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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="interprocess.customizing_interprocess"></a><a class="link" href="customizing_interprocess.html" title="Customizing Boost.Interprocess">Customizing Boost.Interprocess</a> |
| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_interprocess_alloc">Writing a new shared memory allocation algorithm</a></span></dt> |
| <dt><span class="section"><a href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_allocators">Building custom STL compatible allocators for Boost.Interprocess</a></span></dt> |
| <dt><span class="section"><a href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_indexes">Building custom indexes</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="interprocess.customizing_interprocess.custom_interprocess_alloc"></a><a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_interprocess_alloc" title="Writing a new shared memory allocation algorithm">Writing a new shared memory allocation algorithm</a> |
| </h3></div></div></div> |
| <p> |
| If the default algorithm does not satisfy user requirements, |
| it's easy to provide different algorithms like bitmapping or |
| more advanced segregated lists to meet requirements. The class implementing |
| the algorithm must be compatible with shared memory, so it shouldn't have any |
| virtual function or virtual inheritance or |
| any indirect base class with virtual function or inheritance. |
| </p> |
| <p> |
| This is the interface to be implemented: |
| </p> |
| <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">my_algorithm</span> |
| <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| |
| <span class="comment">//!The mutex type to be used by the rest of Interprocess framework |
| </span> <span class="keyword">typedef</span> <span class="identifier">implementation_defined</span> <span class="identifier">mutex_family</span><span class="special">;</span> |
| |
| <span class="comment">//!The pointer type to be used by the rest of Interprocess framework |
| </span> <span class="keyword">typedef</span> <span class="identifier">implementation_defined</span> <span class="identifier">void_pointer</span><span class="special">;</span> |
| |
| <span class="comment">//!Constructor. "size" is the total size of the managed memory segment, |
| </span> <span class="comment">//!"extra_hdr_bytes" indicates the extra bytes after the sizeof(my_algorithm) |
| </span> <span class="comment">//!that the allocator should not use at all. |
| </span> <span class="identifier">my_algorithm</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">extra_hdr_bytes</span><span class="special">);</span> |
| |
| <span class="comment">//!Obtains the minimum size needed by the algorithm |
| </span> <span class="keyword">static</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_min_size</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">extra_hdr_bytes</span><span class="special">);</span> |
| |
| <span class="comment">//!Allocates bytes, returns 0 if there is not more memory |
| </span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">allocate</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">nbytes</span><span class="special">);</span> |
| |
| <span class="comment">//!Deallocates previously allocated bytes |
| </span> <span class="keyword">void</span> <span class="identifier">deallocate</span> <span class="special">(</span><span class="keyword">void</span> <span class="special">*</span><span class="identifier">adr</span><span class="special">);</span> |
| |
| <span class="comment">//!Returns the size of the memory segment |
| </span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">get_size</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> |
| |
| <span class="comment">//!Increases managed memory in extra_size bytes more |
| </span> <span class="keyword">void</span> <span class="identifier">grow</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">extra_size</span><span class="special">);</span> |
| <span class="comment">/*...*/</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Let's see the public typedefs to define: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="comment">/* . . . */</span> <span class="identifier">void_pointer</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/* . . . */</span> <span class="identifier">mutex_family</span><span class="special">;</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">void_pointer</span></code> typedef specifies the pointer type to be used in |
| the <span class="bold"><strong>Boost.Interprocess</strong></span> framework that uses the algorithm. For example, if we define |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="keyword">void</span> <span class="special">*</span> <span class="identifier">void_pointer</span><span class="special">;</span> |
| </pre> |
| <p> |
| all <span class="bold"><strong>Boost.Interprocess</strong></span> framework using this algorithm will use raw pointers as members. |
| But if we define: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="identifier">void_pointer</span><span class="special">;</span> |
| </pre> |
| <p> |
| then all <span class="bold"><strong>Boost.Interprocess</strong></span> framework will use relative pointers. |
| </p> |
| <p> |
| The <code class="computeroutput"><span class="identifier">mutex_family</span></code> is a structure containing typedefs |
| for different interprocess_mutex types to be used in the <span class="bold"><strong>Boost.Interprocess</strong></span> |
| framework. For example the defined |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">mutex_family</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">interprocess_mutex</span> <span class="identifier">mutex_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">interprocess_recursive_mutex</span> <span class="identifier">recursive_mutex_type</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| defines all interprocess_mutex types using boost::interprocess interprocess_mutex types. |
| The user can specify the desired mutex family. |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">mutex_family</span> <span class="identifier">mutex_family</span><span class="special">;</span> |
| </pre> |
| <p> |
| The new algorithm (let's call it <span class="bold"><strong>my_algorithm</strong></span>) must implement all the functions |
| that boost::interprocess::rbtree_best_fit class offers: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <p class="simpara"> |
| <span class="bold"><strong>my_algorithm</strong></span>'s constructor must take 2 arguments: |
| |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="circle"> |
| <li class="listitem"> |
| <span class="bold"><strong>size</strong></span> indicates the total size of the managed memory segment, and |
| <span class="bold"><strong>my_algorithm</strong></span> object will be always constructed a at offset 0 |
| of the memory segment. |
| |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>extra_hdr_bytes</strong></span> parameter indicates the number of bytes after |
| the offset <code class="computeroutput"><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">my_algorithm</span><span class="special">)</span></code> that <span class="bold"><strong>my_algorithm</strong></span> can't use at all. This extra |
| bytes will be used to store additional data that should not be overwritten. |
| So, <span class="bold"><strong>my_algorithm</strong></span> will be placed at address XXX of the memory segment, and will |
| manage the <span class="bold"><strong>[XXX + sizeof(my_algorithm) + extra_hdr_bytes, XXX + size)</strong></span> range of |
| the segment. |
| |
| </li> |
| </ul></div> |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>get_min_size()</strong></span> function should return the minimum space the algorithm |
| needs to be valid with the passed <span class="bold"><strong>extra_hdr_bytes</strong></span> parameter. This function will |
| be used to check if the memory segment is big enough to place the algorithm there. |
| |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>allocate()</strong></span> function must return 0 if there is no more available memory. |
| The memory returned by <span class="bold"><strong>my_algorithm</strong></span> |
| must be aligned to the most restrictive memory alignment of the system, for example, |
| to the value returned by <span class="bold"><strong>detail::alignment_of<boost::detail::max_align>::value</strong></span>. |
| This function should be executed with the synchronization capabilities offered |
| by <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">mutex_family</span><span class="special">::</span><span class="identifier">mutex_type</span></code> interprocess_mutex. That means, that if we define |
| <code class="computeroutput"><span class="keyword">typedef</span> <span class="identifier">mutex_family</span> <span class="identifier">mutex_family</span><span class="special">;</span></code> then this function should offer |
| the same synchronization as if it was surrounded by an interprocess_mutex lock/unlock. |
| Normally, this is implemented using a member of type <code class="computeroutput"><span class="identifier">mutex_family</span><span class="special">::</span><span class="identifier">mutex_type</span></code>, but |
| it could be done using atomic instructions or lock free algorithms. |
| |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>deallocate()</strong></span> function must make the returned buffer available for new |
| allocations. This function should offer the same synchronization as <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>. |
| |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>size()</strong></span> function will return the passed <span class="bold"><strong>size</strong></span> parameter in the constructor. |
| So, <span class="bold"><strong>my_algorithm</strong></span> should store the size internally. |
| |
| </li> |
| <li class="listitem"> |
| The <span class="bold"><strong>grow()</strong></span> function will expand the managed memory by <span class="bold"><strong>my_algorithm</strong></span> in <span class="bold"><strong>extra_size</strong></span> |
| bytes. So <span class="bold"><strong>size()</strong></span> function should return the updated size, |
| and the new managed memory range will be (if the address where the algorithm is |
| constructed is XXX): <span class="bold"><strong>[XXX + sizeof(my_algorithm) + extra_hdr_bytes, XXX + old_size + extra_size)</strong></span>. |
| This function should offer the same synchronization as <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>. |
| |
| </li> |
| </ul></div> |
| <p> |
| That's it. Now we can create new managed shared memory that uses our new algorithm: |
| </p> |
| <pre class="programlisting"><span class="comment">//Managed memory segment to allocate named (c-string) objects |
| </span><span class="comment">//using a user-defined memory allocation algorithm |
| </span><span class="identifier">basic_managed_shared_memory</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> |
| <span class="special">,</span><span class="identifier">my_algorithm</span> |
| <span class="special">,</span><span class="identifier">flat_map_index</span><span class="special">></span> |
| <span class="identifier">my_managed_shared_memory</span><span class="special">;</span> |
| </pre> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="interprocess.customizing_interprocess.custom_allocators"></a><a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_allocators" title="Building custom STL compatible allocators for Boost.Interprocess">Building custom STL compatible allocators for Boost.Interprocess</a> |
| </h3></div></div></div> |
| <p> |
| If provided STL-like allocators don't satisfy user needs, the user |
| can implement another STL compatible allocator using raw memory allocation |
| and named object construction functions. |
| The user can this way implement more suitable allocation |
| schemes on top of basic shared memory allocation schemes, |
| just like more complex allocators are built on top of |
| new/delete functions. |
| </p> |
| <p> |
| When using a managed memory segment, <span class="bold"><strong>get_segment_manager()</strong></span> |
| function returns a pointer to the segment manager. With this pointer, |
| the raw memory allocation and named object construction functions can be |
| called directly: |
| </p> |
| <pre class="programlisting"><span class="comment">//Create the managed shared memory and initialize resources |
| </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="comment">//segment name |
| </span> <span class="special">,</span><span class="number">65536</span><span class="special">);</span> <span class="comment">//segment size in bytes |
| </span> |
| <span class="comment">//Obtain the segment manager |
| </span><span class="identifier">managed_shared_memory</span><span class="special">::</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">segment_mngr</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">//With the segment manager, now we have access to all allocation functions |
| </span><span class="identifier">segment_mngr</span><span class="special">-></span><span class="identifier">deallocate</span><span class="special">(</span><span class="identifier">segment_mngr</span><span class="special">-></span><span class="identifier">allocate</span><span class="special">(</span><span class="number">32</span><span class="special">));</span> |
| <span class="identifier">segment_mngr</span><span class="special">-></span><span class="identifier">construct</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"My_Int"</span><span class="special">)[</span><span class="number">32</span><span class="special">](</span><span class="number">0</span><span class="special">);</span> |
| <span class="identifier">segment_mngr</span><span class="special">-></span><span class="identifier">destroy</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="string">"My_Int"</span><span class="special">);</span> |
| |
| <span class="comment">//Initialize the custom, managed memory segment compatible |
| </span><span class="comment">//allocator with the segment manager. |
| </span><span class="comment">// |
| </span><span class="comment">//MySTLAllocator uses segment_mngr->xxx functions to |
| </span><span class="comment">//implement its allocation scheme |
| </span><span class="identifier">MySTLAllocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">stl_alloc</span><span class="special">(</span><span class="identifier">segment_mngr</span><span class="special">);</span> |
| |
| <span class="comment">//Alias a new vector type that uses the custom STL compatible allocator |
| </span><span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">MySTLAllocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">MyVect</span><span class="special">;</span> |
| |
| <span class="comment">//Construct the vector in shared memory with the allocator as constructor parameter |
| </span><span class="identifier">segment</span><span class="special">.</span><span class="identifier">construct</span><span class="special"><</span><span class="identifier">MyVect</span><span class="special">>(</span><span class="string">"MyVect_instance"</span><span class="special">)(</span><span class="identifier">stl_alloc</span><span class="special">);</span> |
| </pre> |
| <p> |
| The user can create new STL compatible allocators that use the segment manager to access |
| to all memory management/object construction functions. All <span class="bold"><strong>Boost.Interprocess</strong></span>' STL |
| compatible allocators are based on this approach. <span class="bold"><strong>Remember</strong></span> that to be compatible with |
| managed memory segments, allocators should define their <span class="bold"><strong>pointer</strong></span> typedef as the same |
| pointer family as <code class="computeroutput"><span class="identifier">segment_manager</span><span class="special">::</span><span class="identifier">void_pointer</span></code> typedef. This means that if <code class="computeroutput"><span class="identifier">segment_manager</span><span class="special">::</span><span class="identifier">void_pointer</span></code> is |
| <code class="computeroutput"><span class="identifier">offset_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code>, <code class="computeroutput"><span class="identifier">MySTLAllocator</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> should define <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">int</span><span class="special">></span></code>. The |
| reason for this is that allocators are members of containers, and if we want to put |
| the container in a managed memory segment, the allocator should be ready for that. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="interprocess.customizing_interprocess.custom_indexes"></a><a class="link" href="customizing_interprocess.html#interprocess.customizing_interprocess.custom_indexes" title="Building custom indexes">Building custom indexes</a> |
| </h3></div></div></div> |
| <p> |
| The managed memory segment uses a name/object index to |
| speed up object searching and creation. Default specializations of |
| managed memory segments (<code class="computeroutput"><span class="identifier">managed_shared_memory</span></code> for example), |
| use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">flat_map</span></code> as index. |
| </p> |
| <p> |
| However, the index type can be chosen via template parameter, so that |
| the user can define its own index type if he needs that. To construct |
| a new index type, the user must create a class with the following guidelines: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| The interface of the index must follow the common public interface of std::map |
| and std::tr1::unordered_map including public typedefs. |
| The <code class="computeroutput"><span class="identifier">value_type</span></code> typedef can be of type: |
| |
| </li></ul></div> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">key_type</span><span class="special">,</span> <span class="identifier">mapped_type</span><span class="special">></span> |
| </pre> |
| <p> |
| or |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">key_type</span><span class="special">,</span> <span class="identifier">mapped_type</span><span class="special">></span> |
| </pre> |
| <p> |
| so that ordered arrays or deques can be used as index types. |
| Some known classes following this basic interface are <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unordered_map</span></code>, |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">flat_map</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">map</span></code>. |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| The class must be a class template taking only a traits struct of this type: |
| |
| </li></ul></div> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">index_traits</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="comment">/*...*/</span> <span class="identifier">key_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*...*/</span> <span class="identifier">mapped_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*...*/</span> <span class="identifier">segment_manager</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">IndexTraits</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">my_index_type</span><span class="special">;</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">key_type</span></code> typedef of the passed <code class="computeroutput"><span class="identifier">index_traits</span></code> will be a specialization of the |
| following class: |
| </p> |
| <pre class="programlisting"><span class="comment">//!The key of the named allocation information index. Stores a to |
| </span><span class="comment">//!a null string and the length of the string to speed up sorting |
| </span><span class="keyword">template</span><span class="special"><...></span> |
| <span class="keyword">struct</span> <span class="identifier">index_key</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="comment">/*...*/</span> <span class="identifier">char_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*...*/</span> <span class="identifier">const_char_ptr_t</span><span class="special">;</span> |
| |
| <span class="comment">//Pointer to the object's name (null terminated) |
| </span> <span class="identifier">const_char_ptr_t</span> <span class="identifier">mp_str</span><span class="special">;</span> |
| |
| <span class="comment">//Length of the name buffer (null NOT included) |
| </span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">m_len</span><span class="special">;</span> |
| |
| <span class="comment">//!Constructor of the key |
| </span> <span class="identifier">index_key</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">CharT</span> <span class="special">*</span><span class="identifier">name</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">length</span><span class="special">);</span> |
| |
| <span class="comment">//!Less than function for index ordering |
| </span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special"><</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">index_key</span> <span class="special">&</span> <span class="identifier">right</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| |
| <span class="comment">//!Equal to function for index ordering |
| </span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">index_key</span> <span class="special">&</span> <span class="identifier">right</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">mapped_type</span></code> is not directly modified by the customized index but it is needed to |
| define the index type. The <span class="bold"><strong>segment_manager</strong></span> will be the type of the segment manager that |
| will manage the index. <code class="computeroutput"><span class="identifier">segment_manager</span></code> will define interesting internal types like |
| <code class="computeroutput"><span class="identifier">void_pointer</span></code> or <code class="computeroutput"><span class="identifier">mutex_family</span></code>. |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| The constructor of the customized index type must take a pointer to segment_manager |
| as constructor argument: |
| |
| </li></ul></div> |
| <pre class="programlisting"><span class="identifier">constructor</span><span class="special">(</span><span class="identifier">segment_manager</span> <span class="special">*</span><span class="identifier">segment_mngr</span><span class="special">);</span> |
| </pre> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| The index must provide a memory reservation function, that optimizes the index if the |
| user knows the number of elements to be inserted in the index: |
| |
| </li></ul></div> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">reserve</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">);</span> |
| </pre> |
| <p> |
| For example, the index type <code class="computeroutput"><span class="identifier">flat_map_index</span></code> based in <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">flat_map</span></code> |
| is just defined as: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">interprocess</span> <span class="special">{</span> |
| |
| <span class="comment">//!Helper class to define typedefs from IndexTraits |
| </span><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">MapConfig</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">flat_map_index_aux</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">MapConfig</span><span class="special">::</span><span class="identifier">key_type</span> <span class="identifier">key_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">MapConfig</span><span class="special">::</span><span class="identifier">mapped_type</span> <span class="identifier">mapped_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">MapConfig</span><span class="special">::</span> |
| <span class="identifier">segment_manager_base</span> <span class="identifier">segment_manager_base</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special"><</span><span class="identifier">key_type</span><span class="special">></span> <span class="identifier">key_less</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">key_type</span><span class="special">,</span> <span class="identifier">mapped_type</span><span class="special">></span> <span class="identifier">value_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">allocator</span><span class="special"><</span><span class="identifier">value_type</span> |
| <span class="special">,</span><span class="identifier">segment_manager_base</span><span class="special">></span> <span class="identifier">allocator_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">flat_map</span><span class="special"><</span><span class="identifier">key_type</span><span class="special">,</span> <span class="identifier">mapped_type</span><span class="special">,</span> |
| <span class="identifier">key_less</span><span class="special">,</span> <span class="identifier">allocator_type</span><span class="special">></span> <span class="identifier">index_t</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="comment">//!Index type based in flat_map. Just derives from flat_map and |
| </span><span class="comment">//!defines the interface needed by managed memory segments. |
| </span><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">MapConfig</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">flat_map_index</span> |
| <span class="comment">//Derive class from flat_map specialization |
| </span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">flat_map_index_aux</span><span class="special"><</span><span class="identifier">MapConfig</span><span class="special">>::</span><span class="identifier">index_t</span> |
| <span class="special">{</span> |
| <span class="comment">/// @cond |
| </span> <span class="keyword">typedef</span> <span class="identifier">flat_map_index_aux</span><span class="special"><</span><span class="identifier">MapConfig</span><span class="special">></span> <span class="identifier">index_aux</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">index_aux</span><span class="special">::</span><span class="identifier">index_t</span> <span class="identifier">base_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">index_aux</span><span class="special">::</span> |
| <span class="identifier">segment_manager_base</span> <span class="identifier">segment_manager_base</span><span class="special">;</span> |
| <span class="comment">/// @endcond |
| </span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">//!Constructor. Takes a pointer to the segment manager. Can throw |
| </span> <span class="identifier">flat_map_index</span><span class="special">(</span><span class="identifier">segment_manager_base</span> <span class="special">*</span><span class="identifier">segment_mngr</span><span class="special">)</span> |
| <span class="special">:</span> <span class="identifier">base_type</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">index_aux</span><span class="special">::</span><span class="identifier">key_less</span><span class="special">(),</span> |
| <span class="keyword">typename</span> <span class="identifier">index_aux</span><span class="special">::</span><span class="identifier">allocator_type</span><span class="special">(</span><span class="identifier">segment_mngr</span><span class="special">))</span> |
| <span class="special">{}</span> |
| |
| <span class="comment">//!This reserves memory to optimize the insertion of n elements in the index |
| </span> <span class="keyword">void</span> <span class="identifier">reserve</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span> |
| <span class="special">{</span> <span class="identifier">base_type</span><span class="special">::</span><span class="identifier">reserve</span><span class="special">(</span><span class="identifier">n</span><span class="special">);</span> <span class="special">}</span> |
| |
| <span class="comment">//!This frees all unnecessary memory |
| </span> <span class="keyword">void</span> <span class="identifier">shrink_to_fit</span><span class="special">()</span> |
| <span class="special">{</span> <span class="identifier">base_type</span><span class="special">::</span><span class="identifier">shrink_to_fit</span><span class="special">();</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="special">}}</span> <span class="comment">//namespace boost { namespace interprocess |
| </span></pre> |
| <p> |
| </p> |
| <p> |
| If the user is defining a node container based index (a container whose iterators |
| are not invalidated when inserting or erasing other elements), <span class="bold"><strong>Boost.Interprocess</strong></span> can |
| optimize named object destruction when destructing via pointer. <span class="bold"><strong>Boost.Interprocess</strong></span> can |
| store an iterator next to the object and instead of using the name of the object to erase |
| the index entry, it uses the iterator, which is a faster operation. So if you are creating |
| a new node container based index (for example, a tree), you should define an |
| specialization of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">interprocess</span><span class="special">::</span><span class="identifier">is_node_index</span><span class="special"><...></span></code> defined in |
| <code class="computeroutput"><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">detail</span><span class="special">/</span><span class="identifier">utilities</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>: |
| </p> |
| <pre class="programlisting"><span class="comment">//!Trait classes to detect if an index is a node |
| </span><span class="comment">//!index. This allows more efficient operations |
| </span><span class="comment">//!when deallocating named objects. |
| </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">MapConfig</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">is_node_index</span> |
| <span class="special"><</span><span class="identifier">my_index</span><span class="special"><</span><span class="identifier">MapConfig</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">enum</span> <span class="special">{</span> <span class="identifier">value</span> <span class="special">=</span> <span class="keyword">true</span> <span class="special">};</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Interprocess also defines other index types: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <span class="bold"><strong>boost::map_index</strong></span> uses <span class="bold"><strong>boost::interprocess::map</strong></span> as index type. |
| |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>boost::null_index</strong></span> that uses an dummy index type if the user just needs |
| anonymous allocations and wants to save some space and class instantations. |
| |
| </li> |
| </ul></div> |
| <p> |
| Defining a new managed memory segment that uses the new index is easy. For |
| example, a new managed shared memory that uses the new index: |
| </p> |
| <pre class="programlisting"><span class="comment">//!Defines a managed shared memory with a c-strings as |
| </span><span class="comment">//!a keys, the red-black tree best fit algorithm (with process-shared mutexes |
| </span><span class="comment">//!and offset_ptr pointers) as raw shared memory management algorithm |
| </span><span class="comment">//!and a custom index |
| </span><span class="keyword">typedef</span> |
| <span class="identifier">basic_managed_shared_memory</span> <span class="special"><</span> |
| <span class="keyword">char</span><span class="special">,</span> |
| <span class="identifier">rbtree_best_fit</span><span class="special"><</span><span class="identifier">mutex_family</span><span class="special">>,</span> |
| <span class="identifier">my_index_type</span> |
| <span class="special">></span> |
| <span class="identifier">my_managed_shared_memory</span><span class="special">;</span> |
| </pre> |
| </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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