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<img src="../../../../boost.png" width="276" height="86" alt="C++ Boost">
<h1 align="center">Singleton Pool</h1>
<h2>Introduction</h2>
<p>singleton_pool.hpp provides a template class <span class=
"code">singleton_pool</span>, which provides access to a <span class=
"code">pool</span> as a singleton object. For information on other
pool-based interfaces, see <a href="../interfaces.html">the other pool
interfaces</a>.</p>
<h2>Synopsis</h2>
<pre class="code">
template <typename Tag, unsigned RequestedSize,
typename UserAllocator = default_user_allocator_new_delete>
struct singleton_pool
{
public:
typedef Tag tag;
typedef UserAllocator user_allocator;
typedef typename pool<UserAllocator>::size_type size_type;
typedef typename pool<UserAllocator>::difference_type difference_type;
static const unsigned requested_size = RequestedSize;
private:
static pool<size_type> p; // exposition only!
singleton_pool();
public:
static bool is_from(void * ptr);
static void * malloc();
static void * ordered_malloc();
static void * ordered_malloc(size_type n);
static void free(void * ptr);
static void ordered_free(void * ptr);
static void free(void * ptr, std::size_t n);
static void ordered_free(void * ptr, size_type n);
static bool release_memory();
static bool purge_memory();
};
</pre>
<h2>Notes</h2>
<p>The underlying pool <span class="code">p</span> referenced by the static
functions in <span class="code">singleton_pool</span> is actually declared
in a way that it is:</p>
<ul>
<li>Thread-safe if there is only one thread running before main() begins
and after main() ends -- all of the static functions of <span class=
"code">singleton_pool</span> synchronize their access to <span class=
"code">p</span>.</li>
<li>Guaranteed to be constructed before it is used -- thus, the simple
static object in the synopsis above would actually be an incorrect
implementation. The actual <a href=
"../implementation/singleton_pool.html">implementation</a> to guarantee
this is considerably more complicated.</li>
</ul>
<p>Note that a different underlying pool <span class="code">p</span> exists
for each different set of template parameters, including <a href=
"../implementation/singleton_pool.html">implementation-specific
ones</a>.</p>
<h2>Template Parameters</h2>
<h3>Tag</h3>
<p>The <span class="code">Tag</span> template parameter allows different
unbounded sets of singleton pools to exist. For example, the <a href=
"pool_alloc.html">pool allocators</a> use two tag classes to ensure that
the two different allocator types never share the same underlying singleton
pool.</p>
<p><span class="code">Tag</span> is never actually used by <span class=
"code">singleton_pool</span>.</p>
<h3>RequestedSize</h3>
<p>The requested size of memory chunks to allocate. This is passed as a
constructor parameter to the underlying <span class="code">pool</span>.
Must be greater than 0.</p>
<h3>UserAllocator</h3>
<p>Defines the method that the underlying <span class="code">pool</span>
will use to allocate memory from the system. See <a href=
"user_allocator.html">User Allocators</a> for details.</p>
<h2>Semantics</h2>
<table border align="center" summary="">
<caption>
<em>Symbol Table</em>
</caption>
<tr>
<th>Symbol</th>
<th>Meaning</th>
</tr>
<tr>
<td class="code">SingletonPool</td>
<td class="code">singleton_pool<Tag, RequestedSize,
UserAllocator></td>
</tr>
<tr>
<td class="code">chunk</td>
<td>value of type <span class="code">void *</span></td>
</tr>
<tr>
<td class="code">n</td>
<td>value of type <span class="code">size_type</span></td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Typedefs/Static Const Values</em>
</caption>
<tr>
<th>Expression</th>
<th>Type/Value</th>
</tr>
<tr>
<td class="code">SingletonPool::tag</td>
<td class="code">Tag</td>
</tr>
<tr>
<td class="code">SingletonPool::user_allocator</td>
<td class="code">UserAllocator</td>
</tr>
<tr>
<td class="code">SingletonPool::size_type</td>
<td class="code">pool<UserAllocator>::size_type</td>
</tr>
<tr>
<td class="code">SingletonPool::difference_type</td>
<td class="code">pool<UserAllocator>::difference_type</td>
</tr>
<tr>
<td class="code">SingletonPool::requested_size</td>
<td class="code">RequestedSize</td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Functions</em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Semantic Equivalent</th>
</tr>
<tr>
<td class="code">SingletonPool::is_from(chunk)</td>
<td class="code">bool</td>
<td><span class="code">SingletonPool::p.is_from(chunk);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::malloc()</td>
<td class="code">void *</td>
<td><span class="code">SingletonPool::p.malloc();</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::ordered_malloc(n)</td>
<td class="code">void *</td>
<td><span class="code">SingletonPool::p.ordered_malloc(n);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::free(chunk)</td>
<td class="code">void</td>
<td><span class="code">SingletonPool::p.free(chunk);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::ordered_free(chunk)</td>
<td class="code">void</td>
<td><span class="code">SingletonPool::p.ordered_free(chunk);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::free(chunk, n)</td>
<td class="code">void</td>
<td><span class="code">SingletonPool::p.free(chunk, n);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::ordered_free(chunk, n)</td>
<td class="code">void</td>
<td><span class="code">SingletonPool::p.ordered_free(chunk, n);</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::release_memory()</td>
<td class="code">bool</td>
<td><span class="code">SingletonPool::p.release_memory();</span>
synchronized</td>
</tr>
<tr>
<td class="code">SingletonPool::purge_memory()</td>
<td class="code">bool</td>
<td><span class="code">SingletonPool::p.purge_memory();</span>
synchronized</td>
</tr>
</table>
<p>For more information on the semantics of these functions, see the
<a href="pool.html">pool interface</a>.</p>
<h2>Symbols</h2>
<ul>
<li>boost::singleton_pool</li>
</ul>
<h2><a href="../implementation/singleton_pool.html">Implementation
Details</a></h2>
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<p>Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
<p><i>Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT com)</i></p>
<p><i>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
or copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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