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>Ownership smart pointers</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="streams.html" title="Direct iostream formatting: vectorstream and bufferstream"> 11<link rel="next" href="architecture.html" title="Architecture and internals"> 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="streams.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="architecture.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.interprocess_smart_ptr"></a><a class="link" href="interprocess_smart_ptr.html" title="Ownership smart pointers">Ownership smart pointers</a> 29</h2></div></div></div> 30<div class="toc"><dl class="toc"> 31<dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.intrusive_ptr">Intrusive 32 pointer</a></span></dt> 33<dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.scoped_ptr">Scoped 34 pointer</a></span></dt> 35<dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.shared_ptr">Shared 36 pointer and weak pointer</a></span></dt> 37<dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr">Unique 38 pointer</a></span></dt> 39</dl></div> 40<p> 41 C++ users know the importance of ownership smart pointers when dealing with 42 resources. Boost offers a wide range of such type of pointers: <code class="computeroutput"><span class="identifier">intrusive_ptr</span><span class="special"><></span></code>, 43 <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code>, 44 <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><></span></code>... 45 </p> 46<p> 47 When building complex shared memory/memory mapped files structures, programmers 48 would like to use also the advantages of these smart pointers. The problem 49 is that Boost and C++ TR1 smart pointers are not ready to be used for shared 50 memory. The cause is that those smart pointers contain raw pointers and they 51 use virtual functions, something that is not possible if you want to place 52 your data in shared memory. The virtual function limitation makes even impossible 53 to achieve the same level of functionality of Boost and TR1 with <span class="bold"><strong>Boost.Interprocess</strong></span> smart pointers. 54 </p> 55<p> 56 Interprocess ownership smart pointers are mainly "smart pointers containing 57 smart pointers", so we can specify the pointer type they contain. 58 </p> 59<div class="section"> 60<div class="titlepage"><div><div><h3 class="title"> 61<a name="interprocess.interprocess_smart_ptr.intrusive_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.intrusive_ptr" title="Intrusive pointer">Intrusive 62 pointer</a> 63</h3></div></div></div> 64<p> 65 <code class="computeroutput"><a class="link" href="../boost/interprocess/intrusive_ptr.html" title="Class template intrusive_ptr">boost::interprocess::intrusive_ptr</a></code> 66 is the generalization of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special"><></span></code> to allow non-raw pointers as intrusive 67 pointer members. As the well-known <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span></code> 68 we must specify the pointee type but we also must also specify the pointer 69 type to be stored in the intrusive_ptr: 70 </p> 71<pre class="programlisting"><span class="comment">//!The intrusive_ptr class template stores a pointer to an object</span> 72<span class="comment">//!with an embedded reference count. intrusive_ptr is parameterized on</span> 73<span class="comment">//!T (the type of the object pointed to) and VoidPointer(a void pointer type</span> 74<span class="comment">//!that defines the type of pointer that intrusive_ptr will store).</span> 75<span class="comment">//!intrusive_ptr<T, void *> defines a class with a T* member whereas</span> 76<span class="comment">//!intrusive_ptr<T, offset_ptr<void> > defines a class with a offset_ptr<T> member.</span> 77<span class="comment">//!Relies on unqualified calls to:</span> 78<span class="comment">//!</span> 79<span class="comment">//!void intrusive_ptr_add_ref(T * p);</span> 80<span class="comment">//!void intrusive_ptr_release(T * p);</span> 81<span class="comment">//!</span> 82<span class="comment">//!with (p != 0)</span> 83<span class="comment">//!</span> 84<span class="comment">//!The object is responsible for destroying itself.</span> 85<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">VoidPointer</span><span class="special">></span> 86<span class="keyword">class</span> <span class="identifier">intrusive_ptr</span><span class="special">;</span> 87</pre> 88<p> 89 So <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="keyword">void</span><span class="special">*></span></code> 90 is equivalent to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span></code>. 91 But if we want to place the intrusive_ptr in shared memory we must specify 92 a relative pointer type like <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">intrusive_ptr</span><span class="special"><</span><span class="identifier">MyClass</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">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> 93 <span class="special">></span></code> 94 </p> 95<p> 96</p> 97<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> 98<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">smart_ptr</span><span class="special">/</span><span class="identifier">intrusive_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 99 100<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> 101 102<span class="keyword">namespace</span> <span class="identifier">N</span> <span class="special">{</span> 103 104<span class="comment">//A class that has an internal reference count</span> 105<span class="keyword">class</span> <span class="identifier">reference_counted_class</span> 106<span class="special">{</span> 107 <span class="keyword">private</span><span class="special">:</span> 108 <span class="comment">//Non-copyable</span> 109 <span class="identifier">reference_counted_class</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">reference_counted_class</span> <span class="special">&);</span> 110 <span class="comment">//Non-assignable</span> 111 <span class="identifier">reference_counted_class</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">reference_counted_class</span> <span class="special">&);</span> 112 <span class="comment">//A typedef to save typing</span> 113 <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</span><span class="special">;</span> 114 <span class="comment">//This is the reference count</span> 115 <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">m_use_count</span><span class="special">;</span> 116 <span class="comment">//The segment manager allows deletion from shared memory segment</span> 117 <span class="identifier">offset_ptr</span><span class="special"><</span><span class="identifier">segment_manager</span><span class="special">></span> <span class="identifier">mp_segment_manager</span><span class="special">;</span> 118 119 <span class="keyword">public</span><span class="special">:</span> 120 <span class="comment">//Constructor</span> 121 <span class="identifier">reference_counted_class</span><span class="special">(</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">s_mngr</span><span class="special">)</span> 122 <span class="special">:</span> <span class="identifier">m_use_count</span><span class="special">(</span><span class="number">0</span><span class="special">),</span> <span class="identifier">mp_segment_manager</span><span class="special">(</span><span class="identifier">s_mngr</span><span class="special">){}</span> 123 <span class="comment">//Destructor</span> 124 <span class="special">~</span><span class="identifier">reference_counted_class</span><span class="special">(){}</span> 125 126 <span class="keyword">public</span><span class="special">:</span> 127 <span class="comment">//Returns the reference count</span> 128 <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">use_count</span><span class="special">()</span> <span class="keyword">const</span> 129 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">m_use_count</span><span class="special">;</span> <span class="special">}</span> 130 131 <span class="comment">//Adds a reference</span> 132 <span class="keyword">inline</span> <span class="keyword">friend</span> <span class="keyword">void</span> <span class="identifier">intrusive_ptr_add_ref</span><span class="special">(</span><span class="identifier">reference_counted_class</span> <span class="special">*</span> <span class="identifier">p</span><span class="special">)</span> 133 <span class="special">{</span> <span class="special">++</span><span class="identifier">p</span><span class="special">-></span><span class="identifier">m_use_count</span><span class="special">;</span> <span class="special">}</span> 134 135 <span class="comment">//Releases a reference</span> 136 <span class="keyword">inline</span> <span class="keyword">friend</span> <span class="keyword">void</span> <span class="identifier">intrusive_ptr_release</span><span class="special">(</span><span class="identifier">reference_counted_class</span> <span class="special">*</span> <span class="identifier">p</span><span class="special">)</span> 137 <span class="special">{</span> <span class="keyword">if</span><span class="special">(--</span><span class="identifier">p</span><span class="special">-></span><span class="identifier">m_use_count</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> <span class="identifier">p</span><span class="special">-></span><span class="identifier">mp_segment_manager</span><span class="special">-></span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">);</span> <span class="special">}</span> 138<span class="special">};</span> 139 140<span class="special">}</span> <span class="comment">//namespace N {</span> 141 142<span class="comment">//A class that has an intrusive pointer to reference_counted_class</span> 143<span class="keyword">class</span> <span class="identifier">intrusive_ptr_owner</span> 144<span class="special">{</span> 145 <span class="keyword">typedef</span> <span class="identifier">intrusive_ptr</span><span class="special"><</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span><span class="special">,</span> 146 <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">></span> <span class="identifier">intrusive_ptr_t</span><span class="special">;</span> 147 <span class="identifier">intrusive_ptr_t</span> <span class="identifier">m_intrusive_ptr</span><span class="special">;</span> 148 149 <span class="keyword">public</span><span class="special">:</span> 150 <span class="comment">//Takes a pointer to the reference counted class</span> 151 <span class="identifier">intrusive_ptr_owner</span><span class="special">(</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span> <span class="special">*</span><span class="identifier">ptr</span><span class="special">)</span> 152 <span class="special">:</span> <span class="identifier">m_intrusive_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">){}</span> 153<span class="special">};</span> 154 155<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 156<span class="special">{</span> 157 <span class="comment">//Remove shared memory on construction and destruction</span> 158 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 159 <span class="special">{</span> 160 <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> 161 <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> 162 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 163 164 <span class="comment">//Create shared memory</span> 165 <span class="identifier">managed_shared_memory</span> <span class="identifier">shmem</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> 166 167 <span class="comment">//Create the unique reference counted object in shared memory</span> 168 <span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span> <span class="special">*</span><span class="identifier">ref_counted</span> <span class="special">=</span> 169 <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">N</span><span class="special">::</span><span class="identifier">reference_counted_class</span><span class="special">></span> 170 <span class="special">(</span><span class="string">"ref_counted"</span><span class="special">)(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 171 172 <span class="comment">//Create an array of ten intrusive pointer owners in shared memory</span> 173 <span class="identifier">intrusive_ptr_owner</span> <span class="special">*</span><span class="identifier">intrusive_owner_array</span> <span class="special">=</span> 174 <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">intrusive_ptr_owner</span><span class="special">></span> 175 <span class="special">(</span><span class="identifier">anonymous_instance</span><span class="special">)[</span><span class="number">10</span><span class="special">](</span><span class="identifier">ref_counted</span><span class="special">);</span> 176 177 <span class="comment">//Now test that reference count is ten</span> 178 <span class="keyword">if</span><span class="special">(</span><span class="identifier">ref_counted</span><span class="special">-></span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">!=</span> <span class="number">10</span><span class="special">)</span> 179 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 180 181 <span class="comment">//Now destroy the array of intrusive pointer owners</span> 182 <span class="comment">//This should destroy every intrusive_ptr and because of</span> 183 <span class="comment">//that reference_counted_class will be destroyed</span> 184 <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">intrusive_owner_array</span><span class="special">);</span> 185 186 <span class="comment">//Now the reference counted object should have been destroyed</span> 187 <span class="keyword">if</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">intrusive_ptr_owner</span><span class="special">>(</span><span class="string">"ref_counted"</span><span class="special">).</span><span class="identifier">first</span><span class="special">)</span> 188 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 189 <span class="comment">//Success!</span> 190 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 191<span class="special">}</span> 192</pre> 193<p> 194 </p> 195</div> 196<div class="section"> 197<div class="titlepage"><div><div><h3 class="title"> 198<a name="interprocess.interprocess_smart_ptr.scoped_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.scoped_ptr" title="Scoped pointer">Scoped 199 pointer</a> 200</h3></div></div></div> 201<p> 202 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">scoped_ptr</span><span class="special"><></span></code> 203 is the big brother of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">scoped_ptr</span><span class="special"><></span></code>, which adds a custom deleter to specify 204 how the pointer passed to the scoped_ptr must be destroyed. Also, the <code class="computeroutput"><span class="identifier">pointer</span></code> typedef of the deleter will specify 205 the pointer type stored by scoped_ptr. 206 </p> 207<pre class="programlisting"><span class="comment">//!scoped_ptr stores a pointer to a dynamically allocated object.</span> 208<span class="comment">//!The object pointed to is guaranteed to be deleted, either on destruction</span> 209<span class="comment">//!of the scoped_ptr, or via an explicit reset. The user can avoid this</span> 210<span class="comment">//!deletion using release().</span> 211<span class="comment">//!scoped_ptr is parameterized on T (the type of the object pointed to) and</span> 212<span class="comment">//!Deleter (the functor to be executed to delete the internal pointer).</span> 213<span class="comment">//!The internal pointer will be of the same pointer type as typename</span> 214<span class="comment">//!Deleter::pointer type (that is, if typename Deleter::pointer is</span> 215<span class="comment">//!offset_ptr<void>, the internal pointer will be offset_ptr<T>).</span> 216<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">Deleter</span><span class="special">></span> 217<span class="keyword">class</span> <span class="identifier">scoped_ptr</span><span class="special">;</span> 218</pre> 219<p> 220 <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code> 221 comes handy to implement <span class="bold"><strong>rollbacks</strong></span> with 222 exceptions: if an exception is thrown or we call <code class="computeroutput"><span class="keyword">return</span></code> 223 in the scope of <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code> the deleter is automatically called 224 so that <span class="bold"><strong>the deleter can be considered as a rollback</strong></span> 225 function. If all goes well, we call <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code> member function to avoid rollback when 226 the <code class="computeroutput"><span class="identifier">scoped_ptr</span></code> goes out of 227 scope. 228 </p> 229<p> 230</p> 231<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> 232<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">smart_ptr</span><span class="special">/</span><span class="identifier">scoped_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 233 234<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> 235 236<span class="keyword">class</span> <span class="identifier">my_class</span> 237<span class="special">{};</span> 238 239<span class="keyword">class</span> <span class="identifier">my_exception</span> 240<span class="special">{};</span> 241 242<span class="comment">//A functor that destroys the shared memory object</span> 243<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 244<span class="keyword">class</span> <span class="identifier">my_deleter</span> 245<span class="special">{</span> 246 <span class="keyword">private</span><span class="special">:</span> 247 <span class="comment">//A typedef to save typing</span> 248 <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</span><span class="special">;</span> 249 <span class="comment">//This my_deleter is created in the stack, not in shared memory,</span> 250 <span class="comment">//so we can use raw pointers</span> 251 <span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">mp_segment_manager</span><span class="special">;</span> 252 253 <span class="keyword">public</span><span class="special">:</span> 254 <span class="comment">//This typedef will specify the pointer type that</span> 255 <span class="comment">//scoped_ptr will store</span> 256 <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">*</span><span class="identifier">pointer</span><span class="special">;</span> 257 <span class="comment">//Constructor</span> 258 <span class="identifier">my_deleter</span><span class="special">(</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">s_mngr</span><span class="special">)</span> 259 <span class="special">:</span> <span class="identifier">mp_segment_manager</span><span class="special">(</span><span class="identifier">s_mngr</span><span class="special">){}</span> 260 261 <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">pointer</span> <span class="identifier">object_to_delete</span><span class="special">)</span> 262 <span class="special">{</span> <span class="identifier">mp_segment_manager</span><span class="special">-></span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">object_to_delete</span><span class="special">);</span> <span class="special">}</span> 263<span class="special">};</span> 264 265<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 266<span class="special">{</span> 267 <span class="comment">//Create shared memory</span> 268 <span class="comment">//Remove shared memory on construction and destruction</span> 269 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 270 <span class="special">{</span> 271 <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> 272 <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> 273 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 274 275 <span class="identifier">managed_shared_memory</span> <span class="identifier">shmem</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> 276 277 <span class="comment">//In the first try, there will be no exceptions</span> 278 <span class="comment">//in the second try we will throw an exception</span> 279 <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">2</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> 280 <span class="comment">//Create an object in shared memory</span> 281 <span class="identifier">my_class</span> <span class="special">*</span> <span class="identifier">my_object</span> <span class="special">=</span> <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="string">"my_object"</span><span class="special">)();</span> 282 <span class="identifier">my_class</span> <span class="special">*</span> <span class="identifier">my_object2</span> <span class="special">=</span> <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="identifier">anonymous_instance</span><span class="special">)();</span> 283 <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">my_object2</span><span class="special">);</span> 284 285 <span class="comment">//Since the next shared memory allocation can throw</span> 286 <span class="comment">//assign it to a scoped_ptr so that if an exception occurs</span> 287 <span class="comment">//we destroy the object automatically</span> 288 <span class="identifier">my_deleter</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="identifier">d</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 289 290 <span class="keyword">try</span><span class="special">{</span> 291 <span class="identifier">scoped_ptr</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">,</span> <span class="identifier">my_deleter</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="special">></span> <span class="identifier">s_ptr</span><span class="special">(</span><span class="identifier">my_object</span><span class="special">,</span> <span class="identifier">d</span><span class="special">);</span> 292 <span class="comment">//Let's emulate a exception capable operation</span> 293 <span class="comment">//In the second try, throw an exception</span> 294 <span class="keyword">if</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">){</span> 295 <span class="keyword">throw</span><span class="special">(</span><span class="identifier">my_exception</span><span class="special">());</span> 296 <span class="special">}</span> 297 <span class="comment">//If we have passed the dangerous zone</span> 298 <span class="comment">//we can release the scoped pointer</span> 299 <span class="comment">//to avoid destruction</span> 300 <span class="identifier">s_ptr</span><span class="special">.</span><span class="identifier">release</span><span class="special">();</span> 301 <span class="special">}</span> 302 <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">my_exception</span> <span class="special">&){}</span> 303 <span class="comment">//Here, scoped_ptr is destroyed</span> 304 <span class="comment">//so it we haven't thrown an exception</span> 305 <span class="comment">//the object should be there, otherwise, destroyed</span> 306 <span class="keyword">if</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">){</span> 307 <span class="comment">//Make sure the object is alive</span> 308 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="string">"my_object"</span><span class="special">).</span><span class="identifier">first</span><span class="special">){</span> 309 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 310 <span class="special">}</span> 311 <span class="comment">//Now we can use it and delete it manually</span> 312 <span class="identifier">shmem</span><span class="special">.</span><span class="identifier">destroy</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="string">"my_object"</span><span class="special">);</span> 313 <span class="special">}</span> 314 <span class="keyword">else</span><span class="special">{</span> 315 <span class="comment">//Make sure the object has been deleted</span> 316 <span class="keyword">if</span><span class="special">(</span><span class="identifier">shmem</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">>(</span><span class="string">"my_object"</span><span class="special">).</span><span class="identifier">first</span><span class="special">){</span> 317 <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> 318 <span class="special">}</span> 319 <span class="special">}</span> 320 <span class="special">}</span> 321 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 322<span class="special">}</span> 323</pre> 324<p> 325 </p> 326</div> 327<div class="section"> 328<div class="titlepage"><div><div><h3 class="title"> 329<a name="interprocess.interprocess_smart_ptr.shared_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.shared_ptr" title="Shared pointer and weak pointer">Shared 330 pointer and weak pointer</a> 331</h3></div></div></div> 332<p> 333 <span class="bold"><strong>Boost.Interprocess</strong></span> also offers the possibility 334 of creating non-intrusive reference-counted objects in managed shared memory 335 or mapped files. 336 </p> 337<p> 338 Unlike <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a>, 339 due to limitations of mapped segments <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code> 340 cannot take advantage of virtual functions to maintain the same shared pointer 341 type while providing user-defined allocators and deleters. The allocator 342 and the deleter are template parameters of the shared pointer. 343 </p> 344<p> 345 Since the reference count and other auxiliary data needed by <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code> 346 must be created also in the managed segment, and the deleter has to delete 347 the object from the segment, the user must specify an allocator object and 348 a deleter object when constructing a non-empty instance of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>, 349 just like <span class="bold"><strong>Boost.Interprocess</strong></span> containers 350 need to pass allocators in their constructors. 351 </p> 352<p> 353 Here is the declaration of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>: 354 </p> 355<pre class="programlisting"><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">VoidAllocator</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Deleter</span><span class="special">></span> 356<span class="keyword">class</span> <span class="identifier">shared_ptr</span><span class="special">;</span> 357</pre> 358<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 359<li class="listitem"> 360 T is the type of the pointed type. 361 </li> 362<li class="listitem"> 363 VoidAllocator is the allocator to be used to allocate auxiliary elements 364 such as the reference count, the deleter... The internal <code class="computeroutput"><span class="identifier">pointer</span></code> typedef of the allocator will 365 determine the type of pointer that shared_ptr will internally use, so 366 allocators defining <code class="computeroutput"><span class="identifier">pointer</span></code> 367 as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> 368 will make all internal pointers used by <code class="computeroutput"><span class="identifier">shared_ptr</span></code> 369 to be also relative pointers. See <code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">boost::interprocess::allocator</a></code> 370 for a working allocator. 371 </li> 372<li class="listitem"> 373 Deleter is the function object that will be used to destroy the pointed 374 object when the last reference to the object is destroyed. The deleter 375 functor will take a pointer to T of the same category as the void pointer 376 defined by <code class="computeroutput"><span class="identifier">VoidAllocator</span><span class="special">::</span><span class="identifier">pointer</span></code>. 377 See <code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code> 378 for a generic deleter that erases a object from a managed segment. 379 </li> 380</ul></div> 381<p> 382 With correctly specified parameters, <span class="bold"><strong>Boost.Interprocess</strong></span> 383 users can create objects in shared memory that hold shared pointers pointing 384 to other objects also in shared memory, obtaining the benefits of reference 385 counting. Let's see how to create a shared pointer in a managed shared memory: 386 </p> 387<p> 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">managed_shared_memory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 390<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">smart_ptr</span><span class="special">/</span><span class="identifier">shared_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 391<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> 392<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">smart_ptr</span><span class="special">/</span><span class="identifier">deleter</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 393<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 394 395<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> 396 397<span class="comment">//This is type of the object we want to share</span> 398<span class="keyword">class</span> <span class="identifier">MyType</span> 399<span class="special">{};</span> 400 401<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_type</span><span class="special">;</span> 402<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_type</span><span class="special">></span> <span class="identifier">void_allocator_type</span><span class="special">;</span> 403<span class="keyword">typedef</span> <span class="identifier">deleter</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">segment_manager_type</span><span class="special">></span> <span class="identifier">deleter_type</span><span class="special">;</span> 404<span class="keyword">typedef</span> <span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">void_allocator_type</span><span class="special">,</span> <span class="identifier">deleter_type</span><span class="special">></span> <span class="identifier">my_shared_ptr</span><span class="special">;</span> 405 406<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 407<span class="special">{</span> 408 <span class="comment">//Remove shared memory on construction and destruction</span> 409 <span class="keyword">struct</span> <span class="identifier">shm_remove</span> 410 <span class="special">{</span> 411 <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> 412 <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> 413 <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> 414 415 <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">4096</span><span class="special">);</span> 416 417 <span class="comment">//Create a shared pointer in shared memory</span> 418 <span class="comment">//pointing to a newly created object in the segment</span> 419 <span class="identifier">my_shared_ptr</span> <span class="special">&</span><span class="identifier">shared_ptr_instance</span> <span class="special">=</span> 420 <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">my_shared_ptr</span><span class="special">>(</span><span class="string">"shared ptr"</span><span class="special">)</span> 421 <span class="comment">//Arguments to construct the shared pointer</span> 422 <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">MyType</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">)()</span> <span class="comment">//object to own</span> 423 <span class="special">,</span> <span class="identifier">void_allocator_type</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="comment">//allocator</span> 424 <span class="special">,</span> <span class="identifier">deleter_type</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="comment">//deleter</span> 425 <span class="special">);</span> 426 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">shared_ptr_instance</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 427 428 <span class="comment">//Destroy "shared ptr". "object to share" will be automatically destroyed</span> 429 <span class="identifier">segment</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(&</span><span class="identifier">shared_ptr_instance</span><span class="special">);</span> 430 431 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 432<span class="special">}</span> 433</pre> 434<p> 435 </p> 436<p> 437 <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code> 438 is very flexible and configurable (we can specify the allocator and the deleter, 439 for example), but as shown the creation of a shared pointer in managed segments 440 need too much typing. 441 </p> 442<p> 443 To simplify this usage, <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code> 444 header offers a shared pointer definition helper class (<code class="computeroutput"><a class="link" href="../boost/interprocess/managed_shared_ptr.html" title="Struct template managed_shared_ptr">managed_shared_ptr</a></code>) 445 and a function (<code class="computeroutput"><a class="link" href="../boost/interprocess/make_man_idm45304010749088.html" title="Function template make_managed_shared_ptr">make_managed_shared_ptr</a></code>) 446 to easily construct a shared pointer from a type allocated in a managed segment 447 with an allocator that will allocate the reference count also in the managed 448 segment and a deleter that will erase the object from the segment. 449 </p> 450<p> 451 These utilities will use a <span class="bold"><strong>Boost.Interprocess</strong></span> 452 allocator (<code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">boost::interprocess::allocator</a></code>) 453 and deleter (<code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code>) 454 to do their job. The definition of the previous shared pointer could be simplified 455 to the following: 456 </p> 457<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">managed_shared_ptr</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">managed_shared_memory</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">my_shared_ptr</span><span class="special">;</span> 458</pre> 459<p> 460 And the creation of a shared pointer can be simplified to this: 461 </p> 462<pre class="programlisting"><span class="identifier">my_shared_ptr</span> <span class="identifier">sh_ptr</span> <span class="special">=</span> <span class="identifier">make_managed_shared_ptr</span> 463 <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">MyType</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">)(),</span> <span class="identifier">segment</span><span class="special">);</span> 464</pre> 465<p> 466 <span class="bold"><strong>Boost.Interprocess</strong></span> also offers a weak pointer 467 named <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> 468 (with its corresponding <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_weak_ptr.html" title="Struct template managed_weak_ptr">managed_weak_ptr</a></code> 469 and <code class="computeroutput"><a class="link" href="../boost/interprocess/make_managed_weak_ptr.html" title="Function template make_managed_weak_ptr">make_managed_weak_ptr</a></code> 470 utilities) to implement non-owning observers of an object owned by <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>. 471 </p> 472<p> 473 Now let's see a detailed example of the use of <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code>: 474 and <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> 475 </p> 476<p> 477</p> 478<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 479<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">smart_ptr</span><span class="special">/</span><span class="identifier">shared_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 480<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">smart_ptr</span><span class="special">/</span><span class="identifier">weak_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 481<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 482 483<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> 484 485<span class="comment">//This is type of the object we want to share</span> 486<span class="keyword">struct</span> <span class="identifier">type_to_share</span> 487<span class="special">{};</span> 488 489<span class="comment">//This is the type of a shared pointer to the previous type</span> 490<span class="comment">//that will be built in the mapped file</span> 491<span class="keyword">typedef</span> <span class="identifier">managed_shared_ptr</span><span class="special"><</span><span class="identifier">type_to_share</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">shared_ptr_type</span><span class="special">;</span> 492<span class="keyword">typedef</span> <span class="identifier">managed_weak_ptr</span><span class="special"><</span><span class="identifier">type_to_share</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">weak_ptr_type</span><span class="special">;</span> 493 494<span class="comment">//This is a type holding a shared pointer</span> 495<span class="keyword">struct</span> <span class="identifier">shared_ptr_owner</span> 496<span class="special">{</span> 497 <span class="identifier">shared_ptr_owner</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">shared_ptr_type</span> <span class="special">&</span><span class="identifier">other_shared_ptr</span><span class="special">)</span> 498 <span class="special">:</span> <span class="identifier">shared_ptr_</span><span class="special">(</span><span class="identifier">other_shared_ptr</span><span class="special">)</span> 499 <span class="special">{}</span> 500 501 <span class="identifier">shared_ptr_owner</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">shared_ptr_owner</span> <span class="special">&</span><span class="identifier">other_owner</span><span class="special">)</span> 502 <span class="special">:</span> <span class="identifier">shared_ptr_</span><span class="special">(</span><span class="identifier">other_owner</span><span class="special">.</span><span class="identifier">shared_ptr_</span><span class="special">)</span> 503 <span class="special">{}</span> 504 505 <span class="identifier">shared_ptr_type</span> <span class="identifier">shared_ptr_</span><span class="special">;</span> 506 <span class="comment">//...</span> 507<span class="special">};</span> 508 509<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 510<span class="special">{</span> 511 <span class="comment">//Define file names</span> 512 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span> <span class="special">=</span> <span class="string">"MyMappedFile"</span><span class="special">;</span> 513 514 <span class="comment">//Destroy any previous file with the name to be used.</span> 515 <span class="keyword">struct</span> <span class="identifier">file_remove</span> 516 <span class="special">{</span> 517 <span class="identifier">file_remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span><span class="special">)</span> 518 <span class="special">:</span> <span class="identifier">MappedFile_</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span> 519 <span class="special">~</span><span class="identifier">file_remove</span><span class="special">(){</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span> 520 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile_</span><span class="special">;</span> 521 <span class="special">}</span> <span class="identifier">remover</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">);</span> 522 <span class="special">{</span> 523 <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 524 525 <span class="comment">//Construct the shared type in the file and</span> 526 <span class="comment">//pass ownership to this local shared pointer</span> 527 <span class="identifier">shared_ptr_type</span> <span class="identifier">local_shared_ptr</span> <span class="special">=</span> <span class="identifier">make_managed_shared_ptr</span> 528 <span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">type_to_share</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">)(),</span> <span class="identifier">file</span><span class="special">);</span> 529 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 530 531 <span class="comment">//Share ownership of the object between local_shared_ptr and a new "owner1"</span> 532 <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner1</span> <span class="special">=</span> 533 <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">shared_ptr_owner</span><span class="special">>(</span><span class="string">"owner1"</span><span class="special">)(</span><span class="identifier">local_shared_ptr</span><span class="special">);</span> 534 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 535 536 <span class="comment">//local_shared_ptr releases object ownership</span> 537 <span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> 538 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 539 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 540 541 <span class="comment">//Share ownership of the object between "owner1" and a new "owner2"</span> 542 <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner2</span> <span class="special">=</span> 543 <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">shared_ptr_owner</span><span class="special">>(</span><span class="string">"owner2"</span><span class="special">)(*</span><span class="identifier">owner1</span><span class="special">);</span> 544 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 545 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 546 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> 547 <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk</span> 548 <span class="special">}</span> 549 <span class="special">{</span> 550 <span class="comment">//Reopen the mapped file and find again all owners</span> 551 <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">);</span> 552 553 <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner1</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">shared_ptr_owner</span><span class="special">>(</span><span class="string">"owner1"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span> 554 <span class="identifier">shared_ptr_owner</span> <span class="special">*</span><span class="identifier">owner2</span> <span class="special">=</span> <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">shared_ptr_owner</span><span class="special">>(</span><span class="string">"owner2"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span> 555 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span> <span class="special">&&</span> <span class="identifier">owner2</span><span class="special">);</span> 556 557 <span class="comment">//Check everything is as expected</span> 558 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">type_to_share</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 559 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 560 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 561 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> 562 563 <span class="comment">//Now destroy one of the owners, the reference count drops.</span> 564 <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">owner1</span><span class="special">);</span> 565 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 566 567 <span class="comment">//Create a weak pointer</span> 568 <span class="identifier">weak_ptr_type</span> <span class="identifier">local_observer1</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">);</span> 569 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">());</span> 570 571 <span class="special">{</span> <span class="comment">//Create a local shared pointer from the weak pointer</span> 572 <span class="identifier">shared_ptr_type</span> <span class="identifier">local_shared_ptr</span> <span class="special">=</span> <span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">lock</span><span class="special">();</span> 573 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">owner2</span><span class="special">-></span><span class="identifier">shared_ptr_</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">());</span> 574 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span> 575 <span class="special">}</span> 576 577 <span class="comment">//Now destroy the remaining owner. "object to share" will be destroyed</span> 578 <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">owner2</span><span class="special">);</span> 579 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">type_to_share</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 580 581 <span class="comment">//Test observer</span> 582 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">expired</span><span class="special">());</span> 583 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_observer1</span><span class="special">.</span><span class="identifier">use_count</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 584 585 <span class="comment">//The reference count will be deallocated when all weak pointers</span> 586 <span class="comment">//disappear. After that, the file is unmapped.</span> 587 <span class="special">}</span> 588 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 589<span class="special">}</span> 590</pre> 591<p> 592 </p> 593<p> 594 In general, using <span class="bold"><strong>Boost.Interprocess</strong></span>' <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code> and <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> is very similar 595 to their counterparts <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a> 596 and <a href="http://www.boost.org/libs/smart_ptr/weak_ptr.htm" target="_top">boost::weak_ptr</a>, 597 but they need more template parameters and more run-time parameters in their 598 constructors. 599 </p> 600<p> 601 Just like <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a> 602 can be stored in a STL container, <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code> 603 can also be stored in <span class="bold"><strong>Boost.Interprocess</strong></span> 604 containers. 605 </p> 606<p> 607 If a programmer just uses <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">shared_ptr</a></code> 608 to be able to insert dynamically constructed objects into a container constructed 609 in the managed segment, but he does not need to share the ownership of that 610 object with other objects <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_unique_ptr.html" title="Struct template managed_unique_ptr">managed_unique_ptr</a></code> 611 is a much faster and easier to use alternative. 612 </p> 613</div> 614<div class="section"> 615<div class="titlepage"><div><div><h3 class="title"> 616<a name="interprocess.interprocess_smart_ptr.unique_ptr"></a><a class="link" href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr" title="Unique pointer">Unique 617 pointer</a> 618</h3></div></div></div> 619<p> 620 Unique ownership smart pointers are really useful to free programmers from 621 manual resource liberation of non-shared objects. <span class="bold"><strong>Boost.Interprocess</strong></span>' 622 <code class="computeroutput"><span class="identifier">unique_ptr</span></code> is much like 623 <code class="computeroutput"><a class="link" href="../boost/interprocess/scoped_ptr.html" title="Class template scoped_ptr">scoped_ptr</a></code> but 624 it's <span class="bold"><strong>moveable</strong></span> and can be easily inserted 625 in <span class="bold"><strong>Boost.Interprocess</strong></span> containers. Interprocess 626 had its own <code class="computeroutput"><span class="identifier">unique_ptr</span></code> implementation 627 but from Boost 1.57, <span class="bold"><strong>Boost.Interprocess</strong></span> 628 uses the improved and generic <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unique_ptr</span></code> 629 implementation. Here is the declaration of the unique pointer class: 630 </p> 631<pre class="programlisting"><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">D</span><span class="special">></span> 632<span class="keyword">class</span> <span class="identifier">unique_ptr</span><span class="special">;</span> 633</pre> 634<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 635<li class="listitem"> 636 T is the type of the object pointed by <code class="computeroutput"><span class="identifier">unique_ptr</span></code>. 637 </li> 638<li class="listitem"> 639 D is the deleter that will erase the object type of the object pointed 640 by the unique_ptr when the unique pointer is destroyed (and if still 641 has the ownership of the object). If the deleter defines an internal 642 <code class="computeroutput"><span class="identifier">pointer</span></code> typedef, <code class="computeroutput"><span class="identifier">unique_ptr</span></code>] will use an internal pointer 643 of the same type. So if <code class="computeroutput"><span class="identifier">D</span><span class="special">::</span><span class="identifier">pointer</span></code> 644 is <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> 645 the unique pointer will store a relative pointer instead of a raw one. 646 This allows placing <code class="computeroutput"><span class="identifier">unique_ptr</span></code> 647 in shared memory and memory-mapped files. 648 </li> 649</ul></div> 650<p> 651 <code class="computeroutput"><span class="identifier">unique_ptr</span></code> can release the 652 ownership of the stored pointer so it's useful also to be used as a rollback 653 function. One of the main properties of the class is that <span class="bold"><strong>is 654 not copyable, but only moveable</strong></span>. When a unique pointer is moved 655 to another one, the ownership of the pointer is transferred from the source 656 unique pointer to the target unique pointer. If the target unique pointer 657 owned an object, that object is first deleted before taking ownership of 658 the new object. 659 </p> 660<p> 661 <span class="bold"><strong>Boost.Interprocess</strong></span> also offers auxiliary 662 types to easily define and construct unique pointers that can be placed in 663 managed segments and will correctly delete owned object from the segment: 664 <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_unique_ptr.html" title="Struct template managed_unique_ptr">managed_unique_ptr</a></code> 665 and <code class="computeroutput"><a class="link" href="../boost/interprocess/make_managed_unique_ptr.html" title="Function template make_managed_unique_ptr">make_managed_unique_ptr</a></code> 666 utilities. 667 </p> 668<p> 669 Here we see an example of the use <code class="computeroutput"><span class="identifier">unique_ptr</span></code> 670 including creating containers of such objects: 671 </p> 672<p> 673</p> 674<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">interprocess</span><span class="special">/</span><span class="identifier">managed_mapped_file</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 675<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">smart_ptr</span><span class="special">/</span><span class="identifier">unique_ptr</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 676<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> 677<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> 678<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> 679<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 680 681<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> 682 683<span class="comment">//This is type of the object we'll allocate dynamically</span> 684<span class="keyword">struct</span> <span class="identifier">MyType</span> 685<span class="special">{</span> 686 <span class="identifier">MyType</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">number</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> 687 <span class="special">:</span> <span class="identifier">number_</span><span class="special">(</span><span class="identifier">number</span><span class="special">)</span> 688 <span class="special">{}</span> 689 <span class="keyword">int</span> <span class="identifier">number_</span><span class="special">;</span> 690<span class="special">};</span> 691 692<span class="comment">//This is the type of a unique pointer to the previous type</span> 693<span class="comment">//that will be built in the mapped file</span> 694<span class="keyword">typedef</span> <span class="identifier">managed_unique_ptr</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">unique_ptr_type</span><span class="special">;</span> 695 696<span class="comment">//Define containers of unique pointer. Unique pointer simplifies object management</span> 697<span class="keyword">typedef</span> <span class="identifier">vector</span> 698 <span class="special"><</span> <span class="identifier">unique_ptr_type</span> 699 <span class="special">,</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">unique_ptr_type</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 700 <span class="special">></span> <span class="identifier">unique_ptr_vector_t</span><span class="special">;</span> 701 702<span class="keyword">typedef</span> <span class="identifier">list</span> 703 <span class="special"><</span> <span class="identifier">unique_ptr_type</span> 704 <span class="special">,</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">unique_ptr_type</span><span class="special">,</span> <span class="identifier">managed_mapped_file</span><span class="special">::</span><span class="identifier">segment_manager</span><span class="special">></span> 705 <span class="special">></span> <span class="identifier">unique_ptr_list_t</span><span class="special">;</span> 706 707<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> 708<span class="special">{</span> 709 <span class="comment">//Define file names</span> 710 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span> <span class="special">=</span> <span class="string">"MyMappedFile"</span><span class="special">;</span> 711 712 <span class="comment">//Destroy any previous file with the name to be used.</span> 713 <span class="keyword">struct</span> <span class="identifier">file_remove</span> 714 <span class="special">{</span> 715 <span class="identifier">file_remove</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile</span><span class="special">)</span> 716 <span class="special">:</span> <span class="identifier">MappedFile_</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span> 717 <span class="special">~</span><span class="identifier">file_remove</span><span class="special">(){</span> <span class="identifier">file_mapping</span><span class="special">::</span><span class="identifier">remove</span><span class="special">(</span><span class="identifier">MappedFile_</span><span class="special">);</span> <span class="special">}</span> 718 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">MappedFile_</span><span class="special">;</span> 719 <span class="special">}</span> <span class="identifier">remover</span><span class="special">(</span><span class="identifier">MappedFile</span><span class="special">);</span> 720 <span class="special">{</span> 721 <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">create_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> 722 723 <span class="comment">//Construct an object in the file and</span> 724 <span class="comment">//pass ownership to this local unique pointer</span> 725 <span class="identifier">unique_ptr_type</span> <span class="identifier">local_unique_ptr</span> <span class="special">(</span><span class="identifier">make_managed_unique_ptr</span> 726 <span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"unique object"</span><span class="special">)(),</span> <span class="identifier">file</span><span class="special">));</span> 727 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">local_unique_ptr</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 728 729 <span class="comment">//Reset the unique pointer. The object is automatically destroyed</span> 730 <span class="identifier">local_unique_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> 731 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"unique object"</span><span class="special">).</span><span class="identifier">first</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 732 733 <span class="comment">//Now create a vector of unique pointers</span> 734 <span class="identifier">unique_ptr_vector_t</span> <span class="special">*</span><span class="identifier">unique_vector</span> <span class="special">=</span> 735 <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">unique_ptr_vector_t</span><span class="special">>(</span><span class="string">"unique vector"</span><span class="special">)(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 736 737 <span class="comment">//Speed optimization</span> 738 <span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">reserve</span><span class="special">(</span><span class="number">100</span><span class="special">);</span> 739 740 <span class="comment">//Now insert all values</span> 741 <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> 742 <span class="identifier">unique_ptr_type</span> <span class="identifier">p</span><span class="special">(</span><span class="identifier">make_managed_unique_ptr</span><span class="special">(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="identifier">anonymous_instance</span><span class="special">)(</span><span class="identifier">i</span><span class="special">),</span> <span class="identifier">file</span><span class="special">));</span> 743 <span class="identifier">unique_vector</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">p</span><span class="special">));</span> 744 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">back</span><span class="special">()-></span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span> 745 <span class="special">}</span> 746 747 <span class="comment">//Now create a list of unique pointers</span> 748 <span class="identifier">unique_ptr_list_t</span> <span class="special">*</span><span class="identifier">unique_list</span> <span class="special">=</span> 749 <span class="identifier">file</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">unique_ptr_list_t</span><span class="special">>(</span><span class="string">"unique list"</span><span class="special">)(</span><span class="identifier">file</span><span class="special">.</span><span class="identifier">get_segment_manager</span><span class="special">());</span> 750 751 <span class="comment">//Pass ownership of all values to the list</span> 752 <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">99</span><span class="special">;</span> <span class="special">!</span><span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">empty</span><span class="special">();</span> <span class="special">--</span><span class="identifier">i</span><span class="special">){</span> 753 <span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">push_front</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">unique_vector</span><span class="special">-></span><span class="identifier">back</span><span class="special">()));</span> 754 <span class="comment">//The unique ptr of the vector is now empty...</span> 755 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">back</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> 756 <span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">pop_back</span><span class="special">();</span> 757 <span class="comment">//...and the list has taken ownership of the value</span> 758 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">front</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span> 759 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">front</span><span class="special">()-></span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span> 760 <span class="special">}</span> 761 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">100</span><span class="special">);</span> 762 763 <span class="comment">//Now destroy the empty vector.</span> 764 <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_vector</span><span class="special">);</span> 765 <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk</span> 766 <span class="special">}</span> 767 <span class="special">{</span> 768 <span class="comment">//Reopen the mapped file and find again the list</span> 769 <span class="identifier">managed_mapped_file</span> <span class="identifier">file</span><span class="special">(</span><span class="identifier">open_only</span><span class="special">,</span> <span class="identifier">MappedFile</span><span class="special">);</span> 770 771 <span class="identifier">unique_ptr_list_t</span> <span class="special">*</span><span class="identifier">unique_list</span> <span class="special">=</span> 772 <span class="identifier">file</span><span class="special">.</span><span class="identifier">find</span><span class="special"><</span><span class="identifier">unique_ptr_list_t</span><span class="special">>(</span><span class="string">"unique list"</span><span class="special">).</span><span class="identifier">first</span><span class="special">;</span> 773 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">);</span> 774 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">100</span><span class="special">);</span> 775 776 <span class="identifier">unique_ptr_list_t</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">list_it</span> <span class="special">=</span> <span class="identifier">unique_list</span><span class="special">-></span><span class="identifier">begin</span><span class="special">();</span> 777 <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> <span class="special">++</span><span class="identifier">list_it</span><span class="special">){</span> 778 <span class="identifier">assert</span><span class="special">((*</span><span class="identifier">list_it</span><span class="special">)-></span><span class="identifier">number_</span> <span class="special">==</span> <span class="identifier">i</span><span class="special">);</span> 779 <span class="special">}</span> 780 781 <span class="comment">//Now destroy the list. All elements will be automatically deallocated.</span> 782 <span class="identifier">file</span><span class="special">.</span><span class="identifier">destroy_ptr</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">);</span> 783 <span class="special">}</span> 784 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 785<span class="special">}</span> 786</pre> 787<p> 788 </p> 789</div> 790</div> 791<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 792<td align="left"></td> 793<td align="right"><div class="copyright-footer">Copyright © 2005-2015 Ion Gaztanaga<p> 794 Distributed under the Boost Software License, Version 1.0. (See accompanying 795 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>) 796 </p> 797</div></td> 798</tr></table> 799<hr> 800<div class="spirit-nav"> 801<a accesskey="p" href="streams.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="architecture.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 802</div> 803</body> 804</html> 805
