"><</span> 2086 <span class="keyword">char</span><span class="special">,</span> 2087 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">null_mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">>,</span> 2088 <span class="identifier">flat_map_index</span> 2089 <span class="special">></span> <span class="identifier">managed_external_buffer</span><span class="special">;</span> 2090 2091<span class="comment">//Named object creation managed memory segment</span> 2092<span class="comment">//All objects are constructed in a user provided buffer</span> 2093<span class="comment">// Names are wide-strings,</span> 2094<span class="comment">// Default memory management algorithm</span> 2095<span class="comment">// (rbtree_best_fit with no mutexes and relative pointers)</span> 2096<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 2097<span class="keyword">typedef</span> <span class="identifier">basic_managed_external_buffer</span><span class="special"><</span> 2098 <span class="keyword">wchar_t</span><span class="special">,</span> 2099 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">null_mutex_family</span><span class="special">,</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">>,</span> 2100 <span class="identifier">flat_map_index</span> 2101 <span class="special">></span> <span class="identifier">wmanaged_external_buffer</span><span class="special">;</span> 2102</pre> 2103<p> 2104 To use a managed external buffer, you must include the following header: 2105 </p> 2106<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_external_buffer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2107</pre> 2108<p> 2109 Let's see an example of the use of managed_external_buffer: 2110 </p> 2111<p> 2112</p> 2113<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_external_buffer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2114<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2115<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2116<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstring</span><span class="special">></span> 2117<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">aligned_storage</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2118 2119<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 2120<span class="special">{</span> 2121 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 2122 2123 <span class="comment">//Create the static memory who will store all objects</span> 2124 <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">memsize</span> <span class="special">=</span> <span class="number">65536</span><span class="special">;</span> 2125 2126 <span class="keyword">static</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">aligned_storage</span><span class="special"><</span><span class="identifier">memsize</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">static_buffer</span><span class="special">;</span> 2127 2128 <span class="comment">//This managed memory will construct objects associated with</span> 2129 <span class="comment">//a wide string in the static buffer</span> 2130 <span class="identifier">wmanaged_external_buffer</span> <span class="identifier">objects_in_static_memory</span> 2131 <span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="special">&</span><span class="identifier">static_buffer</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span> 2132 2133 <span class="comment">//We optimize resources to create 100 named objects in the static buffer</span> 2134 <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">reserve_named_objects</span><span class="special">(</span><span class="number">100</span><span class="special">);</span> 2135 2136 <span class="comment">//Alias an integer node allocator type</span> 2137 <span class="comment">//This allocator will allocate memory inside the static buffer</span> 2138 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">wmanaged_external_buffer</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 2139 <span class="identifier">allocator_t</span><span class="special">;</span> 2140 2141 <span class="comment">//Alias a STL compatible list to be constructed in the static buffer</span> 2142 <span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">allocator_t</span><span class="special">></span> <span class="identifier">MyBufferList</span><span class="special">;</span> 2143 2144 <span class="comment">//The list must be initialized with the allocator</span> 2145 <span class="comment">//All objects created with objects_in_static_memory will</span> 2146 <span class="comment">//be stored in the static_buffer!</span> 2147 <span class="identifier">MyBufferList</span> <span class="special">*</span><span class="identifier">list</span> <span class="special">=</span> <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyBufferList</span><span class="special">>(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">)</span> 2148 <span class="special">(</span><span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 2149 <span class="comment">//Since the allocation algorithm from wmanaged_external_buffer uses relative</span> 2150 <span class="comment">//pointers and all the pointers constructed int the static memory point</span> 2151 <span class="comment">//to objects in the same segment, we can create another static buffer</span> 2152 <span class="comment">//from the first one and duplicate all the data.</span> 2153 <span class="keyword">static</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">aligned_storage</span><span class="special"><</span><span class="identifier">memsize</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">static_buffer2</span><span class="special">;</span> 2154 <span class="identifier">std</span><span class="special">::</span><span class="identifier">memcpy</span><span class="special">(&</span><span class="identifier">static_buffer2</span><span class="special">,</span> <span class="special">&</span><span class="identifier">static_buffer</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span> 2155 2156 <span class="comment">//Now open the duplicated managed memory passing the memory as argument</span> 2157 <span class="identifier">wmanaged_external_buffer</span> <span class="identifier">objects_in_static_memory2</span> 2158 <span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="special">&</span><span class="identifier">static_buffer2</span><span class="special">,</span> <span class="identifier">memsize</span><span class="special">);</span> 2159 2160 <span class="comment">//Check that "MyList" has been duplicated in the second buffer</span> 2161 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">objects_in_static_memory2</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyBufferList</span><span class="special">>(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 2162 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 2163 2164 <span class="comment">//Destroy the lists from the static buffers</span> 2165 <span class="identifier">objects_in_static_memory</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">MyBufferList</span><span class="special">>(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">);</span> 2166 <span class="identifier">objects_in_static_memory2</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">MyBufferList</span><span class="special">>(</span><span class="identifier">L</span><span class="string">"MyList"</span><span class="special">);</span> 2167 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 2168<span class="special">}</span> 2169</pre> 2170<p> 2171 </p> 2172<p> 2173 <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators 2174 can also be used to place STL compatible containers in the user segment. 2175 </p> 2176<p> 2177 <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011784704.html" title="Class template basic_managed_external_buffer">basic_managed_external_buffer</a></code> 2178 can be also useful to build small databases for embedded systems limiting 2179 the size of the used memory to a predefined memory chunk, instead of letting 2180 the database fragment the heap memory. 2181 </p> 2182</div> 2183<div class="section"> 2184<div class="titlepage"><div><div><h4 class="title"> 2185<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory" title="Managed Heap Memory: Boost.Interprocess machinery in heap memory">Managed 2186 Heap Memory: Boost.Interprocess machinery in heap memory</a> 2187</h4></div></div></div> 2188<p> 2189 The use of heap memory (new/delete) to obtain a buffer where the user wants 2190 to store all his data is very common, so <span class="bold"><strong>Boost.Interprocess</strong></span> 2191 provides some specialized classes that work exclusively with heap memory. 2192 </p> 2193<p> 2194 These are the classes: 2195 </p> 2196<pre class="programlisting"><span class="comment">//Named object creation managed memory segment</span> 2197<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span> 2198<span class="keyword">template</span> <span class="special"><</span> 2199 <span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> 2200 <span class="keyword">class</span> <span class="identifier">MemoryAlgorithm</span><span class="special">,</span> 2201 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">IndexConfig</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">IndexType</span> 2202 <span class="special">></span> 2203<span class="keyword">class</span> <span class="identifier">basic_managed_heap_memory</span><span class="special">;</span> 2204 2205<span class="comment">//Named object creation managed memory segment</span> 2206<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span> 2207<span class="comment">// Names are c-strings,</span> 2208<span class="comment">// Default memory management algorithm</span> 2209<span class="comment">// (rbtree_best_fit with no mutexes and relative pointers)</span> 2210<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 2211<span class="keyword">typedef</span> <span class="identifier">basic_managed_heap_memory</span> <span class="special"><</span> 2212 <span class="keyword">char</span><span class="special">,</span> 2213 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">null_mutex_family</span><span class="special">>,</span> 2214 <span class="identifier">flat_map_index</span> 2215 <span class="special">></span> <span class="identifier">managed_heap_memory</span><span class="special">;</span> 2216 2217<span class="comment">//Named object creation managed memory segment</span> 2218<span class="comment">//All objects are constructed in a single buffer allocated via new[]</span> 2219<span class="comment">// Names are wide-strings,</span> 2220<span class="comment">// Default memory management algorithm</span> 2221<span class="comment">// (rbtree_best_fit with no mutexes and relative pointers)</span> 2222<span class="comment">// Name-object mappings are stored in the default index type (flat_map)</span> 2223<span class="keyword">typedef</span> <span class="identifier">basic_managed_heap_memory</span><span class="special"><</span> 2224 <span class="keyword">wchar_t</span><span class="special">,</span> 2225 <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">null_mutex_family</span><span class="special">>,</span> 2226 <span class="identifier">flat_map_index</span> 2227 <span class="special">></span> <span class="identifier">wmanaged_heap_memory</span><span class="special">;</span> 2228</pre> 2229<p> 2230 To use a managed heap memory, you must include the following header: 2231 </p> 2232<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_heap_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2233</pre> 2234<p> 2235 The use is exactly the same as <code class="computeroutput"><a class="link" href="../boost/interprocess/basic_ma_idm45304011784704.html" title="Class template basic_managed_external_buffer">basic_managed_external_buffer</a></code>, 2236 except that memory is created by the managed memory segment itself using 2237 dynamic (new/delete) memory. 2238 </p> 2239<p> 2240 <span class="bold"><strong>basic_managed_heap_memory</strong></span> also offers 2241 a <code class="computeroutput"><span class="identifier">grow</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">extra_bytes</span><span class="special">)</span></code> function that tries to resize internal 2242 heap memory so that we have room for more objects. But <span class="bold"><strong>be 2243 careful</strong></span>, if memory is reallocated, the old buffer will be copied 2244 into the new one so all the objects will be binary-copied to the new buffer. 2245 To be able to use this function, all pointers constructed in the heap buffer 2246 that point to objects in the heap buffer must be relative pointers (for 2247 example <code class="computeroutput"><span class="identifier">offset_ptr</span></code>). Otherwise, 2248 the result is undefined. Here is an example: 2249 </p> 2250<p> 2251</p> 2252<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">containers</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2253<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_heap_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2254<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 2255<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstddef</span><span class="special">></span> 2256 2257<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">;</span> 2258<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_heap_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> <span class="special">></span> 2259 <span class="identifier">MyList</span><span class="special">;</span> 2260 2261<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 2262<span class="special">{</span> 2263 <span class="comment">//We will create a buffer of 1000 bytes to store a list</span> 2264 <span class="identifier">managed_heap_memory</span> <span class="identifier">heap_memory</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 2265 2266 <span class="identifier">MyList</span> <span class="special">*</span> <span class="identifier">mylist</span> <span class="special">=</span> <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyList</span><span class="special">>(</span><span class="string">"MyList"</span><span class="special">)</span> 2267 <span class="special">(</span><span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 2268 2269 <span class="comment">//Obtain handle, that identifies the list in the buffer</span> 2270 <span class="identifier">managed_heap_memory</span><span class="special">::</span><span class="identifier">handle_t</span> <span class="identifier">list_handle</span> <span class="special">=</span> <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_handle_from_address</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">);</span> 2271 2272 <span class="comment">//Fill list until there is no more memory in the buffer</span> 2273 <span class="keyword">try</span><span class="special">{</span> 2274 <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{</span> 2275 <span class="identifier">mylist</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">-></span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span> 2276 <span class="special">}</span> 2277 <span class="special">}</span> 2278 <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bad_alloc</span> <span class="special">&){</span> 2279 <span class="comment">//memory is full</span> 2280 <span class="special">}</span> 2281 <span class="comment">//Let's obtain the size of the list</span> 2282 <span class="identifier">MyList</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">old_size</span> <span class="special">=</span> <span class="identifier">mylist</span><span class="special">-></span><span class="identifier">size</span><span class="special">();</span> 2283 2284 <span class="comment">//To make the list bigger, let's increase the heap buffer</span> 2285 <span class="comment">//in 1000 bytes more.</span> 2286 <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">grow</span><span class="special">(</span><span class="number">1000</span><span class="special">);</span> 2287 2288 <span class="comment">//If memory has been reallocated, the old pointer is invalid, so</span> 2289 <span class="comment">//use previously obtained handle to find the new pointer.</span> 2290 <span class="identifier">mylist</span> <span class="special">=</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">MyList</span> <span class="special">*></span> 2291 <span class="special">(</span><span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">get_address_from_handle</span><span class="special">(</span><span class="identifier">list_handle</span><span class="special">));</span> 2292 2293 <span class="comment">//Fill list until there is no more memory in the buffer</span> 2294 <span class="keyword">try</span><span class="special">{</span> 2295 <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{</span> 2296 <span class="identifier">mylist</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">-></span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span> 2297 <span class="special">}</span> 2298 <span class="special">}</span> 2299 <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bad_alloc</span> <span class="special">&){</span> 2300 <span class="comment">//memory is full</span> 2301 <span class="special">}</span> 2302 2303 <span class="comment">//Let's obtain the new size of the list</span> 2304 <span class="identifier">MyList</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">new_size</span> <span class="special">=</span> <span class="identifier">mylist</span><span class="special">-></span><span class="identifier">size</span><span class="special">();</span> 2305 2306 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">new_size</span> <span class="special">></span> <span class="identifier">old_size</span><span class="special">);</span> 2307 2308 <span class="comment">//Destroy list</span> 2309 <span class="identifier">heap_memory</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">mylist</span><span class="special">);</span> 2310 2311 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 2312<span class="special">}</span> 2313</pre> 2314<p> 2315 </p> 2316</div> 2317<div class="section"> 2318<div class="titlepage"><div><div><h4 class="title"> 2319<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.managed_heap_memory_external_buffer_diff" title="Differences between managed memory segments">Differences 2320 between managed memory segments</a> 2321</h4></div></div></div> 2322<p> 2323 All managed memory segments have similar capabilities (memory allocation 2324 inside the memory segment, named object construction...), but there are 2325 some remarkable differences between <span class="bold"><strong>managed_shared_memory</strong></span>, 2326 <span class="bold"><strong>managed_mapped_file</strong></span> and <span class="bold"><strong>managed_heap_memory</strong></span>, 2327 <span class="bold"><strong>managed_external_file</strong></span>. 2328 </p> 2329<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 2330<li class="listitem"> 2331 Default specializations of managed shared memory and mapped file use 2332 process-shared mutexes. Heap memory and external buffer have no internal 2333 synchronization by default. The cause is that the first two are thought 2334 to be shared between processes (although memory mapped files could 2335 be used just to obtain a persistent object data-base for a process) 2336 whereas the last two are thought to be used inside one process to construct 2337 a serialized named object data-base that can be sent though serial 2338 interprocess communications (like message queues, localhost network...). 2339 </li> 2340<li class="listitem"> 2341 The first two create a system-global object (a shared memory object 2342 or a file) shared by several processes, whereas the last two are objects 2343 that don't create system-wide resources. 2344 </li> 2345</ul></div> 2346</div> 2347<div class="section"> 2348<div class="titlepage"><div><div><h4 class="title"> 2349<a name="interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex"></a><a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_heap_memory_external_buffer.shared_message_queue_ex" title="Example: Serializing a database through the message queue">Example: 2350 Serializing a database through the message queue</a> 2351</h4></div></div></div> 2352<p> 2353 To see the utility of managed heap memory and managed external buffer classes, 2354 the following example shows how a message queue can be used to serialize 2355 a whole database constructed in a memory buffer using <span class="bold"><strong>Boost.Interprocess</strong></span>, 2356 send the database through a message queue and duplicated in another buffer: 2357 </p> 2358<p> 2359</p> 2360<pre class="programlisting"><span class="comment">//This test creates a in memory data-base using Interprocess machinery and</span> 2361<span class="comment">//serializes it through a message queue. Then rebuilds the data-base in</span> 2362<span class="comment">//another buffer and checks it against the original data-base</span> 2363<span class="keyword">bool</span> <span class="identifier">test_serialize_db</span><span class="special">()</span> 2364<span class="special">{</span> 2365 <span class="comment">//Typedef data to create a Interprocess map</span> 2366 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">MyPair</span><span class="special">;</span> 2367 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">MyLess</span><span class="special">;</span> 2368 <span class="keyword">typedef</span> <span class="identifier">node_allocator</span><span class="special"><</span><span class="identifier">MyPair</span><span class="special">,</span> <span class="identifier">managed_external_buffer</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 2369 <span class="identifier">node_allocator_t</span><span class="special">;</span> 2370 <span class="keyword">typedef</span> <span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> 2371 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> 2372 <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">>,</span> 2373 <span class="identifier">node_allocator_t</span><span class="special">></span> 2374 <span class="identifier">MyMap</span><span class="special">;</span> 2375 2376 <span class="comment">//Some constants</span> 2377 <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">BufferSize</span> <span class="special">=</span> <span class="number">65536</span><span class="special">;</span> 2378 <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxMsgSize</span> <span class="special">=</span> <span class="number">100</span><span class="special">;</span> 2379 2380 <span class="comment">//Allocate a memory buffer to hold the destiny database using vector<char></span> 2381 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">buffer_destiny</span><span class="special">(</span><span class="identifier">BufferSize</span><span class="special">,</span> <span class="number">0</span><span class="special">);</span> 2382 2383 <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span> 2384 <span class="special">{</span> 2385 <span class="comment">//Create the message-queues</span> 2386 <span class="identifier">message_queue</span> <span class="identifier">mq1</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">(),</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">MaxMsgSize</span><span class="special">);</span> 2387 2388 <span class="comment">//Open previously created message-queue simulating other process</span> 2389 <span class="identifier">message_queue</span> <span class="identifier">mq2</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span> 2390 2391 <span class="comment">//A managed heap memory to create the origin database</span> 2392 <span class="identifier">managed_heap_memory</span> <span class="identifier">db_origin</span><span class="special">(</span><span class="identifier">buffer_destiny</span><span class="special">.</span><span class="identifier">size</span><span class="special">());</span> 2393 2394 <span class="comment">//Construct the map in the first buffer</span> 2395 <span class="identifier">MyMap</span> <span class="special">*</span><span class="identifier">map1</span> <span class="special">=</span> <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyMap</span><span class="special">>(</span><span class="string">"MyMap"</span><span class="special">)</span> 2396 <span class="special">(</span><span class="identifier">MyLess</span><span class="special">(),</span> 2397 <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 2398 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">map1</span><span class="special">)</span> 2399 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 2400 2401 <span class="comment">//Fill map1 until is full</span> 2402 <span class="keyword">try</span><span class="special">{</span> 2403 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 2404 <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">){</span> 2405 <span class="special">(*</span><span class="identifier">map1</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> 2406 <span class="special">++</span><span class="identifier">i</span><span class="special">;</span> 2407 <span class="special">}</span> 2408 <span class="special">}</span> 2409 <span class="keyword">catch</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">bad_alloc</span> <span class="special">&){}</span> 2410 2411 <span class="comment">//Data control data sending through the message queue</span> 2412 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">sent</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 2413 <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">recvd</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 2414 <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">total_recvd</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 2415 <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">priority</span><span class="special">;</span> 2416 2417 <span class="comment">//Send whole first buffer through the mq1, read it</span> 2418 <span class="comment">//through mq2 to the second buffer</span> 2419 <span class="keyword">while</span><span class="special">(</span><span class="number">1</span><span class="special">){</span> 2420 <span class="comment">//Send a fragment of buffer1 through mq1</span> 2421 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_to_send</span> <span class="special">=</span> <span class="identifier">MaxMsgSize</span> <span class="special"><</span> <span class="special">(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">-</span> <span class="identifier">sent</span><span class="special">)</span> <span class="special">?</span> 2422 <span class="identifier">MaxMsgSize</span> <span class="special">:</span> <span class="special">(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_size</span><span class="special">()</span> <span class="special">-</span> <span class="identifier">sent</span><span class="special">);</span> 2423 <span class="identifier">mq1</span><span class="special">.</span><span class="identifier">send</span><span class="special">(</span> <span class="special">&</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>(</span><span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">get_address</span><span class="special">())[</span><span class="identifier">sent</span><span class="special">]</span> 2424 <span class="special">,</span> <span class="identifier">bytes_to_send</span> 2425 <span class="special">,</span> <span class="number">0</span><span class="special">);</span> 2426 <span class="identifier">sent</span> <span class="special">+=</span> <span class="identifier">bytes_to_send</span><span class="special">;</span> 2427 <span class="comment">//Receive the fragment through mq2 to buffer_destiny</span> 2428 <span class="identifier">mq2</span><span class="special">.</span><span class="identifier">receive</span><span class="special">(</span> <span class="special">&</span><span class="identifier">buffer_destiny</span><span class="special">[</span><span class="identifier">total_recvd</span><span class="special">]</span> 2429 <span class="special">,</span> <span class="identifier">BufferSize</span> <span class="special">-</span> <span class="identifier">recvd</span> 2430 <span class="special">,</span> <span class="identifier">recvd</span> 2431 <span class="special">,</span> <span class="identifier">priority</span><span class="special">);</span> 2432 <span class="identifier">total_recvd</span> <span class="special">+=</span> <span class="identifier">recvd</span><span class="special">;</span> 2433 2434 <span class="comment">//Check if we have received all the buffer</span> 2435 <span class="keyword">if</span><span class="special">(</span><span class="identifier">total_recvd</span> <span class="special">==</span> <span class="identifier">BufferSize</span><span class="special">){</span> 2436 <span class="keyword">break</span><span class="special">;</span> 2437 <span class="special">}</span> 2438 <span class="special">}</span> 2439 2440 <span class="comment">//The buffer will contain a copy of the original database</span> 2441 <span class="comment">//so let's interpret the buffer with managed_external_buffer</span> 2442 <span class="identifier">managed_external_buffer</span> <span class="identifier">db_destiny</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="special">&</span><span class="identifier">buffer_destiny</span><span class="special">[</span><span class="number">0</span><span class="special">],</span> <span class="identifier">BufferSize</span><span class="special">);</span> 2443 2444 <span class="comment">//Let's find the map</span> 2445 <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">MyMap</span> <span class="special">*,</span> <span class="identifier">managed_external_buffer</span><span class="special">::</span><span class="identifier">size_type</span><span class="special">></span> <span class="identifier">ret</span> <span class="special">=</span> <span class="identifier">db_destiny</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyMap</span><span class="special">>(</span><span class="string">"MyMap"</span><span class="special">);</span> 2446 <span class="identifier">MyMap</span> <span class="special">*</span><span class="identifier">map2</span> <span class="special">=</span> <span class="identifier">ret</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span> 2447 2448 <span class="comment">//Check if we have found it</span> 2449 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">map2</span><span class="special">){</span> 2450 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 2451 <span class="special">}</span> 2452 2453 <span class="comment">//Check if it is a single variable (not an array)</span> 2454 <span class="keyword">if</span><span class="special">(</span><span class="identifier">ret</span><span class="special">.</span><span class="identifier">second</span> <span class="special">!=</span> <span class="number">1</span><span class="special">){</span> 2455 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 2456 <span class="special">}</span> 2457 2458 <span class="comment">//Now let's compare size</span> 2459 <span class="keyword">if</span><span class="special">(</span><span class="identifier">map1</span><span class="special">-></span><span class="identifier">size</span><span class="special">()</span> <span class="special">!=</span> <span class="identifier">map2</span><span class="special">-></span><span class="identifier">size</span><span class="special">()){</span> 2460 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 2461 <span class="special">}</span> 2462 2463 <span class="comment">//Now let's compare all db values</span> 2464 <span class="identifier">MyMap</span><span class="special">::</span><span class="identifier">size_type</span> <span class="identifier">num_elements</span> <span class="special">=</span> <span class="identifier">map1</span><span class="special">-></span><span class="identifier">size</span><span class="special">();</span> 2465 <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">num_elements</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 2466 <span class="keyword">if</span><span class="special">((*</span><span class="identifier">map1</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">!=</span> <span class="special">(*</span><span class="identifier">map2</span><span class="special">)[</span><span class="identifier">i</span><span class="special">]){</span> 2467 <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> 2468 <span class="special">}</span> 2469 <span class="special">}</span> 2470 2471 <span class="comment">//Destroy maps from db-s</span> 2472 <span class="identifier">db_origin</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">map1</span><span class="special">);</span> 2473 <span class="identifier">db_destiny</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">map2</span><span class="special">);</span> 2474 <span class="special">}</span> 2475 <span class="identifier">message_queue</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">test</span><span class="special">::</span><span class="identifier">get_process_id_name</span><span class="special">());</span> 2476 <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 2477<span class="special">}</span> 2478</pre> 2479<p> 2480 </p> 2481</div> 2482</div> 2483</div> 2484<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 2485<td align="left"></td> 2486<td align="right"><div class="copyright-footer">Copyright © 2005-2015 Ion Gaztanaga<p> 2487 Distributed under the Boost Software License, Version 1.0. (See accompanying 2488 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 2489 </p> 2490</div></td> 2491</tr></table> 2492<hr> 2493<div class="spirit-nav"> 2494<a accesskey="p" href="synchronization_mechanisms.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../interprocess.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="allocators_containers.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 2495</div> 2496</body> 2497</html> 2498
