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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="interprocess.interprocess_smart_ptr"></a><a class="link" href="interprocess_smart_ptr.html" title="Ownership smart pointers">Ownership smart pointers</a> |
| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.intrusive_ptr">Intrusive pointer</a></span></dt> |
| <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.scoped_ptr">Scoped pointer</a></span></dt> |
| <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.shared_ptr">Shared pointer and weak pointer</a></span></dt> |
| <dt><span class="section"><a href="interprocess_smart_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr">Unique pointer</a></span></dt> |
| </dl></div> |
| <p> |
| C++ users know the importance of ownership smart pointers when dealing with 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>, |
| <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><></span></code>... |
| </p> |
| <p> |
| When building complex shared memory/memory mapped files structures, programmers |
| would like to use also the advantages of these smart pointers. The problem is that |
| Boost and C++ TR1 smart pointers are not ready to be used for shared memory. The cause |
| is that those smart pointers contain raw pointers and they use virtual functions, |
| something that is not possible if you want to place your data in shared memory. |
| The virtual function limitation makes even impossible to achieve the same level of |
| functionality of Boost and TR1 with <span class="bold"><strong>Boost.Interprocess</strong></span> smart pointers. |
| </p> |
| <p> |
| Interprocess ownership smart pointers are mainly "smart pointers containing smart pointers", |
| so we can specify the pointer type they contain. |
| </p> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <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 pointer</a> |
| </h3></div></div></div> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/intrusive_ptr.html" title="Class template intrusive_ptr">boost::interprocess::intrusive_ptr</a></code> 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 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> we must specify the pointee type but we also must also specify |
| the pointer type to be stored in the intrusive_ptr: |
| </p> |
| <pre class="programlisting"><span class="comment">//!The intrusive_ptr class template stores a pointer to an object |
| </span><span class="comment">//!with an embedded reference count. intrusive_ptr is parameterized on |
| </span><span class="comment">//!T (the type of the object pointed to) and VoidPointer(a void pointer type |
| </span><span class="comment">//!that defines the type of pointer that intrusive_ptr will store). |
| </span><span class="comment">//!intrusive_ptr<T, void *> defines a class with a T* member whereas |
| </span><span class="comment">//!intrusive_ptr<T, offset_ptr<void> > defines a class with a offset_ptr<T> member. |
| </span><span class="comment">//!Relies on unqualified calls to: |
| </span><span class="comment">//! |
| </span><span class="comment">//!void intrusive_ptr_add_ref(T * p); |
| </span><span class="comment">//!void intrusive_ptr_release(T * p); |
| </span><span class="comment">//! |
| </span><span class="comment">//!with (p != 0) |
| </span><span class="comment">//! |
| </span><span class="comment">//!The object is responsible for destroying itself. |
| </span><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> |
| <span class="keyword">class</span> <span class="identifier">intrusive_ptr</span><span class="special">;</span> |
| </pre> |
| <p> |
| 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> 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>. But if we want to place the intrusive_ptr in |
| shared memory we must specify 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> <span class="special">></span></code> |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <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> |
| |
| <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> |
| |
| <span class="keyword">namespace</span> <span class="identifier">N</span> <span class="special">{</span> |
| |
| <span class="comment">//A class that has an internal reference count |
| </span><span class="keyword">class</span> <span class="identifier">reference_counted_class</span> |
| <span class="special">{</span> |
| <span class="keyword">private</span><span class="special">:</span> |
| <span class="comment">//Non-copyable |
| </span> <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> |
| <span class="comment">//Non-assignable |
| </span> <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> |
| <span class="comment">//A typedef to save typing |
| </span> <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> |
| <span class="comment">//This is the reference count |
| </span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">m_use_count</span><span class="special">;</span> |
| <span class="comment">//The segment manager allows deletion from shared memory segment |
| </span> <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> |
| |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">//Constructor |
| </span> <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> |
| <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> |
| <span class="comment">//Destructor |
| </span> <span class="special">~</span><span class="identifier">reference_counted_class</span><span class="special">(){}</span> |
| |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">//Returns the reference count |
| </span> <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> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">m_use_count</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="comment">//Adds a reference |
| </span> <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> |
| <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> |
| |
| <span class="comment">//Releases a reference |
| </span> <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> |
| <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> |
| <span class="special">};</span> |
| |
| <span class="special">}</span> <span class="comment">//namespace N { |
| </span> |
| <span class="comment">//A class that has an intrusive pointer to reference_counted_class |
| </span><span class="keyword">class</span> <span class="identifier">intrusive_ptr_owner</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="identifier">intrusive_ptr_t</span> <span class="identifier">m_intrusive_ptr</span><span class="special">;</span> |
| |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">//Takes a pointer to the reference counted class |
| </span> <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> |
| <span class="special">:</span> <span class="identifier">m_intrusive_ptr</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">){}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Remove shared memory on construction and destruction |
| </span> <span class="keyword">struct</span> <span class="identifier">shm_remove</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> |
| |
| <span class="comment">//Create shared memory |
| </span> <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> |
| |
| <span class="comment">//Create the unique reference counted object in shared memory |
| </span> <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Create an array of ten intrusive pointer owners in shared memory |
| </span> <span class="identifier">intrusive_ptr_owner</span> <span class="special">*</span><span class="identifier">intrusive_owner_array</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">intrusive_ptr_owner</span><span class="special">></span> |
| <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> |
| |
| <span class="comment">//Now test that reference count is ten |
| </span> <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> |
| <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> |
| |
| <span class="comment">//Now destroy the array of intrusive pointer owners |
| </span> <span class="comment">//This should destroy every intrusive_ptr and because of |
| </span> <span class="comment">//that reference_counted_class will be destroyed |
| </span> <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> |
| |
| <span class="comment">//Now the reference counted object should have been destroyed |
| </span> <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> |
| <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> |
| <span class="comment">//Success! |
| </span> <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <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 pointer</a> |
| </h3></div></div></div> |
| <p> |
| <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> 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 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 the pointer type stored by scoped_ptr. |
| </p> |
| <pre class="programlisting"><span class="comment">//!scoped_ptr stores a pointer to a dynamically allocated object. |
| </span><span class="comment">//!The object pointed to is guaranteed to be deleted, either on destruction |
| </span><span class="comment">//!of the scoped_ptr, or via an explicit reset. The user can avoid this |
| </span><span class="comment">//!deletion using release(). |
| </span><span class="comment">//!scoped_ptr is parameterized on T (the type of the object pointed to) and |
| </span><span class="comment">//!Deleter (the functor to be executed to delete the internal pointer). |
| </span><span class="comment">//!The internal pointer will be of the same pointer type as typename |
| </span><span class="comment">//!Deleter::pointer type (that is, if typename Deleter::pointer is |
| </span><span class="comment">//!offset_ptr<void>, the internal pointer will be offset_ptr<T>). |
| </span><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> |
| <span class="keyword">class</span> <span class="identifier">scoped_ptr</span><span class="special">;</span> |
| </pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code> comes handy to implement <span class="bold"><strong>rollbacks</strong></span> with exceptions: if an exception |
| is thrown or we call <code class="computeroutput"><span class="keyword">return</span></code> in the scope of <code class="computeroutput"><span class="identifier">scoped_ptr</span><span class="special"><></span></code> the deleter is |
| automatically called so that <span class="bold"><strong>the deleter can be considered as a rollback</strong></span> 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 |
| the <code class="computeroutput"><span class="identifier">scoped_ptr</span></code> goes out of scope. |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <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> |
| |
| <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> |
| |
| <span class="keyword">class</span> <span class="identifier">my_class</span> |
| <span class="special">{};</span> |
| |
| <span class="keyword">class</span> <span class="identifier">my_exception</span> |
| <span class="special">{};</span> |
| |
| <span class="comment">//A functor that destroys the shared memory object |
| </span><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">my_deleter</span> |
| <span class="special">{</span> |
| <span class="keyword">private</span><span class="special">:</span> |
| <span class="comment">//A typedef to save typing |
| </span> <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> |
| <span class="comment">//This my_deleter is created in the stack, not in shared memory, |
| </span> <span class="comment">//so we can use raw pointers |
| </span> <span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">mp_segment_manager</span><span class="special">;</span> |
| |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">//This typedef will specify the pointer type that |
| </span> <span class="comment">//scoped_ptr will store |
| </span> <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">*</span><span class="identifier">pointer</span><span class="special">;</span> |
| <span class="comment">//Constructor |
| </span> <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> |
| <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> |
| |
| <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> |
| <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> |
| <span class="special">};</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Create shared memory |
| </span> <span class="comment">//Remove shared memory on construction and destruction |
| </span> <span class="keyword">struct</span> <span class="identifier">shm_remove</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> |
| |
| <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> |
| |
| <span class="comment">//In the first try, there will be no exceptions |
| </span> <span class="comment">//in the second try we will throw an exception |
| </span> <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> |
| <span class="comment">//Create an object in shared memory |
| </span> <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Since the next shared memory allocation can throw |
| </span> <span class="comment">//assign it to a scoped_ptr so that if an exception occurs |
| </span> <span class="comment">//we destroy the object automatically |
| </span> <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> |
| |
| <span class="keyword">try</span><span class="special">{</span> |
| <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> |
| <span class="comment">//Let's emulate a exception capable operation |
| </span> <span class="comment">//In the second try, throw an exception |
| </span> <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> |
| <span class="keyword">throw</span><span class="special">(</span><span class="identifier">my_exception</span><span class="special">());</span> |
| <span class="special">}</span> |
| <span class="comment">//If we have passed the dangerous zone |
| </span> <span class="comment">//we can release the scoped pointer |
| </span> <span class="comment">//to avoid destruction |
| </span> <span class="identifier">s_ptr</span><span class="special">.</span><span class="identifier">release</span><span class="special">();</span> |
| <span class="special">}</span> |
| <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">my_exception</span> <span class="special">&){}</span> |
| <span class="comment">//Here, scoped_ptr is destroyed |
| </span> <span class="comment">//so it we haven't thrown an exception |
| </span> <span class="comment">//the object should be there, otherwise, destroyed |
| </span> <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> |
| <span class="comment">//Make sure the object is alive |
| </span> <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> |
| <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="comment">//Now we can use it and delete it manually |
| </span> <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> |
| <span class="special">}</span> |
| <span class="keyword">else</span><span class="special">{</span> |
| <span class="comment">//Make sure the object has been deleted |
| </span> <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> |
| <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <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 pointer and weak pointer</a> |
| </h3></div></div></div> |
| <p> |
| <span class="bold"><strong>Boost.Interprocess</strong></span> also offers the possibility of creating non-intrusive |
| reference-counted objects in managed shared memory or mapped files. |
| </p> |
| <p> |
| Unlike |
| <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a>, |
| 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> |
| cannot take advantage of virtual functions to maintain the same shared pointer |
| type while providing user-defined allocators and deleters. The allocator |
| and the deleter are template parameters of the shared pointer. |
| </p> |
| <p> |
| 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> must be created also in |
| the managed segment, and the deleter has to delete the object from |
| the segment, the user must specify an allocator object and 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>, just like |
| <span class="bold"><strong>Boost.Interprocess</strong></span> containers need to pass allocators in their constructors. |
| </p> |
| <p> |
| 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>: |
| </p> |
| <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> |
| <span class="keyword">class</span> <span class="identifier">shared_ptr</span><span class="special">;</span> |
| </pre> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| T is the type of the pointed type. |
| |
| </li> |
| <li class="listitem"> |
| VoidAllocator is the allocator to be used to allocate auxiliary |
| elements such as the reference count, the deleter... |
| The internal <code class="computeroutput"><span class="identifier">pointer</span></code> typedef of the allocator will determine |
| the type of pointer that shared_ptr will internally use, so |
| allocators defining <code class="computeroutput"><span class="identifier">pointer</span></code> as <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> will |
| make all internal pointers used by <code class="computeroutput"><span class="identifier">shared_ptr</span></code> 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> |
| for a working allocator. |
| |
| </li> |
| <li class="listitem"> |
| Deleter is the function object that will be used to destroy |
| the pointed object when the last reference to the object |
| is destroyed. The deleter functor will take a pointer to T |
| of the same category as the void pointer defined by |
| <code class="computeroutput"><span class="identifier">VoidAllocator</span><span class="special">::</span><span class="identifier">pointer</span></code>. See <code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code> |
| for a generic deleter that erases a object from a managed segment. |
| |
| </li> |
| </ul></div> |
| <p> |
| With correctly specified parameters, <span class="bold"><strong>Boost.Interprocess</strong></span> users |
| can create objects in shared memory that hold shared pointers pointing |
| to other objects also in shared memory, obtaining the benefits of |
| reference counting. Let's see how to create a shared pointer in a managed shared memory: |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <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> |
| <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> |
| <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> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> |
| |
| <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> |
| |
| <span class="comment">//This is type of the object we want to share |
| </span><span class="keyword">class</span> <span class="identifier">MyType</span> |
| <span class="special">{};</span> |
| |
| <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> |
| <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> |
| <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> |
| <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> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Remove shared memory on construction and destruction |
| </span> <span class="keyword">struct</span> <span class="identifier">shm_remove</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> |
| |
| <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> |
| |
| <span class="comment">//Create a shared pointer in shared memory |
| </span> <span class="comment">//pointing to a newly created object in the segment |
| </span> <span class="identifier">my_shared_ptr</span> <span class="special">&</span><span class="identifier">shared_ptr_instance</span> <span class="special">=</span> |
| <span class="special">*</span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">my_shared_ptr</span><span class="special">>(</span><span class="string">"shared ptr"</span><span class="special">)</span> |
| <span class="comment">//Arguments to construct the shared pointer |
| </span> <span class="special">(</span> <span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyType</span><span class="special">>(</span><span class="string">"object to share"</span><span class="special">)()</span> <span class="comment">//object to own |
| </span> <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> <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> <span class="special">);</span> |
| <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> |
| |
| <span class="comment">//Destroy "shared ptr". "object to share" will be automatically destroyed |
| </span> <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> |
| |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/shared_ptr.html" title="Class template shared_ptr">boost::interprocess::shared_ptr</a></code> is very flexible and |
| configurable (we can specify the allocator and the deleter, for example), |
| but as shown the creation of a shared pointer in managed segments |
| need too much typing. |
| </p> |
| <p> |
| 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> 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>) and a function |
| (<code class="computeroutput"><a class="link" href="../boost/interprocess/make_managed_shared_ptr.html" title="Function template make_managed_shared_ptr">make_managed_shared_ptr</a></code>) |
| to easily construct a shared pointer from a type allocated in a managed segment |
| with an allocator that will allocate the reference count also in the managed |
| segment and a deleter that will erase the object from the segment. |
| </p> |
| <p> |
| These utilities will use a <span class="bold"><strong>Boost.Interprocess</strong></span> allocator |
| (<code class="computeroutput"><a class="link" href="../boost/interprocess/allocator.html" title="Class template allocator">boost::interprocess::allocator</a></code>) |
| and deleter (<code class="computeroutput"><a class="link" href="../boost/interprocess/deleter.html" title="Class template deleter">boost::interprocess::deleter</a></code>) to do their job. |
| The definition of the previous shared pointer |
| could be simplified to the following: |
| </p> |
| <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> |
| </pre> |
| <p> |
| And the creation of a shared pointer can be simplified to this: |
| </p> |
| <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> |
| <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> |
| </pre> |
| <p> |
| <span class="bold"><strong>Boost.Interprocess</strong></span> also offers a weak pointer named |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> (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> 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> 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>. |
| </p> |
| <p> |
| 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>: |
| and |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/weak_ptr.html" title="Class template weak_ptr">weak_ptr</a></code> |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <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> |
| <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> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> |
| |
| <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> |
| |
| <span class="comment">//This is type of the object we want to share |
| </span><span class="keyword">struct</span> <span class="identifier">type_to_share</span> |
| <span class="special">{};</span> |
| |
| <span class="comment">//This is the type of a shared pointer to the previous type |
| </span><span class="comment">//that will be built in the mapped file |
| </span><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> |
| <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> |
| |
| <span class="comment">//This is a type holding a shared pointer |
| </span><span class="keyword">struct</span> <span class="identifier">shared_ptr_owner</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="special">{}</span> |
| |
| <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> |
| <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> |
| <span class="special">{}</span> |
| |
| <span class="identifier">shared_ptr_type</span> <span class="identifier">shared_ptr_</span><span class="special">;</span> |
| <span class="comment">//... |
| </span><span class="special">};</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Destroy any previous file with the name to be used. |
| </span> <span class="keyword">struct</span> <span class="identifier">file_remove</span> |
| <span class="special">{</span> |
| <span class="identifier">file_remove</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="string">"MyMappedFile"</span><span class="special">);</span> <span class="special">}</span> |
| <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="string">"MyMappedFile"</span><span class="special">);</span> <span class="special">}</span> |
| <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> |
| <span class="special">{</span> |
| <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="string">"MyMappedFile"</span><span class="special">,</span> <span class="number">4096</span><span class="special">);</span> |
| |
| <span class="comment">//Construct the shared type in the file and |
| </span> <span class="comment">//pass ownership to this local shared pointer |
| </span> <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Share ownership of the object between local_shared_ptr and a new "owner1" |
| </span> <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">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> |
| <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> |
| |
| <span class="comment">//local_shared_ptr releases object ownership |
| </span> <span class="identifier">local_shared_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> |
| <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> |
| <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> |
| |
| <span class="comment">//Share ownership of the object between "owner1" and a new "owner2" |
| </span> <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">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> |
| <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> |
| <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> |
| <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> |
| |
| <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk |
| </span> <span class="special">}</span> |
| <span class="special">{</span> |
| <span class="comment">//Reopen the mapped file and find again all owners |
| </span> <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="string">"MyMappedFile"</span><span class="special">);</span> |
| |
| <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Check everything is as expected |
| </span> <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> |
| <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Now destroy one of the owners, the reference count drops. |
| </span> <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> |
| <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> |
| |
| <span class="comment">//Create a weak pointer |
| </span> <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> |
| <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> |
| |
| <span class="special">{</span> <span class="comment">//Create a local shared pointer from the weak pointer |
| </span> <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> |
| <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> |
| <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> |
| <span class="special">}</span> |
| |
| <span class="comment">//Now destroy the remaining owner. "object to share" will be destroyed |
| </span> <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> |
| <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> |
| |
| <span class="comment">//Test observer |
| </span> <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> |
| <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> |
| |
| <span class="comment">//The reference count will be deallocated when all weak pointers |
| </span> <span class="comment">//disappear. After that, the file is unmapped. |
| </span> <span class="special">}</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| 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 to their |
| counterparts <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a> |
| and <a href="http://www.boost.org/libs/smart_ptr/weak_ptr.htm" target="_top">boost::weak_ptr</a>, but |
| they need more template parameters and more run-time parameters in their constructors. |
| </p> |
| <p> |
| Just like <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">boost::shared_ptr</a> |
| 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> |
| can also be stored in <span class="bold"><strong>Boost.Interprocess</strong></span> containers. |
| </p> |
| <p> |
| 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> |
| to be able to insert objects dynamically constructed in the managed segment |
| in a container, but does not need to share the ownership of that object with |
| other objects <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> is a much |
| faster and easier to use alternative. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <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 pointer</a> |
| </h3></div></div></div> |
| <p> |
| Unique ownership smart pointers are really useful to free programmers from |
| manual resource liberation of non-shared objects. <span class="bold"><strong>Boost.Interprocess</strong></span>' |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> is much like |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/scoped_ptr.html" title="Class template scoped_ptr">scoped_ptr</a></code> but it's <span class="bold"><strong>moveable</strong></span> |
| and can be easily inserted in <span class="bold"><strong>Boost.Interprocess</strong></span> containers. |
| Here is the declaration of the unique pointer class: |
| </p> |
| <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> |
| <span class="keyword">class</span> <span class="identifier">unique_ptr</span><span class="special">;</span> |
| </pre> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| T is the type of the object pointed by <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code>. |
| |
| </li> |
| <li class="listitem"> |
| D is the deleter that will erase the object type of the object pointed by |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> when the unique pointer |
| is destroyed (and if still owns ownership of the object). If the deleter defines |
| an internal <code class="computeroutput"><span class="identifier">pointer</span></code> typedef, <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> |
| will use an internal pointer of the same type. So if <code class="computeroutput"><span class="identifier">D</span><span class="special">::</span><span class="identifier">pointer</span></code> is <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| the unique pointer will store a relative pointer instead of a raw one. This |
| allows placing <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> in shared |
| memory and memory-mapped files. |
| |
| </li> |
| </ul></div> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> can release the ownership of |
| the stored pointer so it's useful also to be used as a rollback function. One of the main |
| properties of the class is that <span class="bold"><strong>is not copyable, but only moveable</strong></span>. When a unique |
| pointer is moved to another one, the ownership of the pointer is transferred from |
| the source unique pointer to the target unique pointer. If the target unique pointer |
| owned an object, that object is first deleted before taking ownership of the new object. |
| </p> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> also offers auxiliary types to |
| easily define and construct unique pointers that can be placed in managed segments |
| and will correctly delete the owned object from the segment: |
| <code class="computeroutput"><a class="link" href="../boost/interprocess/managed_unique_ptr.html" title="Struct template managed_unique_ptr">managed_unique_ptr</a></code> |
| 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> |
| utilities. |
| </p> |
| <p> |
| Here we see an example of the use <code class="computeroutput"><a class="link" href="../boost/interprocess/unique_ptr.html" title="Class template unique_ptr">unique_ptr</a></code> |
| including creating containers of such objects: |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <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> |
| <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> |
| <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> |
| <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> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> |
| |
| <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> |
| |
| <span class="comment">//This is type of the object we'll allocate dynamically |
| </span><span class="keyword">struct</span> <span class="identifier">MyType</span> |
| <span class="special">{</span> |
| <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> |
| <span class="special">:</span> <span class="identifier">number_</span><span class="special">(</span><span class="identifier">number</span><span class="special">)</span> |
| <span class="special">{}</span> |
| <span class="keyword">int</span> <span class="identifier">number_</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="comment">//This is the type of a unique pointer to the previous type |
| </span><span class="comment">//that will be built in the mapped file |
| </span><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> |
| |
| <span class="comment">//Define containers of unique pointer. Unique pointer simplifies object management |
| </span><span class="keyword">typedef</span> <span class="identifier">vector</span> |
| <span class="special"><</span> <span class="identifier">unique_ptr_type</span> |
| <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> |
| <span class="special">></span> <span class="identifier">unique_ptr_vector_t</span><span class="special">;</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">list</span> |
| <span class="special"><</span> <span class="identifier">unique_ptr_type</span> |
| <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> |
| <span class="special">></span> <span class="identifier">unique_ptr_list_t</span><span class="special">;</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Destroy any previous file with the name to be used. |
| </span> <span class="keyword">struct</span> <span class="identifier">file_remove</span> |
| <span class="special">{</span> |
| <span class="identifier">file_remove</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="string">"MyMappedFile"</span><span class="special">);</span> <span class="special">}</span> |
| <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="string">"MyMappedFile"</span><span class="special">);</span> <span class="special">}</span> |
| <span class="special">}</span> <span class="identifier">remover</span><span class="special">;</span> |
| <span class="special">{</span> |
| <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="string">"MyMappedFile"</span><span class="special">,</span> <span class="number">65536</span><span class="special">);</span> |
| |
| <span class="comment">//Construct an object in the file and |
| </span> <span class="comment">//pass ownership to this local unique pointer |
| </span> <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> |
| <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> |
| <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> |
| |
| <span class="comment">//Reset the unique pointer. The object is automatically destroyed |
| </span> <span class="identifier">local_unique_ptr</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> |
| <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> |
| |
| <span class="comment">//Now create a vector of unique pointers |
| </span> <span class="identifier">unique_ptr_vector_t</span> <span class="special">*</span><span class="identifier">unique_vector</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">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> |
| |
| <span class="comment">//Speed optimization |
| </span> <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> |
| |
| <span class="comment">//Now insert all values |
| </span> <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="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> |
| <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">interprocess</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">p</span><span class="special">));</span> |
| <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> |
| <span class="special">}</span> |
| |
| <span class="comment">//Now create a list of unique pointers |
| </span> <span class="identifier">unique_ptr_list_t</span> <span class="special">*</span><span class="identifier">unique_list</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">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> |
| |
| <span class="comment">//Pass ownership of all values to the list |
| </span> <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> |
| <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">interprocess</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> |
| <span class="comment">//The unique ptr of the vector is now empty... |
| </span> <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> |
| <span class="identifier">unique_vector</span><span class="special">-></span><span class="identifier">pop_back</span><span class="special">();</span> |
| <span class="comment">//...and the list has taken ownership of the value |
| </span> <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> |
| <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> |
| <span class="special">}</span> |
| <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> |
| |
| <span class="comment">//Now destroy the empty vector. |
| </span> <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> |
| <span class="comment">//The mapped file is unmapped here. Objects have been flushed to disk |
| </span> <span class="special">}</span> |
| <span class="special">{</span> |
| <span class="comment">//Reopen the mapped file and find again the list |
| </span> <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="string">"MyMappedFile"</span><span class="special">);</span> |
| |
| <span class="identifier">unique_ptr_list_t</span> <span class="special">*</span><span class="identifier">unique_list</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">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> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">unique_list</span><span class="special">);</span> |
| <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> |
| |
| <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> |
| <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> |
| <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> |
| <span class="special">}</span> |
| |
| <span class="comment">//Now destroy the list. All elements will be automatically deallocated. |
| </span> <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> |
| <span class="special">}</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2005 - 2010 Ion Gaztanaga<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
| </div></td> |
| </tr></table> |
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