1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Allocators, containers and memory allocation algorithms</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../interprocess.html" title="Chapter 18. Boost.Interprocess"> 10<link rel="prev" href="managed_memory_segments.html" title="Managed Memory Segments"> 11<link rel="next" href="memory_algorithms.html" title="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="managed_memory_segments.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="memory_algorithms.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.allocators_containers"></a><a class="link" href="allocators_containers.html" title="Allocators, containers and memory allocation algorithms">Allocators, containers 29 and memory allocation algorithms</a> 30</h2></div></div></div> 31<div class="toc"><dl class="toc"> 32<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction">Introduction 33 to Interprocess allocators</a></span></dt> 34<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage">Segregated 35 storage node allocators</a></span></dt> 36<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive">Adaptive 37 pool node allocators</a></span></dt> 38<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained">Interprocess 39 and containers in managed memory segments</a></span></dt> 40<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers">Boost 41 containers compatible with Boost.Interprocess</a></span></dt> 42</dl></div> 43<div class="section"> 44<div class="titlepage"><div><div><h3 class="title"> 45<a name="interprocess.allocators_containers.allocator_introduction"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction" title="Introduction to Interprocess allocators">Introduction 46 to Interprocess allocators</a> 47</h3></div></div></div> 48<div class="toc"><dl class="toc"> 49<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties">Properties 50 of <span class="bold"><strong>Boost.Interprocess</strong></span> allocators</a></span></dt> 51<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_swapping">Swapping 52 Boost.Interprocess allocators</a></span></dt> 53<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator">allocator: 54 A general purpose allocator for managed memory segments</a></span></dt> 55</dl></div> 56<p> 57 As seen, <span class="bold"><strong>Boost.Interprocess</strong></span> offers raw memory 58 allocation and object construction using managed memory segments (managed 59 shared memory, managed mapped files...) and one of the first user requests 60 is the use of containers in managed shared memories. To achieve this, <span class="bold"><strong>Boost.Interprocess</strong></span> makes use of managed memory segment's 61 memory allocation algorithms to build several memory allocation schemes, 62 including general purpose and node allocators. 63 </p> 64<p> 65 <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators 66 are configurable via template parameters. Allocators define their <code class="computeroutput"><span class="identifier">pointer</span></code> typedef based on the <code class="computeroutput"><span class="identifier">void_pointer</span></code> typedef of the segment manager 67 passed as template argument. When this <code class="computeroutput"><span class="identifier">segment_manager</span><span class="special">::</span><span class="identifier">void_pointer</span></code> 68 is a relative pointer, (for example, <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code>) 69 the user can place these allocators in memory mapped in different base addresses 70 in several processes. 71 </p> 72<div class="section"> 73<div class="titlepage"><div><div><h4 class="title"> 74<a name="interprocess.allocators_containers.allocator_introduction.allocator_properties"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties 75 of <span class="bold"><strong>Boost.Interprocess</strong></span> allocators</a> 76</h4></div></div></div> 77<p> 78 Container allocators are normally default-constructible because the are 79 stateless. <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code> and <span class="bold"><strong>Boost.Pool's</strong></span> 80 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">pool_allocator</span></code>/<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fast_pool_allocator</span></code> 81 are examples of default-constructible allocators. 82 </p> 83<p> 84 On the other hand, <span class="bold"><strong>Boost.Interprocess</strong></span> 85 allocators need to allocate memory from a concrete memory segment and not 86 from a system-wide memory source (like the heap). <span class="bold"><strong>Boost.Interprocess</strong></span> 87 allocators are <span class="bold"><strong>stateful</strong></span>, which means that 88 they must be configured to tell them where the shared memory or the memory 89 mapped file is. 90 </p> 91<p> 92 This information is transmitted at compile-time and run-time: The allocators 93 receive a template parameter defining the type of the segment manager and 94 their constructor receive a pointer to the segment manager of the managed 95 memory segment where the user wants to allocate the values. 96 </p> 97<p> 98 <span class="bold"><strong>Boost.Interprocess</strong></span> allocators have <span class="bold"><strong>no default-constructors</strong></span> and containers must be explicitly 99 initialized with a configured allocator: 100 </p> 101<pre class="programlisting"><span class="comment">//The allocators must be templatized with the segment manager type</span> 102<span class="keyword">typedef</span> <span class="identifier">any_interprocess_allocator</span> 103 <span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">,</span> <span class="special">...></span> <span class="identifier">Allocator</span><span class="special">;</span> 104 105<span class="comment">//The allocator must be constructed with a pointer to the segment manager</span> 106<span class="identifier">Allocator</span> <span class="identifier">alloc_instance</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">(),</span> <span class="special">...);</span> 107 108<span class="comment">//Containers must be initialized with a configured allocator</span> 109<span class="keyword">typedef</span> <span class="identifier">my_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="identifier">MyIntList</span><span class="special">;</span> 110<span class="identifier">MyIntList</span> <span class="identifier">mylist</span><span class="special">(</span><span class="identifier">alloc_inst</span><span class="special">);</span> 111 112<span class="comment">//This would lead to a compilation error, because</span> 113<span class="comment">//the allocator has no default constructor</span> 114<span class="comment">//MyIntList mylist;</span> 115</pre> 116<p> 117 <span class="bold"><strong>Boost.Interprocess</strong></span> allocators also have 118 a <code class="computeroutput"><span class="identifier">get_segment_manager</span><span class="special">()</span></code> 119 function that returns the underlying segment manager that they have received 120 in the constructor: 121 </p> 122<pre class="programlisting"><span class="identifier">Allocator</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">alloc_instance</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">();</span> 123<span class="identifier">AnotherType</span> <span class="special">*</span><span class="identifier">a</span> <span class="special">=</span> <span class="identifier">s</span><span class="special">-></span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">AnotherType</span><span class="special">>(</span><span class="identifier">anonymous_instance</span><span class="special">)(/*</span><span class="identifier">Parameters</span><span class="special">*/);</span> 124</pre> 125</div> 126<div class="section"> 127<div class="titlepage"><div><div><h4 class="title"> 128<a name="interprocess.allocators_containers.allocator_introduction.allocator_swapping"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_swapping" title="Swapping Boost.Interprocess allocators">Swapping 129 Boost.Interprocess allocators</a> 130</h4></div></div></div> 131<p> 132 When swapping STL containers, there is an active discussion on what to 133 do with the allocators. Some STL implementations, for example Dinkumware 134 from Visual .NET 2003, perform a deep swap of the whole container through 135 a temporary when allocators are not equal. The <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n1599.html" target="_top">proposed 136 resolution</a> to container swapping is that allocators should be swapped 137 in a non-throwing way. 138 </p> 139<p> 140 Unfortunately, this approach is not valid with shared memory. Using heap 141 allocators, if Group1 of node allocators share a common segregated storage, 142 and Group2 share another common segregated storage, a simple pointer swapping 143 is needed to swap an allocator of Group1 and another allocator of Group2. 144 But when the user wants to swap two shared memory allocators, each one 145 placed in a different shared memory segment, this is not possible. As generally 146 shared memory is mapped in different addresses in each process, a pointer 147 placed in one segment can't point to any object placed in other shared 148 memory segment, since in each process, the distance between the segments 149 is different. However, if both shared memory allocators are in the same 150 segment, a non-throwing swap is possible, just like heap allocators. 151 </p> 152<p> 153 Until a final resolution is achieved. <span class="bold"><strong>Boost.Interprocess</strong></span> 154 allocators implement a non-throwing swap function that swaps internal pointers. 155 If an allocator placed in a shared memory segment is swapped with other 156 placed in a different shared memory segment, the result is undefined. But 157 a crash is quite sure. 158 </p> 159</div> 160<div class="section"> 161<div class="titlepage"><div><div><h4 class="title"> 162<a name="interprocess.allocators_containers.allocator_introduction.allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator" title="allocator: A general purpose allocator for managed memory segments">allocator: 163 A general purpose allocator for managed memory segments</a> 164</h4></div></div></div> 165<p> 166 The <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> 167 class defines an allocator class that uses the managed memory segment's 168 algorithm to allocate and deallocate memory. This is achieved through the 169 <span class="bold"><strong>segment manager</strong></span> of the managed memory 170 segment. This allocator is the equivalent for managed memory segments of 171 the standard <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code>. <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> 172 is templatized with the allocated type, and the segment manager. 173 </p> 174<p> 175 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> 176 instances constructed with the same segment manager compare equal. If an 177 instance is created using copy constructor, that instance compares equal 178 with the original one. 179 </p> 180<p> 181 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 182 deallocation are implemented as calls to the segment manager's allocation 183 function so the allocator offers the same thread-safety as the segment 184 manager. 185 </p> 186<p> 187 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> 188 you must include the following header: 189 </p> 190<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">allocators</span><span class="special">/</span><span class="identifier">allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 191</pre> 192<p> 193 <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> has 194 the following declaration: 195 </p> 196<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 197<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 198 199<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">></span> 200<span class="keyword">class</span> <span class="identifier">allocator</span><span class="special">;</span> 201 202<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 203<span class="special">}</span> <span class="comment">//namespace boost {</span> 204</pre> 205<p> 206 The allocator just provides the needed typedefs and forwards all allocation 207 and deallocation requests to the segment manager passed in the constructor, 208 just like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span></code> forwards the requests to <code class="computeroutput"><span class="keyword">operator</span> <span class="keyword">new</span><span class="special">[]</span></code>. 209 </p> 210<p> 211 Using <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">allocator</a></code> 212 is straightforward: 213 </p> 214<p> 215</p> 216<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> 217<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> 218<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 219 220<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> 221 222<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 223<span class="special">{</span> 224 <span class="comment">//Remove shared memory on construction and destruction</span> 225 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 226 <span class="special">{</span> 227 <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> 228 <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> 229 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 230 231 <span class="comment">//Create shared memory</span> 232 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 233 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 234 <span class="number">65536</span><span class="special">);</span> 235 236 <span class="comment">//Create an allocator that allocates ints from the managed segment</span> 237 <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 238 <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 239 240 <span class="comment">//Copy constructed allocator is equal</span> 241 <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 242 <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">);</span> 243 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance</span><span class="special">);</span> 244 245 <span class="comment">//Allocate and deallocate memory for 100 ints</span> 246 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</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="number">100</span><span class="special">);</span> 247 248 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 249<span class="special">}</span> 250</pre> 251<p> 252 </p> 253</div> 254</div> 255<div class="section"> 256<div class="titlepage"><div><div><h3 class="title"> 257<a name="interprocess.allocators_containers.stl_allocators_segregated_storage"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage" title="Segregated storage node allocators">Segregated 258 storage node allocators</a> 259</h3></div></div></div> 260<div class="toc"><dl class="toc"> 261<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common">Additional 262 parameters and functions of segregated storage node allocators</a></span></dt> 263<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator">node_allocator: 264 A process-shared segregated storage</a></span></dt> 265<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator">private_node_allocator: 266 a private segregated storage</a></span></dt> 267<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator">cached_node_allocator: 268 caching nodes to avoid overhead</a></span></dt> 269</dl></div> 270<p> 271 Variable size memory algorithms waste some space in management information 272 for each allocation. Sometimes, usually for small objects, this is not acceptable. 273 Memory algorithms can also fragment the managed memory segment under some 274 allocation and deallocation schemes, reducing their performance. When allocating 275 many objects of the same type, a simple segregated storage becomes a fast 276 and space-friendly allocator, as explained in the <a href="http://www.boost.org/libs/pool/" target="_top"><span class="bold"><strong>Boost.Pool</strong></span></a> library. 277 </p> 278<p> 279 Segregate storage node allocators allocate large memory chunks from a general 280 purpose memory allocator and divide that chunk into several nodes. No bookkeeping 281 information is stored in the nodes to achieve minimal memory waste: free 282 nodes are linked using a pointer constructed in the memory of the node. 283 </p> 284<p> 285 <span class="bold"><strong>Boost.Interprocess</strong></span> offers 3 allocators based 286 on this segregated storage algorithm: <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>, 287 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 288 and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>. 289 </p> 290<p> 291 To know the details of the implementation of of the segregated storage pools 292 see the <a class="link" href="architecture.html#interprocess.architecture.allocators_containers.implementation_segregated_storage_pools" title="Implementation of Boost.Interprocess segregated storage pools">Implementation 293 of <span class="bold"><strong>Boost.Interprocess</strong></span> segregated storage 294 pools</a> section. 295 </p> 296<div class="section"> 297<div class="titlepage"><div><div><h4 class="title"> 298<a name="interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.segregated_allocators_common" title="Additional parameters and functions of segregated storage node allocators">Additional 299 parameters and functions of segregated storage node allocators</a> 300</h4></div></div></div> 301<p> 302 <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>, 303 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 304 and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code> 305 implement the standard allocator interface and the functions explained 306 in the <a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties 307 of Boost.Interprocess allocators</a>. 308 </p> 309<p> 310 All these allocators are templatized by 3 parameters: 311 </p> 312<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 313<li class="listitem"> 314 <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">T</span></code>: 315 The type to be allocated. 316 </li> 317<li class="listitem"> 318 <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">SegmentManager</span></code>: 319 The type of the segment manager that will be passed in the constructor. 320 </li> 321<li class="listitem"> 322 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span></code>: 323 The number of nodes that a memory chunk will contain. This value will 324 define the size of the memory the pool will request to the segment 325 manager when the pool runs out of nodes. This parameter has a default 326 value. 327 </li> 328</ul></div> 329<p> 330 These allocators also offer the <code class="computeroutput"><span class="identifier">deallocate_free_chunks</span><span class="special">()</span></code> function. This function will traverse 331 all the memory chunks of the pool and will return to the managed memory 332 segment the free chunks of memory. If this function is not used, deallocating 333 the free chunks does not happen until the pool is destroyed so the only 334 way to return memory allocated by the pool to the segment before destructing 335 the pool is calling manually this function. This function is quite time-consuming 336 because it has quadratic complexity (O(N^2)). 337 </p> 338</div> 339<div class="section"> 340<div class="titlepage"><div><div><h4 class="title"> 341<a name="interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.node_allocator" title="node_allocator: A process-shared segregated storage">node_allocator: 342 A process-shared segregated storage</a> 343</h4></div></div></div> 344<p> 345 For heap-memory node allocators (like <span class="bold"><strong>Boost.Pool's</strong></span> 346 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fast_pool_allocator</span></code> usually a global, 347 thread-shared singleton pool is used for each node size. This is not possible 348 if you try to share a node allocator between processes. To achieve this 349 sharing <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 350 uses the segment manager's unique type allocation service (see <a class="link" href="managed_memory_segments.html#interprocess.managed_memory_segments.managed_memory_segment_features.unique" title="Unique instance construction">Unique 351 instance construction</a> section). 352 </p> 353<p> 354 In the initialization, a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 355 object searches this unique object in the segment. If it is not preset, 356 it builds one. This way, all <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 357 objects built inside a memory segment share a unique memory pool. 358 </p> 359<p> 360 The common segregated storage is not only shared between node_allocators 361 of the same type, but it is also shared between all node allocators that 362 allocate objects of the same size, for example, <span class="bold"><strong>node_allocator<uint32></strong></span> 363 and <span class="bold"><strong>node_allocator<float32></strong></span>. This 364 saves a lot of memory but also imposes an synchronization overhead for 365 each node allocation. 366 </p> 367<p> 368 The dynamically created common segregated storage integrates a reference 369 count so that a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 370 can know if any other <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 371 is attached to the same common segregated storage. When the last allocator 372 attached to the pool is destroyed, the pool is destroyed. 373 </p> 374<p> 375 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 376 instances constructed with the same segment manager compare equal. If an 377 instance is created using copy constructor, that instance compares equal 378 with the original one. 379 </p> 380<p> 381 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 382 deallocation are implemented as calls to the shared pool. The shared pool 383 offers the same synchronization guarantees as the segment manager. 384 </p> 385<p> 386 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>, 387 you must include the following header: 388 </p> 389<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">allocators</span><span class="special">/</span><span class="identifier">node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 390</pre> 391<p> 392 <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 393 has the following declaration: 394 </p> 395<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 396<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 397 398<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...></span> 399<span class="keyword">class</span> <span class="identifier">node_allocator</span><span class="special">;</span> 400 401<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 402<span class="special">}</span> <span class="comment">//namespace boost {</span> 403</pre> 404<p> 405 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code>: 406 </p> 407<p> 408</p> 409<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> 410<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">node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 411<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 412 413<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> 414 415<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 416<span class="special">{</span> 417 <span class="comment">//Remove shared memory on construction and destruction</span> 418 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 419 <span class="special">{</span> 420 <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> 421 <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> 422 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 423 424 <span class="comment">//Create shared memory</span> 425 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 426 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 427 <span class="number">65536</span><span class="special">);</span> 428 429 <span class="comment">//Create a node_allocator that allocates ints from the managed segment</span> 430 <span class="comment">//The number of chunks per segment is the default value</span> 431 <span class="keyword">typedef</span> <span class="identifier">node_allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 432 <span class="identifier">node_allocator_t</span><span class="special">;</span> 433 <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 434 435 <span class="comment">//Create another node_allocator. Since the segment manager address</span> 436 <span class="comment">//is the same, this node_allocator will be</span> 437 <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span> 438 <span class="comment">//nodes allocated by "allocator_instance"</span> 439 <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 440 441 <span class="comment">//Create another node_allocator using copy-constructor. This</span> 442 <span class="comment">//node_allocator will also be attached to the same pool</span> 443 <span class="identifier">node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 444 445 <span class="comment">//All allocators are equal</span> 446 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 447 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 448 449 <span class="comment">//So memory allocated with one can be deallocated with another</span> 450 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 451 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 452 453 <span class="comment">//The common pool will be destroyed here, since no allocator is</span> 454 <span class="comment">//attached to the pool</span> 455 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 456<span class="special">}</span> 457</pre> 458<p> 459 </p> 460</div> 461<div class="section"> 462<div class="titlepage"><div><div><h4 class="title"> 463<a name="interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.private_node_allocator" title="private_node_allocator: a private segregated storage">private_node_allocator: 464 a private segregated storage</a> 465</h4></div></div></div> 466<p> 467 As said, the node_allocator shares a common segregated storage between 468 node_allocators that allocate objects of the same size and this optimizes 469 memory usage. However, it needs a unique/named object construction feature 470 so that this sharing can be possible. Also imposes a synchronization overhead 471 per node allocation because of this share. Sometimes, the unique object 472 service is not available (for example, when building index types to implement 473 the named allocation service itself) or the synchronization overhead is 474 not acceptable. Many times the programmer wants to make sure that the pool 475 is destroyed when the allocator is destroyed, to free the memory as soon 476 as possible. 477 </p> 478<p> 479 So <span class="bold"><strong>private_node_allocator</strong></span> uses the same 480 segregated storage as <code class="computeroutput"><span class="identifier">node_allocator</span></code>, 481 but each <span class="bold"><strong>private_node_allocator</strong></span> has its 482 own segregated storage pool. No synchronization is used when allocating 483 nodes, so there is far less overhead for an operation that usually involves 484 just a few pointer operations when allocating and deallocating a node. 485 </p> 486<p> 487 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 488 instances <span class="bold"><strong>never</strong></span> compare equal. Memory 489 allocated with one allocator <span class="bold"><strong>can't</strong></span> be 490 deallocated with another one. 491 </p> 492<p> 493 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 494 deallocation are <span class="bold"><strong>not</strong></span> thread-safe. 495 </p> 496<p> 497 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>, 498 you must include the following header: 499 </p> 500<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">allocators</span><span class="special">/</span><span class="identifier">private_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 501</pre> 502<p> 503 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 504 has the following declaration: 505 </p> 506<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 507<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 508 509<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...></span> 510<span class="keyword">class</span> <span class="identifier">private_node_allocator</span><span class="special">;</span> 511 512<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 513<span class="special">}</span> <span class="comment">//namespace boost {</span> 514</pre> 515<p> 516 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code>: 517 </p> 518<p> 519</p> 520<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> 521<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">private_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 522<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 523 524<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> 525 526<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 527<span class="special">{</span> 528 <span class="comment">//Remove shared memory on construction and destruction</span> 529 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 530 <span class="special">{</span> 531 <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> 532 <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> 533 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 534 535 <span class="comment">//Create shared memory</span> 536 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 537 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 538 <span class="number">65536</span><span class="special">);</span> 539 540 <span class="comment">//Create a private_node_allocator that allocates ints from the managed segment</span> 541 <span class="comment">//The number of chunks per segment is the default value</span> 542 <span class="keyword">typedef</span> <span class="identifier">private_node_allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 543 <span class="identifier">private_node_allocator_t</span><span class="special">;</span> 544 <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 545 546 <span class="comment">//Create another private_node_allocator.</span> 547 <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 548 549 <span class="comment">//Although the segment manager address</span> 550 <span class="comment">//is the same, this private_node_allocator will have its own pool so</span> 551 <span class="comment">//"allocator_instance2" CAN'T deallocate nodes allocated by "allocator_instance".</span> 552 <span class="comment">//"allocator_instance2" is NOT equal to "allocator_instance"</span> 553 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">!=</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 554 555 <span class="comment">//Create another node_allocator using copy-constructor.</span> 556 <span class="identifier">private_node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 557 558 <span class="comment">//This allocator is also unequal to allocator_instance2</span> 559 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">!=</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 560 561 <span class="comment">//Pools are destroyed with the allocators</span> 562 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 563<span class="special">}</span> 564</pre> 565<p> 566 </p> 567</div> 568<div class="section"> 569<div class="titlepage"><div><div><h4 class="title"> 570<a name="interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_segregated_storage.cached_node_allocator" title="cached_node_allocator: caching nodes to avoid overhead">cached_node_allocator: 571 caching nodes to avoid overhead</a> 572</h4></div></div></div> 573<p> 574 The total node sharing of <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 575 can impose a high overhead for some applications and the minimal synchronization 576 overhead of <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 577 can impose a unacceptable memory waste for other applications. 578 </p> 579<p> 580 To solve this, <span class="bold"><strong>Boost.Interprocess</strong></span> offers 581 an allocator, <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>, 582 that allocates nodes from the common pool but caches some of them privately 583 so that following allocations have no synchronization overhead. When the 584 cache is full, the allocator returns some cached nodes to the common pool, 585 and those will be available to other allocators. 586 </p> 587<p> 588 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code> 589 instances constructed with the same segment manager compare equal. If an 590 instance is created using copy constructor, that instance compares equal 591 with the original one. 592 </p> 593<p> 594 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 595 deallocation are <span class="bold"><strong>not</strong></span> thread-safe. 596 </p> 597<p> 598 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>, 599 you must include the following header: 600 </p> 601<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">allocators</span><span class="special">/</span><span class="identifier">cached_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 602</pre> 603<p> 604 <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code> 605 has the following declaration: 606 </p> 607<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 608<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 609 610<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...></span> 611<span class="keyword">class</span> <span class="identifier">cached_node_allocator</span><span class="special">;</span> 612 613<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 614<span class="special">}</span> <span class="comment">//namespace boost {</span> 615</pre> 616<p> 617 A <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code> 618 instance and a <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 619 instance share the same pool if both instances receive the same template 620 parameters. This means that nodes returned to the shared pool by one of 621 them can be reused by the other. Please note that this does not mean that 622 both allocators compare equal, this is just information for programmers 623 that want to maximize the use of the pool. 624 </p> 625<p> 626 <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>, 627 offers additional functions to control the cache (the cache can be controlled 628 per instance): 629 </p> 630<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 631<li class="listitem"> 632 <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> 633 <span class="identifier">n</span><span class="special">)</span></code>: 634 Sets the maximum cached nodes limit. If cached nodes reach the limit, 635 some are returned to the shared pool. 636 </li> 637<li class="listitem"> 638 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_max_cached_nodes</span><span class="special">()</span> <span class="keyword">const</span></code>: 639 Returns the maximum cached nodes limit. 640 </li> 641<li class="listitem"> 642 <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate_cache</span><span class="special">()</span></code>: Returns the cached nodes to the 643 shared pool. 644 </li> 645</ul></div> 646<p> 647 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_node_allocator.html" title="Class template cached_node_allocator">cached_node_allocator</a></code>: 648 </p> 649<p> 650</p> 651<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> 652<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">cached_node_allocator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 653<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 654 655<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> 656 657<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 658<span class="special">{</span> 659 <span class="comment">//Remove shared memory on construction and destruction</span> 660 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 661 <span class="special">{</span> 662 <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> 663 <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> 664 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 665 666 <span class="comment">//Create shared memory</span> 667 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 668 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 669 <span class="number">65536</span><span class="special">);</span> 670 671 <span class="comment">//Create a cached_node_allocator that allocates ints from the managed segment</span> 672 <span class="comment">//The number of chunks per segment is the default value</span> 673 <span class="keyword">typedef</span> <span class="identifier">cached_node_allocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 674 <span class="identifier">cached_node_allocator_t</span><span class="special">;</span> 675 <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 676 677 <span class="comment">//The max cached nodes are configurable per instance</span> 678 <span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">3</span><span class="special">);</span> 679 680 <span class="comment">//Create another cached_node_allocator. Since the segment manager address</span> 681 <span class="comment">//is the same, this cached_node_allocator will be</span> 682 <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span> 683 <span class="comment">//nodes allocated by "allocator_instance"</span> 684 <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 685 686 <span class="comment">//The max cached nodes are configurable per instance</span> 687 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">5</span><span class="special">);</span> 688 689 <span class="comment">//Create another cached_node_allocator using copy-constructor. This</span> 690 <span class="comment">//cached_node_allocator will also be attached to the same pool</span> 691 <span class="identifier">cached_node_allocator_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 692 693 <span class="comment">//We can clear the cache</span> 694 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate_cache</span><span class="special">();</span> 695 696 <span class="comment">//All allocators are equal</span> 697 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 698 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 699 700 <span class="comment">//So memory allocated with one can be deallocated with another</span> 701 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 702 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 703 704 <span class="comment">//The common pool will be destroyed here, since no allocator is</span> 705 <span class="comment">//attached to the pool</span> 706 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 707<span class="special">}</span> 708</pre> 709<p> 710 </p> 711</div> 712</div> 713<div class="section"> 714<div class="titlepage"><div><div><h3 class="title"> 715<a name="interprocess.allocators_containers.stl_allocators_adaptive"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive" title="Adaptive pool node allocators">Adaptive 716 pool node allocators</a> 717</h3></div></div></div> 718<div class="toc"><dl class="toc"> 719<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common">Additional 720 parameters and functions of adaptive pool node allocators</a></span></dt> 721<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool">adaptive_pool: 722 a process-shared adaptive pool</a></span></dt> 723<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool">private_adaptive_pool: 724 a private adaptive pool</a></span></dt> 725<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool">cached_adaptive_pool: 726 Avoiding synchronization overhead</a></span></dt> 727</dl></div> 728<p> 729 Node allocators based on simple segregated storage algorithm are both space-efficient 730 and fast but they have a problem: they only can grow. Every allocated node 731 avoids any payload to store additional data and that leads to the following 732 limitation: when a node is deallocated, it's stored in a free list of nodes 733 but memory is not returned to the segment manager so a deallocated node can 734 be only reused by other containers using the same node pool. 735 </p> 736<p> 737 This behaviour can be problematic if several containers use <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">boost::interprocess::node_allocator</a></code> 738 to temporarily allocate a lot of objects but they end storing a few of them: 739 the node pool will be full of nodes that won't be reused wasting memory from 740 the segment. 741 </p> 742<p> 743 Adaptive pool based allocators trade some space (the overhead can be as low 744 as 1%) and performance (acceptable for many applications) with the ability 745 to return free chunks of nodes to the memory segment, so that they can be 746 used by any other container or managed object construction. To know the details 747 of the implementation of of "adaptive pools" see the <a class="link" href="architecture.html#interprocess.architecture.allocators_containers.implementation_adaptive_pools" title="Implementation of Boost.Interprocess adaptive pools">Implementation 748 of <span class="bold"><strong>Boost.Intrusive</strong></span> adaptive pools</a> 749 section. 750 </p> 751<p> 752 Like with segregated storage based node allocators, Boost.Interprocess offers 753 3 new allocators: <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>, 754 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>, 755 <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>. 756 </p> 757<div class="section"> 758<div class="titlepage"><div><div><h4 class="title"> 759<a name="interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_allocators_common" title="Additional parameters and functions of adaptive pool node allocators">Additional 760 parameters and functions of adaptive pool node allocators</a> 761</h4></div></div></div> 762<p> 763 <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>, 764 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code> 765 and <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code> 766 implement the standard allocator interface and the functions explained 767 in the <a class="link" href="allocators_containers.html#interprocess.allocators_containers.allocator_introduction.allocator_properties" title="Properties of Boost.Interprocess allocators">Properties 768 of Boost.Interprocess allocators</a>. 769 </p> 770<p> 771 All these allocators are templatized by 4 parameters: 772 </p> 773<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 774<li class="listitem"> 775 <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">T</span></code>: 776 The type to be allocated. 777 </li> 778<li class="listitem"> 779 <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">SegmentManager</span></code>: 780 The type of the segment manager that will be passed in the constructor. 781 </li> 782<li class="listitem"> 783 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span></code>: 784 The number of nodes that a memory chunk will contain. This value will 785 define the size of the memory the pool will request to the segment 786 manager when the pool runs out of nodes. This parameter has a default 787 value. 788 </li> 789<li class="listitem"> 790 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span></code>: 791 The maximum number of free chunks that the pool will hold. If this 792 limit is reached the pool returns the chunks to the segment manager. 793 This parameter has a default value. 794 </li> 795</ul></div> 796<p> 797 These allocators also offer the <code class="computeroutput"><span class="identifier">deallocate_free_chunks</span><span class="special">()</span></code> function. This function will traverse 798 all the memory chunks of the pool and will return to the managed memory 799 segment the free chunks of memory. This function is much faster than for 800 segregated storage allocators, because the adaptive pool algorithm offers 801 constant-time access to free chunks. 802 </p> 803</div> 804<div class="section"> 805<div class="titlepage"><div><div><h4 class="title"> 806<a name="interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.adaptive_pool" title="adaptive_pool: a process-shared adaptive pool">adaptive_pool: 807 a process-shared adaptive pool</a> 808</h4></div></div></div> 809<p> 810 Just like <code class="computeroutput"><a class="link" href="../boost/interprocess/node_allocator.html" title="Class template node_allocator">node_allocator</a></code> 811 a global, process-thread pool is used for each node size. In the initialization, 812 <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code> 813 searches the pool in the segment. If it is not preset, it builds one. The 814 adaptive pool, is created using a unique name. The adaptive pool it is 815 also shared between all node_allocators that allocate objects of the same 816 size, for example, <span class="bold"><strong>adaptive_pool<uint32></strong></span> 817 and <span class="bold"><strong>adaptive_pool<float32></strong></span>. 818 </p> 819<p> 820 The common adaptive pool is destroyed when all the allocators attached 821 to the pool are destroyed. 822 </p> 823<p> 824 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code> 825 instances constructed with the same segment manager compare equal. If an 826 instance is created using copy constructor, that instance compares equal 827 with the original one. 828 </p> 829<p> 830 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 831 deallocation are implemented as calls to the shared pool. The shared pool 832 offers the same synchronization guarantees as the segment manager. 833 </p> 834<p> 835 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>, 836 you must include the following header: 837 </p> 838<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">allocators</span><span class="special">/</span><span class="identifier">adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 839</pre> 840<p> 841 <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code> 842 has the following declaration: 843 </p> 844<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 845<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 846 847<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span> <span class="special">=</span> <span class="special">...></span> 848<span class="keyword">class</span> <span class="identifier">adaptive_pool</span><span class="special">;</span> 849 850<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 851<span class="special">}</span> <span class="comment">//namespace boost {</span> 852</pre> 853<p> 854 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code>: 855 </p> 856<p> 857</p> 858<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> 859<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">adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 860<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 861 862<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> 863 864<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 865<span class="special">{</span> 866 <span class="comment">//Remove shared memory on construction and destruction</span> 867 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 868 <span class="special">{</span> 869 <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> 870 <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> 871 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 872 873 <span class="comment">//Create shared memory</span> 874 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 875 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 876 <span class="number">65536</span><span class="special">);</span> 877 878 <span class="comment">//Create a adaptive_pool that allocates ints from the managed segment</span> 879 <span class="comment">//The number of chunks per segment is the default value</span> 880 <span class="keyword">typedef</span> <span class="identifier">adaptive_pool</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 881 <span class="identifier">adaptive_pool_t</span><span class="special">;</span> 882 <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 883 884 <span class="comment">//Create another adaptive_pool. Since the segment manager address</span> 885 <span class="comment">//is the same, this adaptive_pool will be</span> 886 <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span> 887 <span class="comment">//nodes allocated by "allocator_instance"</span> 888 <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 889 890 <span class="comment">//Create another adaptive_pool using copy-constructor. This</span> 891 <span class="comment">//adaptive_pool will also be attached to the same pool</span> 892 <span class="identifier">adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 893 894 <span class="comment">//All allocators are equal</span> 895 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 896 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 897 898 <span class="comment">//So memory allocated with one can be deallocated with another</span> 899 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 900 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 901 902 <span class="comment">//The common pool will be destroyed here, since no allocator is</span> 903 <span class="comment">//attached to the pool</span> 904 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 905<span class="special">}</span> 906</pre> 907<p> 908 </p> 909</div> 910<div class="section"> 911<div class="titlepage"><div><div><h4 class="title"> 912<a name="interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.private_adaptive_pool" title="private_adaptive_pool: a private adaptive pool">private_adaptive_pool: 913 a private adaptive pool</a> 914</h4></div></div></div> 915<p> 916 Just like <code class="computeroutput"><a class="link" href="../boost/interprocess/private_node_allocator.html" title="Class template private_node_allocator">private_node_allocator</a></code> 917 owns a private segregated storage pool, <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code> 918 owns its own adaptive pool. If the user wants to avoid the excessive node 919 allocation synchronization overhead in a container <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code> 920 is a good choice. 921 </p> 922<p> 923 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code> 924 instances <span class="bold"><strong>never</strong></span> compare equal. Memory 925 allocated with one allocator <span class="bold"><strong>can't</strong></span> be 926 deallocated with another one. 927 </p> 928<p> 929 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 930 deallocation are <span class="bold"><strong>not</strong></span> thread-safe. 931 </p> 932<p> 933 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>, 934 you must include the following header: 935 </p> 936<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">allocators</span><span class="special">/</span><span class="identifier">private_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 937</pre> 938<p> 939 <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code> 940 has the following declaration: 941 </p> 942<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 943<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 944 945<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeChunks</span> <span class="special">=</span> <span class="special">...></span> 946<span class="keyword">class</span> <span class="identifier">private_adaptive_pool</span><span class="special">;</span> 947 948<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 949<span class="special">}</span> <span class="comment">//namespace boost {</span> 950</pre> 951<p> 952 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/private_adaptive_pool.html" title="Class template private_adaptive_pool">private_adaptive_pool</a></code>: 953 </p> 954<p> 955</p> 956<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> 957<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">private_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 958<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 959 960<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> 961 962<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 963<span class="special">{</span> 964 <span class="comment">//Remove shared memory on construction and destruction</span> 965 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 966 <span class="special">{</span> 967 <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> 968 <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> 969 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 970 971 <span class="comment">//Create shared memory</span> 972 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 973 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 974 <span class="number">65536</span><span class="special">);</span> 975 976 <span class="comment">//Create a private_adaptive_pool that allocates ints from the managed segment</span> 977 <span class="comment">//The number of chunks per segment is the default value</span> 978 <span class="keyword">typedef</span> <span class="identifier">private_adaptive_pool</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 979 <span class="identifier">private_adaptive_pool_t</span><span class="special">;</span> 980 <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 981 982 <span class="comment">//Create another private_adaptive_pool.</span> 983 <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 984 985 <span class="comment">//Although the segment manager address</span> 986 <span class="comment">//is the same, this private_adaptive_pool will have its own pool so</span> 987 <span class="comment">//"allocator_instance2" CAN'T deallocate nodes allocated by "allocator_instance".</span> 988 <span class="comment">//"allocator_instance2" is NOT equal to "allocator_instance"</span> 989 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">!=</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 990 991 <span class="comment">//Create another adaptive_pool using copy-constructor.</span> 992 <span class="identifier">private_adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 993 994 <span class="comment">//This allocator is also unequal to allocator_instance2</span> 995 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">!=</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 996 997 <span class="comment">//Pools are destroyed with the allocators</span> 998 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 999<span class="special">}</span> 1000</pre> 1001<p> 1002 </p> 1003</div> 1004<div class="section"> 1005<div class="titlepage"><div><div><h4 class="title"> 1006<a name="interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.stl_allocators_adaptive.cached_adaptive_pool" title="cached_adaptive_pool: Avoiding synchronization overhead">cached_adaptive_pool: 1007 Avoiding synchronization overhead</a> 1008</h4></div></div></div> 1009<p> 1010 Adaptive pools have also a cached version. In this allocator the allocator 1011 caches some nodes to avoid the synchronization and bookkeeping overhead 1012 of the shared adaptive pool. <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code> 1013 allocates nodes from the common adaptive pool but caches some of them privately 1014 so that following allocations have no synchronization overhead. When the 1015 cache is full, the allocator returns some cached nodes to the common pool, 1016 and those will be available to other <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pools</a></code> 1017 or <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pools</a></code> 1018 of the same managed segment. 1019 </p> 1020<p> 1021 <span class="bold"><strong>Equality:</strong></span> Two <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code> 1022 instances constructed with the same segment manager compare equal. If an 1023 instance is created using copy constructor, that instance compares equal 1024 with the original one. 1025 </p> 1026<p> 1027 <span class="bold"><strong>Allocation thread-safety:</strong></span> Allocation and 1028 deallocation are <span class="bold"><strong>not</strong></span> thread-safe. 1029 </p> 1030<p> 1031 To use <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>, 1032 you must include the following header: 1033 </p> 1034<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">allocators</span><span class="special">/</span><span class="identifier">cached_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1035</pre> 1036<p> 1037 <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code> 1038 has the following declaration: 1039 </p> 1040<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 1041<span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> 1042 1043<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">SegmentManager</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">NodesPerChunk</span> <span class="special">=</span> <span class="special">...,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">MaxFreeNodes</span> <span class="special">=</span> <span class="special">...></span> 1044<span class="keyword">class</span> <span class="identifier">cached_adaptive_pool</span><span class="special">;</span> 1045 1046<span class="special">}</span> <span class="comment">//namespace interprocess {</span> 1047<span class="special">}</span> <span class="comment">//namespace boost {</span> 1048</pre> 1049<p> 1050 A <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code> 1051 instance and an <code class="computeroutput"><a class="link" href="../boost/interprocess/adaptive_pool.html" title="Class template adaptive_pool">adaptive_pool</a></code> 1052 instance share the same pool if both instances receive the same template 1053 parameters. This means that nodes returned to the shared pool by one of 1054 them can be reused by the other. Please note that this does not mean that 1055 both allocators compare equal, this is just information for programmers 1056 that want to maximize the use of the pool. 1057 </p> 1058<p> 1059 <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>, 1060 offers additional functions to control the cache (the cache can be controlled 1061 per instance): 1062 </p> 1063<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1064<li class="listitem"> 1065 <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> 1066 <span class="identifier">n</span><span class="special">)</span></code>: 1067 Sets the maximum cached nodes limit. If cached nodes reach the limit, 1068 some are returned to the shared pool. 1069 </li> 1070<li class="listitem"> 1071 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_max_cached_nodes</span><span class="special">()</span> <span class="keyword">const</span></code>: 1072 Returns the maximum cached nodes limit. 1073 </li> 1074<li class="listitem"> 1075 <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate_cache</span><span class="special">()</span></code>: Returns the cached nodes to the 1076 shared pool. 1077 </li> 1078</ul></div> 1079<p> 1080 An example using <code class="computeroutput"><a class="link" href="../boost/interprocess/cached_adaptive_pool.html" title="Class template cached_adaptive_pool">cached_adaptive_pool</a></code>: 1081 </p> 1082<p> 1083</p> 1084<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> 1085<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">cached_adaptive_pool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1086<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 1087 1088<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> 1089 1090<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1091<span class="special">{</span> 1092 <span class="comment">//Remove shared memory on construction and destruction</span> 1093 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1094 <span class="special">{</span> 1095 <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> 1096 <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> 1097 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1098 1099 <span class="comment">//Create shared memory</span> 1100 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 1101 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 1102 <span class="number">65536</span><span class="special">);</span> 1103 1104 <span class="comment">//Create a cached_adaptive_pool that allocates ints from the managed segment</span> 1105 <span class="comment">//The number of chunks per segment is the default value</span> 1106 <span class="keyword">typedef</span> <span class="identifier">cached_adaptive_pool</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 1107 <span class="identifier">cached_adaptive_pool_t</span><span class="special">;</span> 1108 <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1109 1110 <span class="comment">//The max cached nodes are configurable per instance</span> 1111 <span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">3</span><span class="special">);</span> 1112 1113 <span class="comment">//Create another cached_adaptive_pool. Since the segment manager address</span> 1114 <span class="comment">//is the same, this cached_adaptive_pool will be</span> 1115 <span class="comment">//attached to the same pool so "allocator_instance2" can deallocate</span> 1116 <span class="comment">//nodes allocated by "allocator_instance"</span> 1117 <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance2</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1118 1119 <span class="comment">//The max cached nodes are configurable per instance</span> 1120 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">set_max_cached_nodes</span><span class="special">(</span><span class="number">5</span><span class="special">);</span> 1121 1122 <span class="comment">//Create another cached_adaptive_pool using copy-constructor. This</span> 1123 <span class="comment">//cached_adaptive_pool will also be attached to the same pool</span> 1124 <span class="identifier">cached_adaptive_pool_t</span> <span class="identifier">allocator_instance3</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">);</span> 1125 1126 <span class="comment">//We can clear the cache</span> 1127 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate_cache</span><span class="special">();</span> 1128 1129 <span class="comment">//All allocators are equal</span> 1130 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance</span> <span class="special">==</span> <span class="identifier">allocator_instance2</span><span class="special">);</span> 1131 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">allocator_instance2</span> <span class="special">==</span> <span class="identifier">allocator_instance3</span><span class="special">);</span> 1132 1133 <span class="comment">//So memory allocated with one can be deallocated with another</span> 1134 <span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 1135 <span class="identifier">allocator_instance3</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">allocator_instance2</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="number">1</span><span class="special">);</span> 1136 1137 <span class="comment">//The common pool will be destroyed here, since no allocator is</span> 1138 <span class="comment">//attached to the pool</span> 1139 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1140<span class="special">}</span> 1141</pre> 1142<p> 1143 </p> 1144</div> 1145</div> 1146<div class="section"> 1147<div class="titlepage"><div><div><h3 class="title"> 1148<a name="interprocess.allocators_containers.containers_explained"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained" title="Interprocess and containers in managed memory segments">Interprocess 1149 and containers in managed memory segments</a> 1150</h3></div></div></div> 1151<div class="toc"><dl class="toc"> 1152<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.stl_container_requirements">Container 1153 requirements for Boost.Interprocess allocators</a></span></dt> 1154<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers">STL 1155 containers in managed memory segments</a></span></dt> 1156<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.where_allocate">Where 1157 is this being allocated?</a></span></dt> 1158<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_and_move">Move 1159 semantics in Interprocess containers</a></span></dt> 1160<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_of_containers">Containers 1161 of containers</a></span></dt> 1162</dl></div> 1163<div class="section"> 1164<div class="titlepage"><div><div><h4 class="title"> 1165<a name="interprocess.allocators_containers.containers_explained.stl_container_requirements"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.stl_container_requirements" title="Container requirements for Boost.Interprocess allocators">Container 1166 requirements for Boost.Interprocess allocators</a> 1167</h4></div></div></div> 1168<p> 1169 <span class="bold"><strong>Boost.Interprocess</strong></span> STL compatible allocators 1170 offer a STL compatible allocator interface and if they define their internal 1171 <span class="bold"><strong>pointer</strong></span> typedef as a relative pointer, 1172 they can be used to place STL containers in shared memory, memory mapped 1173 files or in a user defined memory segment. 1174 </p> 1175<p> 1176 However, as Scott Meyers mentions in his Effective STL book, Item 10, 1177 <span class="emphasis"><em>"Be aware of allocator conventions and restrictions"</em></span>: 1178 </p> 1179<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1180<li class="listitem"> 1181 <span class="emphasis"><em>"the Standard explicitly allows library implementers 1182 to assume that every allocator's pointer typedef is a synonym for T*"</em></span> 1183 </li> 1184<li class="listitem"> 1185 <span class="emphasis"><em>"the Standard says that an implementation of the STL 1186 is permitted to assume that all allocator objects of the same type 1187 are equivalent and always compare equal"</em></span> 1188 </li> 1189</ul></div> 1190<p> 1191 Obviously, if any STL implementation ignores pointer typedefs, no smart 1192 pointer can be used as allocator::pointer. If STL implementations assume 1193 all allocator objects of the same type compare equal, it will assume that 1194 two allocators, each one allocating from a different memory pool are equal, 1195 which is a complete disaster. 1196 </p> 1197<p> 1198 STL containers that we want to place in shared memory or memory mapped 1199 files with <span class="bold"><strong>Boost.Interprocess</strong></span> can't make 1200 any of these assumptions, so: 1201 </p> 1202<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1203<li class="listitem"> 1204 STL containers may not assume that memory allocated with an allocator 1205 can be deallocated with other allocators of the same type. All allocators 1206 objects must compare equal only if memory allocated with one object 1207 can be deallocated with the other one, and this can only tested with 1208 operator==() at run-time. 1209 </li> 1210<li class="listitem"> 1211 Containers' internal pointers should be of the type allocator::pointer 1212 and containers may not assume allocator::pointer is a raw pointer. 1213 </li> 1214<li class="listitem"> 1215 All objects must be constructed-destroyed via allocator::construct 1216 and allocator::destroy functions. 1217 </li> 1218</ul></div> 1219</div> 1220<div class="section"> 1221<div class="titlepage"><div><div><h4 class="title"> 1222<a name="interprocess.allocators_containers.containers_explained.containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers" title="STL containers in managed memory segments">STL 1223 containers in managed memory segments</a> 1224</h4></div></div></div> 1225<p> 1226 Unfortunately, many STL implementations use raw pointers for internal data 1227 and ignore allocator pointer typedefs and others suppose at some point 1228 that the allocator::typedef is T*. This is because in practice, there wasn't 1229 need of allocators with a pointer typedef different from T* for pooled/node 1230 memory allocators. 1231 </p> 1232<p> 1233 Until STL implementations handle allocator::pointer typedefs in a generic 1234 way, <span class="bold"><strong>Boost.Interprocess</strong></span> offers the following 1235 classes: 1236 </p> 1237<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1238 <span class="bold"><strong>boost:interprocess::vector</strong></span> is the 1239 implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code> 1240 ready to be used in managed memory segments like shared memory. To 1241 use it include: 1242 </li></ul></div> 1243<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1244</pre> 1245<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1246 <span class="bold"><strong>boost:interprocess::deque</strong></span> is the implementation 1247 of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">deque</span></code> ready to be used in managed 1248 memory segments like shared memory. To use it include: 1249 </li></ul></div> 1250<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">deque</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1251</pre> 1252<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1253 <code class="computeroutput">list</code> is the 1254 implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span></code> 1255 ready to be used in managed memory segments like shared memory. To 1256 use it include: 1257 </li></ul></div> 1258<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> 1259</pre> 1260<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1261 <code class="computeroutput">slist</code> is the 1262 implementation of SGI's <code class="computeroutput"><span class="identifier">slist</span></code> 1263 container (singly linked list) ready to be used in managed memory segments 1264 like shared memory. To use it include: 1265 </li></ul></div> 1266<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">slist</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1267</pre> 1268<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1269 <code class="computeroutput">set</code>/ <code class="computeroutput">multiset</code>/ <code class="computeroutput">map</code>/ <code class="computeroutput">multimap</code> 1270 family is the implementation of std::set/multiset/map/multimap family 1271 ready to be used in managed memory segments like shared memory. To 1272 use them include: 1273 </li></ul></div> 1274<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">set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1275<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">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1276</pre> 1277<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1278 <code class="computeroutput">flat_set</code>/ 1279 <code class="computeroutput">flat_multiset</code>/ 1280 <code class="computeroutput">flat_map</code>/ 1281 <code class="computeroutput">flat_multimap</code> 1282 classes are the adaptation and extension of Andrei Alexandrescu's famous 1283 AssocVector class from Loki library, ready for the shared memory. These 1284 classes offer the same functionality as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">set</span><span class="special">/</span><span class="identifier">multiset</span><span class="special">/</span><span class="identifier">map</span><span class="special">/</span><span class="identifier">multimap</span></code> 1285 implemented with an ordered vector, which has faster lookups than the 1286 standard ordered associative containers based on red-black trees, but 1287 slower insertions. To use it include: 1288 </li></ul></div> 1289<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">flat_set</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1290<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">flat_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1291</pre> 1292<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 1293 <code class="computeroutput">basic_string</code> 1294 is the implementation of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_string</span></code> 1295 ready to be used in managed memory segments like shared memory. It's 1296 implemented using a vector-like contiguous storage, so it has fast 1297 c string conversion and can be used with the <a class="link" href="streams.html#interprocess.streams.vectorstream" title="Formatting directly in your character vector: vectorstream">vectorstream</a> 1298 iostream formatting classes. To use it include: 1299 </li></ul></div> 1300<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">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1301</pre> 1302<p> 1303 All these containers have the same default arguments as standard containers 1304 and they can be used with other, non <span class="bold"><strong>Boost.Interprocess</strong></span> 1305 allocators (std::allocator, or boost::pool_allocator, for example). 1306 </p> 1307<p> 1308 To place any of these containers in managed memory segments, we must define 1309 the allocator template parameter with a <span class="bold"><strong>Boost.Interprocess</strong></span> 1310 allocator so that the container allocates the values in the managed memory 1311 segment. To place the container itself in shared memory, we construct it 1312 in the managed memory segment just like any other object with <span class="bold"><strong>Boost.Interprocess</strong></span>: 1313 </p> 1314<p> 1315</p> 1316<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1317<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> 1318<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> 1319 1320<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1321<span class="special">{</span> 1322 <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> 1323 <span class="comment">//Remove shared memory on construction and destruction</span> 1324 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1325 <span class="special">{</span> 1326 <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> 1327 <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> 1328 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1329 1330 <span class="comment">//A managed shared memory where we can construct objects</span> 1331 <span class="comment">//associated with a c-string</span> 1332 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> 1333 <span class="string">"MySharedMemory"</span><span class="special">,</span> <span class="comment">//segment name</span> 1334 <span class="number">65536</span><span class="special">);</span> 1335 1336 <span class="comment">//Alias an STL-like allocator of ints that allocates ints from the segment</span> 1337 <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">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 1338 <span class="identifier">ShmemAllocator</span><span class="special">;</span> 1339 1340 <span class="comment">//Alias a vector that uses the previous STL-like allocator</span> 1341 <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">ShmemAllocator</span><span class="special">></span> <span class="identifier">MyVector</span><span class="special">;</span> 1342 1343 <span class="keyword">int</span> <span class="identifier">initVal</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span><span class="number">0</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">5</span><span class="special">,</span> <span class="number">6</span> <span class="special">};</span> 1344 <span class="keyword">const</span> <span class="keyword">int</span> <span class="special">*</span><span class="identifier">begVal</span> <span class="special">=</span> <span class="identifier">initVal</span><span class="special">;</span> 1345 <span class="keyword">const</span> <span class="keyword">int</span> <span class="special">*</span><span class="identifier">endVal</span> <span class="special">=</span> <span class="identifier">initVal</span> <span class="special">+</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">initVal</span><span class="special">)/</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">initVal</span><span class="special">[</span><span class="number">0</span><span class="special">]);</span> 1346 1347 <span class="comment">//Initialize the STL-like allocator</span> 1348 <span class="keyword">const</span> <span class="identifier">ShmemAllocator</span> <span class="identifier">alloc_inst</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1349 1350 <span class="comment">//Construct the vector in the shared memory segment with the STL-like allocator</span> 1351 <span class="comment">//from a range of iterators</span> 1352 <span class="identifier">MyVector</span> <span class="special">*</span><span class="identifier">myvector</span> <span class="special">=</span> 1353 <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyVector</span><span class="special">></span> 1354 <span class="special">(</span><span class="string">"MyVector"</span><span class="special">)/*</span><span class="identifier">object</span> <span class="identifier">name</span><span class="special">*/</span> 1355 <span class="special">(</span><span class="identifier">begVal</span> <span class="comment">/*first ctor parameter*/</span><span class="special">,</span> 1356 <span class="identifier">endVal</span> <span class="comment">/*second ctor parameter*/</span><span class="special">,</span> 1357 <span class="identifier">alloc_inst</span> <span class="comment">/*third ctor parameter*/</span><span class="special">);</span> 1358 1359 <span class="comment">//Use vector as your want</span> 1360 <span class="identifier">std</span><span class="special">::</span><span class="identifier">sort</span><span class="special">(</span><span class="identifier">myvector</span><span class="special">-></span><span class="identifier">rbegin</span><span class="special">(),</span> <span class="identifier">myvector</span><span class="special">-></span><span class="identifier">rend</span><span class="special">());</span> 1361 <span class="comment">// . . .</span> 1362 <span class="comment">//When done, destroy and delete vector from the segment</span> 1363 <span class="identifier">segment</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">MyVector</span><span class="special">>(</span><span class="string">"MyVector"</span><span class="special">);</span> 1364 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1365<span class="special">}</span> 1366</pre> 1367<p> 1368 </p> 1369<p> 1370 These containers also show how easy is to create/modify an existing container 1371 making possible to place it in shared memory. 1372 </p> 1373</div> 1374<div class="section"> 1375<div class="titlepage"><div><div><h4 class="title"> 1376<a name="interprocess.allocators_containers.containers_explained.where_allocate"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.where_allocate" title="Where is this being allocated?">Where 1377 is this being allocated?</a> 1378</h4></div></div></div> 1379<p> 1380 <span class="bold"><strong>Boost.Interprocess</strong></span> containers are placed 1381 in shared memory/memory mapped files, etc... using two mechanisms <span class="bold"><strong>at the same time</strong></span>: 1382 </p> 1383<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1384<li class="listitem"> 1385 <span class="bold"><strong>Boost.Interprocess </strong></span><code class="computeroutput"><span class="identifier">construct</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special"><></span></code>... functions. These functions 1386 place a C++ object in the shared memory/memory mapped file. But this 1387 places only the object, but <span class="bold"><strong>not</strong></span> the 1388 memory that this object may allocate dynamically. 1389 </li> 1390<li class="listitem"> 1391 Shared memory allocators. These allow allocating shared memory/memory 1392 mapped file portions so that containers can allocate dynamically fragments 1393 of memory to store newly inserted elements. 1394 </li> 1395</ul></div> 1396<p> 1397 This means that to place any <span class="bold"><strong>Boost.Interprocess</strong></span> 1398 container (including <span class="bold"><strong>Boost.Interprocess</strong></span> 1399 strings) in shared memory or memory mapped files, containers <span class="bold"><strong>must</strong></span>: 1400 </p> 1401<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 1402<li class="listitem"> 1403 Define their template allocator parameter to a <span class="bold"><strong>Boost.Interprocess</strong></span> 1404 allocator. 1405 </li> 1406<li class="listitem"> 1407 Every container constructor must take the <span class="bold"><strong>Boost.Interprocess</strong></span> 1408 allocator as parameter. 1409 </li> 1410<li class="listitem"> 1411 You must use construct<>/find_or_construct<>... functions 1412 to place the container in the managed memory. 1413 </li> 1414</ul></div> 1415<p> 1416 If you do the first two points but you don't use <code class="computeroutput"><span class="identifier">construct</span><span class="special"><></span></code> or <code class="computeroutput"><span class="identifier">find_or_construct</span><span class="special"><></span></code> you are creating a container placed 1417 <span class="bold"><strong>only</strong></span> in your process but that allocates 1418 memory for contained types from shared memory/memory mapped file. 1419 </p> 1420<p> 1421 Let's see an example: 1422 </p> 1423<p> 1424</p> 1425<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> 1426<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1427<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">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1428<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> 1429 1430<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1431<span class="special">{</span> 1432 <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> 1433 <span class="comment">//Typedefs</span> 1434 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 1435 <span class="identifier">CharAllocator</span><span class="special">;</span> 1436 <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>,</span> <span class="identifier">CharAllocator</span><span class="special">></span> 1437 <span class="identifier">MyShmString</span><span class="special">;</span> 1438 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 1439 <span class="identifier">StringAllocator</span><span class="special">;</span> 1440 <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">StringAllocator</span><span class="special">></span> 1441 <span class="identifier">MyShmStringVector</span><span class="special">;</span> 1442 1443 <span class="comment">//Open shared memory</span> 1444 <span class="comment">//Remove shared memory on construction and destruction</span> 1445 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1446 <span class="special">{</span> 1447 <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> 1448 <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> 1449 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1450 1451 <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">10000</span><span class="special">);</span> 1452 1453 <span class="comment">//Create allocators</span> 1454 <span class="identifier">CharAllocator</span> <span class="identifier">charallocator</span> <span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1455 <span class="identifier">StringAllocator</span> <span class="identifier">stringallocator</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1456 1457 <span class="comment">//This string is in only in this process (the pointer pointing to the</span> 1458 <span class="comment">//buffer that will hold the text is not in shared memory).</span> 1459 <span class="comment">//But the buffer that will hold "this is my text" is allocated from</span> 1460 <span class="comment">//shared memory</span> 1461 <span class="identifier">MyShmString</span> <span class="identifier">mystring</span><span class="special">(</span><span class="identifier">charallocator</span><span class="special">);</span> 1462 <span class="identifier">mystring</span> <span class="special">=</span> <span class="string">"this is my text"</span><span class="special">;</span> 1463 1464 <span class="comment">//This vector is only in this process (the pointer pointing to the</span> 1465 <span class="comment">//buffer that will hold the MyShmString-s is not in shared memory).</span> 1466 <span class="comment">//But the buffer that will hold 10 MyShmString-s is allocated from</span> 1467 <span class="comment">//shared memory using StringAllocator. Since strings use a shared</span> 1468 <span class="comment">//memory allocator (CharAllocator) the 10 buffers that hold</span> 1469 <span class="comment">//"this is my text" text are also in shared memory.</span> 1470 <span class="identifier">MyShmStringVector</span> <span class="identifier">myvector</span><span class="special">(</span><span class="identifier">stringallocator</span><span class="special">);</span> 1471 <span class="identifier">myvector</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myvector</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">10</span><span class="special">,</span> <span class="identifier">mystring</span><span class="special">);</span> 1472 1473 <span class="comment">//This vector is fully constructed in shared memory. All pointers</span> 1474 <span class="comment">//buffers are constructed in the same shared memory segment</span> 1475 <span class="comment">//This vector can be safely accessed from other processes.</span> 1476 <span class="identifier">MyShmStringVector</span> <span class="special">*</span><span class="identifier">myshmvector</span> <span class="special">=</span> 1477 <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyShmStringVector</span><span class="special">>(</span><span class="string">"myshmvector"</span><span class="special">)(</span><span class="identifier">stringallocator</span><span class="special">);</span> 1478 <span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">10</span><span class="special">,</span> <span class="identifier">mystring</span><span class="special">);</span> 1479 1480 <span class="comment">//Destroy vector. This will free all strings that the vector contains</span> 1481 <span class="identifier">shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">);</span> 1482 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1483<span class="special">}</span> 1484</pre> 1485<p> 1486 </p> 1487</div> 1488<div class="section"> 1489<div class="titlepage"><div><div><h4 class="title"> 1490<a name="interprocess.allocators_containers.containers_explained.containers_and_move"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_and_move" title="Move semantics in Interprocess containers">Move 1491 semantics in Interprocess containers</a> 1492</h4></div></div></div> 1493<p> 1494 <span class="bold"><strong>Boost.Interprocess</strong></span> containers support 1495 move semantics, which means that the contents of a container can be moved 1496 from a container to another one, without any copying. The contents of the 1497 source container are transferred to the target container and the source 1498 container is left in default-constructed state. 1499 </p> 1500<p> 1501 When using containers of containers, we can also use move-semantics to 1502 insert objects in the container, avoiding unnecessary copies. 1503 </p> 1504<p> 1505 To transfer the contents of a container to another one, use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">()</span></code> 1506 function, as shown in the example. For more details about functions supporting 1507 move-semantics, see the reference section of Boost.Interprocess containers: 1508 </p> 1509<p> 1510</p> 1511<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> 1512<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1513<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">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1514<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> 1515<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 1516 1517<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1518<span class="special">{</span> 1519 <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> 1520 1521 <span class="comment">//Typedefs</span> 1522 <span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="identifier">SegmentManager</span><span class="special">;</span> 1523 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">SegmentManager</span><span class="special">></span> <span class="identifier">CharAllocator</span><span class="special">;</span> 1524 <span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> 1525 <span class="special">,</span><span class="identifier">CharAllocator</span><span class="special">></span> <span class="identifier">MyShmString</span><span class="special">;</span> 1526 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">SegmentManager</span><span class="special">></span> <span class="identifier">StringAllocator</span><span class="special">;</span> 1527 <span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">MyShmString</span><span class="special">,</span> <span class="identifier">StringAllocator</span><span class="special">></span> <span class="identifier">MyShmStringVector</span><span class="special">;</span> 1528 1529 <span class="comment">//Remove shared memory on construction and destruction</span> 1530 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1531 <span class="special">{</span> 1532 <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> 1533 <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> 1534 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1535 1536 <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">10000</span><span class="special">);</span> 1537 1538 <span class="comment">//Create allocators</span> 1539 <span class="identifier">CharAllocator</span> <span class="identifier">charallocator</span> <span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1540 <span class="identifier">StringAllocator</span> <span class="identifier">stringallocator</span><span class="special">(</span><span class="identifier">shm</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1541 1542 <span class="comment">//Create a vector of strings in shared memory.</span> 1543 <span class="identifier">MyShmStringVector</span> <span class="special">*</span><span class="identifier">myshmvector</span> <span class="special">=</span> 1544 <span class="identifier">shm</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyShmStringVector</span><span class="special">>(</span><span class="string">"myshmvector"</span><span class="special">)(</span><span class="identifier">stringallocator</span><span class="special">);</span> 1545 1546 <span class="comment">//Insert 50 strings in shared memory. The strings will be allocated</span> 1547 <span class="comment">//only once and no string copy-constructor will be called when inserting</span> 1548 <span class="comment">//strings, leading to a great performance.</span> 1549 <span class="identifier">MyShmString</span> <span class="identifier">string_to_compare</span><span class="special">(</span><span class="identifier">charallocator</span><span class="special">);</span> 1550 <span class="identifier">string_to_compare</span> <span class="special">=</span> <span class="string">"this is a long, long, long, long, long, long, string..."</span><span class="special">;</span> 1551 1552 <span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">reserve</span><span class="special">(</span><span class="number">50</span><span class="special">);</span> 1553 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</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">50</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 1554 <span class="identifier">MyShmString</span> <span class="identifier">move_me</span><span class="special">(</span><span class="identifier">string_to_compare</span><span class="special">);</span> 1555 <span class="comment">//In the following line, no string copy-constructor will be called.</span> 1556 <span class="comment">//"move_me"'s contents will be transferred to the string created in</span> 1557 <span class="comment">//the vector</span> 1558 <span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">push_back</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">move_me</span><span class="special">));</span> 1559 1560 <span class="comment">//The source string is in default constructed state</span> 1561 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">move_me</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span> 1562 1563 <span class="comment">//The newly created string will be equal to the "move_me"'s old contents</span> 1564 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">back</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">string_to_compare</span><span class="special">);</span> 1565 <span class="special">}</span> 1566 1567 <span class="comment">//Now erase a string...</span> 1568 <span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">pop_back</span><span class="special">();</span> 1569 1570 <span class="comment">//...And insert one in the first position.</span> 1571 <span class="comment">//No string copy-constructor or assignments will be called, but</span> 1572 <span class="comment">//move constructors and move-assignments. No memory allocation</span> 1573 <span class="comment">//function will be called in this operations!!</span> 1574 <span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">-></span><span class="identifier">begin</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">string_to_compare</span><span class="special">));</span> 1575 1576 <span class="comment">//Destroy vector. This will free all strings that the vector contains</span> 1577 <span class="identifier">shm</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">myshmvector</span><span class="special">);</span> 1578 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1579<span class="special">}</span> 1580</pre> 1581<p> 1582 </p> 1583</div> 1584<div class="section"> 1585<div class="titlepage"><div><div><h4 class="title"> 1586<a name="interprocess.allocators_containers.containers_explained.containers_of_containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.containers_explained.containers_of_containers" title="Containers of containers">Containers 1587 of containers</a> 1588</h4></div></div></div> 1589<p> 1590 When creating containers of containers, each container needs an allocator. 1591 To avoid using several allocators with complex type definitions, we can 1592 take advantage of the type erasure provided by void allocators and the 1593 ability to implicitly convert void allocators in allocators that allocate 1594 other types. 1595 </p> 1596<p> 1597 Here we have an example that builds a map in shared memory. Key is a string 1598 and the mapped type is a class that stores several containers: 1599 </p> 1600<p> 1601</p> 1602<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> 1603<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> 1604<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">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1605<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">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1606<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">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1607 1608<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> 1609 1610<span class="comment">//Typedefs of allocators and containers</span> 1611<span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="identifier">segment_manager_t</span><span class="special">;</span> 1612<span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">void</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">></span> <span class="identifier">void_allocator</span><span class="special">;</span> 1613<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">segment_manager_t</span><span class="special">></span> <span class="identifier">int_allocator</span><span class="special">;</span> 1614<span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">int_allocator</span><span class="special">></span> <span class="identifier">int_vector</span><span class="special">;</span> 1615<span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">int_vector</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">></span> <span class="identifier">int_vector_allocator</span><span class="special">;</span> 1616<span class="keyword">typedef</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">int_vector</span><span class="special">,</span> <span class="identifier">int_vector_allocator</span><span class="special">></span> <span class="identifier">int_vector_vector</span><span class="special">;</span> 1617<span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">></span> <span class="identifier">char_allocator</span><span class="special">;</span> 1618<span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>,</span> <span class="identifier">char_allocator</span><span class="special">></span> <span class="identifier">char_string</span><span class="special">;</span> 1619 1620<span class="keyword">class</span> <span class="identifier">complex_data</span> 1621<span class="special">{</span> 1622 <span class="keyword">int</span> <span class="identifier">id_</span><span class="special">;</span> 1623 <span class="identifier">char_string</span> <span class="identifier">char_string_</span><span class="special">;</span> 1624 <span class="identifier">int_vector_vector</span> <span class="identifier">int_vector_vector_</span><span class="special">;</span> 1625 1626 <span class="keyword">public</span><span class="special">:</span> 1627 <span class="comment">//Since void_allocator is convertible to any other allocator<T>, we can simplify</span> 1628 <span class="comment">//the initialization taking just one allocator for all inner containers.</span> 1629 <span class="identifier">complex_data</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">id</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">name</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">void_allocator</span> <span class="special">&</span><span class="identifier">void_alloc</span><span class="special">)</span> 1630 <span class="special">:</span> <span class="identifier">id_</span><span class="special">(</span><span class="identifier">id</span><span class="special">),</span> <span class="identifier">char_string_</span><span class="special">(</span><span class="identifier">name</span><span class="special">,</span> <span class="identifier">void_alloc</span><span class="special">),</span> <span class="identifier">int_vector_vector_</span><span class="special">(</span><span class="identifier">void_alloc</span><span class="special">)</span> 1631 <span class="special">{}</span> 1632 <span class="comment">//Other members...</span> 1633<span class="special">};</span> 1634 1635<span class="comment">//Definition of the map holding a string as key and complex_data as mapped type</span> 1636<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">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span><span class="special">></span> <span class="identifier">map_value_type</span><span class="special">;</span> 1637<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="identifier">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span><span class="special">></span> <span class="identifier">movable_to_map_value_type</span><span class="special">;</span> 1638<span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">map_value_type</span><span class="special">,</span> <span class="identifier">segment_manager_t</span><span class="special">></span> <span class="identifier">map_value_type_allocator</span><span class="special">;</span> 1639<span class="keyword">typedef</span> <span class="identifier">map</span><span class="special"><</span> <span class="identifier">char_string</span><span class="special">,</span> <span class="identifier">complex_data</span> 1640 <span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">char_string</span><span class="special">>,</span> <span class="identifier">map_value_type_allocator</span><span class="special">></span> <span class="identifier">complex_map_type</span><span class="special">;</span> 1641 1642<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1643<span class="special">{</span> 1644 <span class="comment">//Remove shared memory on construction and destruction</span> 1645 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1646 <span class="special">{</span> 1647 <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> 1648 <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> 1649 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1650 1651 <span class="comment">//Create shared memory</span> 1652 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</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> 1653 1654 <span class="comment">//An allocator convertible to any allocator<T, segment_manager_t> type</span> 1655 <span class="identifier">void_allocator</span> <span class="identifier">alloc_inst</span> <span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 1656 1657 <span class="comment">//Construct the shared memory map and fill it</span> 1658 <span class="identifier">complex_map_type</span> <span class="special">*</span><span class="identifier">mymap</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">complex_map_type</span><span class="special">></span> 1659 <span class="comment">//(object name), (first ctor parameter, second ctor parameter)</span> 1660 <span class="special">(</span><span class="string">"MyMap"</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">char_string</span><span class="special">>(),</span> <span class="identifier">alloc_inst</span><span class="special">);</span> 1661 1662 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</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">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 1663 <span class="comment">//Both key(string) and value(complex_data) need an allocator in their constructors</span> 1664 <span class="identifier">char_string</span> <span class="identifier">key_object</span><span class="special">(</span><span class="identifier">alloc_inst</span><span class="special">);</span> 1665 <span class="identifier">complex_data</span> <span class="identifier">mapped_object</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="string">"default_name"</span><span class="special">,</span> <span class="identifier">alloc_inst</span><span class="special">);</span> 1666 <span class="identifier">map_value_type</span> <span class="identifier">value</span><span class="special">(</span><span class="identifier">key_object</span><span class="special">,</span> <span class="identifier">mapped_object</span><span class="special">);</span> 1667 <span class="comment">//Modify values and insert them in the map</span> 1668 <span class="identifier">mymap</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">value</span><span class="special">);</span> 1669 <span class="special">}</span> 1670 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1671<span class="special">}</span> 1672</pre> 1673<p> 1674 </p> 1675</div> 1676</div> 1677<div class="section"> 1678<div class="titlepage"><div><div><h3 class="title"> 1679<a name="interprocess.allocators_containers.additional_containers"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers" title="Boost containers compatible with Boost.Interprocess">Boost 1680 containers compatible with Boost.Interprocess</a> 1681</h3></div></div></div> 1682<div class="toc"><dl class="toc"> 1683<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers.unordered">Boost 1684 unordered containers</a></span></dt> 1685<dt><span class="section"><a href="allocators_containers.html#interprocess.allocators_containers.additional_containers.multi_index">Boost.MultiIndex 1686 containers</a></span></dt> 1687</dl></div> 1688<p> 1689 As mentioned, container developers might need to change their implementation 1690 to make them compatible with Boost.Interprocess, because implementation usually 1691 ignore allocators with smart pointers. Hopefully several Boost containers 1692 are compatible with <span class="bold"><strong>Interprocess</strong></span>. 1693 </p> 1694<div class="section"> 1695<div class="titlepage"><div><div><h4 class="title"> 1696<a name="interprocess.allocators_containers.additional_containers.unordered"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers.unordered" title="Boost unordered containers">Boost 1697 unordered containers</a> 1698</h4></div></div></div> 1699<p> 1700 <span class="bold"><strong>Boost.Unordered</strong></span> containers are compatible 1701 with Interprocess, so programmers can store hash containers in shared memory 1702 and memory mapped files. Here is a small example storing <code class="computeroutput"><span class="identifier">unordered_map</span></code> in shared memory: 1703 </p> 1704<p> 1705</p> 1706<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> 1707<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> 1708 1709 1710<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">unordered_map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="comment">//boost::unordered_map</span> 1711 1712 1713<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">functional</span><span class="special">></span> <span class="comment">//std::equal_to</span> 1714<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">hash</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="comment">//boost::hash</span> 1715 1716 1717<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1718<span class="special">{</span> 1719 <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> 1720 <span class="comment">//Remove shared memory on construction and destruction</span> 1721 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1722 <span class="special">{</span> 1723 <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> 1724 <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> 1725 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1726 1727 <span class="comment">//Create shared memory</span> 1728 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</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> 1729 1730 <span class="comment">//Note that unordered_map<Key, MappedType>'s value_type is std::pair<const Key, MappedType>,</span> 1731 <span class="comment">//so the allocator must allocate that pair.</span> 1732 <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">KeyType</span><span class="special">;</span> 1733 <span class="keyword">typedef</span> <span class="keyword">float</span> <span class="identifier">MappedType</span><span class="special">;</span> 1734 <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="keyword">int</span><span class="special">,</span> <span class="keyword">float</span><span class="special">></span> <span class="identifier">ValueType</span><span class="special">;</span> 1735 1736 <span class="comment">//Typedef the allocator</span> 1737 <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">ValueType</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> <span class="identifier">ShmemAllocator</span><span class="special">;</span> 1738 1739 <span class="comment">//Alias an unordered_map of ints that uses the previous STL-like allocator.</span> 1740 <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_map</span> 1741 <span class="special"><</span> <span class="identifier">KeyType</span> <span class="special">,</span> <span class="identifier">MappedType</span> 1742 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span><span class="special"><</span><span class="identifier">KeyType</span><span class="special">></span> <span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">equal_to</span><span class="special"><</span><span class="identifier">KeyType</span><span class="special">></span> 1743 <span class="special">,</span> <span class="identifier">ShmemAllocator</span><span class="special">></span> 1744 <span class="identifier">MyHashMap</span><span class="special">;</span> 1745 1746 <span class="comment">//Construct a shared memory hash map.</span> 1747 <span class="comment">//Note that the first parameter is the initial bucket count and</span> 1748 <span class="comment">//after that, the hash function, the equality function and the allocator</span> 1749 <span class="identifier">MyHashMap</span> <span class="special">*</span><span class="identifier">myhashmap</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyHashMap</span><span class="special">>(</span><span class="string">"MyHashMap"</span><span class="special">)</span> <span class="comment">//object name</span> 1750 <span class="special">(</span> <span class="number">3</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">hash</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(),</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">equal_to</span><span class="special"><</span><span class="keyword">int</span><span class="special">>()</span> <span class="comment">//</span> 1751 <span class="special">,</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special"><</span><span class="identifier">ValueType</span><span class="special">>());</span> <span class="comment">//allocator instance</span> 1752 1753 <span class="comment">//Insert data in the hash map</span> 1754 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</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">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 1755 <span class="identifier">myhashmap</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">ValueType</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="special">(</span><span class="keyword">float</span><span class="special">)</span><span class="identifier">i</span><span class="special">));</span> 1756 <span class="special">}</span> 1757 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1758<span class="special">}</span> 1759</pre> 1760<p> 1761 </p> 1762</div> 1763<div class="section"> 1764<div class="titlepage"><div><div><h4 class="title"> 1765<a name="interprocess.allocators_containers.additional_containers.multi_index"></a><a class="link" href="allocators_containers.html#interprocess.allocators_containers.additional_containers.multi_index" title="Boost.MultiIndex containers">Boost.MultiIndex 1766 containers</a> 1767</h4></div></div></div> 1768<p> 1769 The widely used <span class="bold"><strong>Boost.MultiIndex</strong></span> library 1770 is compatible with <span class="bold"><strong>Boost.Interprocess</strong></span> 1771 so we can construct pretty good databases in shared memory. Constructing 1772 databases in shared memory is a bit tougher than in normal memory, usually 1773 because those databases contain strings and those strings need to be placed 1774 in shared memory. Shared memory strings require an allocator in their constructors 1775 so this usually makes object insertion a bit more complicated. 1776 </p> 1777<p> 1778 Here is an example that shows how to put a multi index container in shared 1779 memory: 1780 </p> 1781<p> 1782</p> 1783<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> 1784<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> 1785<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">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1786 1787 1788<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index_container</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1789<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index</span><span class="special">/</span><span class="identifier">member</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1790<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multi_index</span><span class="special">/</span><span class="identifier">ordered_index</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 1791 1792 1793<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> 1794<span class="keyword">namespace</span> <span class="identifier">bmi</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multi_index</span><span class="special">;</span> 1795 1796<span class="keyword">typedef</span> <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="keyword">char</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">char_allocator</span><span class="special">;</span> 1797<span class="keyword">typedef</span> <span class="identifier">basic_string</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>,</span> <span class="identifier">char_allocator</span><span class="special">></span><span class="identifier">shm_string</span><span class="special">;</span> 1798 1799<span class="comment">//Data to insert in shared memory</span> 1800<span class="keyword">struct</span> <span class="identifier">employee</span> 1801<span class="special">{</span> 1802 <span class="keyword">int</span> <span class="identifier">id</span><span class="special">;</span> 1803 <span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span> 1804 <span class="identifier">shm_string</span> <span class="identifier">name</span><span class="special">;</span> 1805 <span class="identifier">employee</span><span class="special">(</span> <span class="keyword">int</span> <span class="identifier">id_</span> 1806 <span class="special">,</span> <span class="keyword">int</span> <span class="identifier">age_</span> 1807 <span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">name_</span> 1808 <span class="special">,</span> <span class="keyword">const</span> <span class="identifier">char_allocator</span> <span class="special">&</span><span class="identifier">a</span><span class="special">)</span> 1809 <span class="special">:</span> <span class="identifier">id</span><span class="special">(</span><span class="identifier">id_</span><span class="special">),</span> <span class="identifier">age</span><span class="special">(</span><span class="identifier">age_</span><span class="special">),</span> <span class="identifier">name</span><span class="special">(</span><span class="identifier">name_</span><span class="special">,</span> <span class="identifier">a</span><span class="special">)</span> 1810 <span class="special">{}</span> 1811<span class="special">};</span> 1812 1813<span class="comment">//Tags</span> 1814<span class="keyword">struct</span> <span class="identifier">id</span><span class="special">{};</span> 1815<span class="keyword">struct</span> <span class="identifier">age</span><span class="special">{};</span> 1816<span class="keyword">struct</span> <span class="identifier">name</span><span class="special">{};</span> 1817 1818<span class="comment">// Define a multi_index_container of employees with following indices:</span> 1819<span class="comment">// - a unique index sorted by employee::int,</span> 1820<span class="comment">// - a non-unique index sorted by employee::name,</span> 1821<span class="comment">// - a non-unique index sorted by employee::age.</span> 1822<span class="keyword">typedef</span> <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">multi_index_container</span><span class="special"><</span> 1823 <span class="identifier">employee</span><span class="special">,</span> 1824 <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">indexed_by</span><span class="special"><</span> 1825 <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_unique</span> 1826 <span class="special"><</span><span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special"><</span><span class="identifier">id</span><span class="special">>,</span> <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">member</span><span class="special"><</span><span class="identifier">employee</span><span class="special">,</span><span class="keyword">int</span><span class="special">,&</span><span class="identifier">employee</span><span class="special">::</span><span class="identifier">id</span><span class="special">></span> <span class="special">>,</span> 1827 <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_non_unique</span><span class="special"><</span> 1828 <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special"><</span><span class="identifier">name</span><span class="special">>,</span> <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">member</span><span class="special"><</span><span class="identifier">employee</span><span class="special">,</span><span class="identifier">shm_string</span><span class="special">,&</span><span class="identifier">employee</span><span class="special">::</span><span class="identifier">name</span><span class="special">></span> <span class="special">>,</span> 1829 <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">ordered_non_unique</span> 1830 <span class="special"><</span><span class="identifier">bmi</span><span class="special">::</span><span class="identifier">tag</span><span class="special"><</span><span class="identifier">age</span><span class="special">>,</span> <span class="identifier">bmi</span><span class="special">::</span><span class="identifier">member</span><span class="special"><</span><span class="identifier">employee</span><span class="special">,</span><span class="keyword">int</span><span class="special">,&</span><span class="identifier">employee</span><span class="special">::</span><span class="identifier">age</span><span class="special">></span> <span class="special">></span> <span class="special">>,</span> 1831 <span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">allocator</span><span class="special"><</span><span class="identifier">employee</span><span class="special">>::</span><span class="identifier">type</span> 1832<span class="special">></span> <span class="identifier">employee_set</span><span class="special">;</span> 1833 1834<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 1835<span class="special">{</span> 1836 <span class="comment">//Remove shared memory on construction and destruction</span> 1837 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 1838 <span class="special">{</span> 1839 <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> 1840 <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> 1841 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 1842 1843 <span class="comment">//Create shared memory</span> 1844 <span class="identifier">managed_shared_memory</span> <span class="identifier">segment</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> 1845 1846 <span class="comment">//Construct the multi_index in shared memory</span> 1847 <span class="identifier">employee_set</span> <span class="special">*</span><span class="identifier">es</span> <span class="special">=</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">employee_set</span><span class="special">></span> 1848 <span class="special">(</span><span class="string">"My MultiIndex Container"</span><span class="special">)</span> <span class="comment">//Container's name in shared memory</span> 1849 <span class="special">(</span> <span class="identifier">employee_set</span><span class="special">::</span><span class="identifier">ctor_args_list</span><span class="special">()</span> 1850 <span class="special">,</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special"><</span><span class="identifier">employee</span><span class="special">>());</span> <span class="comment">//Ctor parameters</span> 1851 1852 <span class="comment">//Now insert elements</span> 1853 <span class="identifier">char_allocator</span> <span class="identifier">ca</span><span class="special">(</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">get_allocator</span><span class="special"><</span><span class="keyword">char</span><span class="special">>());</span> 1854 <span class="identifier">es</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">31</span><span class="special">,</span> <span class="string">"Joe"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span> 1855 <span class="identifier">es</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">27</span><span class="special">,</span> <span class="string">"Robert"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span> 1856 <span class="identifier">es</span><span class="special">-></span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">employee</span><span class="special">(</span><span class="number">2</span><span class="special">,</span><span class="number">40</span><span class="special">,</span> <span class="string">"John"</span><span class="special">,</span> <span class="identifier">ca</span><span class="special">));</span> 1857 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 1858<span class="special">}</span> 1859</pre> 1860<p> 1861 </p> 1862</div> 1863<p> 1864 Programmers can place <span class="bold"><strong>Boost.CircularBuffer</strong></span> 1865 containers in sharecd memory provided they disable debugging facilities with 1866 defines <code class="computeroutput"><span class="identifier">BOOST_CB_DISABLE_DEBUG</span></code> 1867 or the more general <code class="computeroutput"><span class="identifier">NDEBUG</span></code>. 1868 The reason is that those debugging facilities are only compatible with raw 1869 pointers. 1870 </p> 1871</div> 1872</div> 1873<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 1874<td align="left"></td> 1875<td align="right"><div class="copyright-footer">Copyright © 2005-2015 Ion Gaztanaga<p> 1876 Distributed under the Boost Software License, Version 1.0. (See accompanying 1877 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>) 1878 </p> 1879</div></td> 1880</tr></table> 1881<hr> 1882<div class="spirit-nav"> 1883<a accesskey="p" href="managed_memory_segments.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="memory_algorithms.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 1884</div> 1885</body> 1886</html> 1887
