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<h1 align="center">pool_alloc - Boost Pool Standard Allocators</h1>
<h2>Introduction</h2>
<p>pool_alloc.hpp provides two template types that can be used for fast and
efficient memory allocation. These types both satisfy the Standard
Allocator requirements [20.1.5] and the additional requirements in
[20.1.5/4], so they can be used with Standard or user-supplied containers.
For information on other pool-based interfaces, see <a href=
"../interfaces.html">the other pool interfaces</a>.</p>
<h2>Synopsis</h2>
<pre class="code">
struct pool_allocator_tag { };
template <typename T,
typename UserAllocator = default_user_allocator_new_delete>
class pool_allocator
{
public:
typedef UserAllocator user_allocator;
typedef T value_type;
typedef value_type * pointer;
typedef const value_type * const_pointer;
typedef value_type & reference;
typedef const value_type & const_reference;
typedef typename pool<UserAllocator>::size_type size_type;
typedef typename pool<UserAllcoator>::difference_type difference_type;
template <typename U>
struct rebind
{ typedef pool_allocator<U, UserAllocator> other; };
public:
pool_allocator();
pool_allocator(const pool_allocator &);
// The following is not explicit, mimicking std::allocator [20.4.1]
template <typename U>
pool_allocator(const pool_allocator<U, UserAllocator> &);
pool_allocator & operator=(const pool_allocator &);
~pool_allocator();
static pointer address(reference r);
static const_pointer address(const_reference s);
static size_type max_size();
static void construct(pointer ptr, const value_type & t);
static void destroy(pointer ptr);
bool operator==(const pool_allocator &) const;
bool operator!=(const pool_allocator &) const;
static pointer allocate(size_type n);
static pointer allocate(size_type n, pointer);
static void deallocate(pointer ptr, size_type n);
};
struct fast_pool_allocator_tag { };
template <typename T
typename UserAllocator = default_user_allocator_new_delete>
class fast_pool_allocator
{
public:
typedef UserAllocator user_allocator;
typedef T value_type;
typedef value_type * pointer;
typedef const value_type * const_pointer;
typedef value_type & reference;
typedef const value_type & const_reference;
typedef typename pool<UserAllocator>::size_type size_type;
typedef typename pool<UserAllocator>::difference_type difference_type;
template <typename U>
struct rebind
{ typedef fast_pool_allocator<U, UserAllocator> other; };
public:
fast_pool_allocator();
fast_pool_allocator(const fast_pool_allocator &);
// The following is not explicit, mimicking std::allocator [20.4.1]
template <typename U>
fast_pool_allocator(const fast_pool_allocator<U, UserAllocator> &);
fast_pool_allocator & operator=(const fast_pool_allocator &);
~fast_pool_allocator();
static pointer address(reference r);
static const_pointer address(const_reference s);
static size_type max_size();
static void construct(pointer ptr, const value_type & t);
static void destroy(pointer ptr);
bool operator==(const fast_pool_allocator &) const;
bool operator!=(const fast_pool_allocator &) const;
static pointer allocate(size_type n);
static pointer allocate(size_type n, pointer);
static void deallocate(pointer ptr, size_type n);
static pointer allocate();
static void deallocate(pointer ptr);
};
</pre>
<h2>Template Parameters</h2>
<h3>T</h3>
<p>The first template parameter is the type of object to
allocate/deallocate.</p>
<h3>UserAllocator</h3>
<p>Defines the method that the underlying Pool will use to allocate memory
from the system. See <a href="user_allocator.html">User Allocators</a> for
details.</p>
<h2>Semantics</h2>
<p>Both of the pool allocators above satisfy all Standard Allocator
requirements, as laid out in the Standard [20.1.5]. They also both satisfy
the additional requirements found in [20.1.5/4]; this permits their usage
with any Standard-compliant container.</p>
<p>In addition, the <span class="code">fast_pool_allocator</span> also
provides an additional allocation and an additional deallocation
function:</p>
<table border align="center" summary="">
<caption>
<em>Symbol Table</em>
</caption>
<tr>
<th>Symbol</th>
<th>Meaning</th>
</tr>
<tr>
<td class="code">PoolAlloc</td>
<td><span class="code">fast_pool_allocator<T,
UserAllocator></span></td>
</tr>
<tr>
<td class="code">p</td>
<td>value of type <span class="code">T *</span></td>
</tr>
</table><br>
<table border align="center" summary="">
<caption>
<em>Additional allocation/deallocation functions (<span class=
"code">fast_pool_allocator</span> only)</em>
</caption>
<tr>
<th>Expression</th>
<th>Return Type</th>
<th>Semantic Equivalence</th>
</tr>
<tr>
<td class="code">PoolAlloc::allocate()</td>
<td class="code">T *</td>
<td class="code">PoolAlloc::allocate(1)</td>
</tr>
<tr>
<td class="code">PoolAlloc::deallocate(p)</td>
<td>void</td>
<td class="code">PoolAlloc::deallocate(p, 1)</td>
</tr>
</table>
<p>The typedef <span class="code">user_allocator</span> publishes the value
of the <span class="code">UserAllocator</span> template parameter.</p>
<h2>Notes</h2>
<p>If the allocation functions run out of memory, they will throw
<span class="code">std::bad_alloc</span>.</p>
<p>The underlying Pool type used by the allocators is accessible through
the <a href="singleton_pool.html">Singleton Pool Interface</a>. The
identifying tag used for <span class="code">pool_allocator</span> is
<span class="code">pool_allocator_tag</span>, and the tag used for
<span class="code">fast_pool_allocator</span> is <span class=
"code">fast_pool_allocator_tag</span>. All template parameters of the
allocators (including <a href=
"../implementation/pool_alloc.html">implementation-specific ones</a>)
determine the type of the underlying Pool, with the exception of the first
parameter <span class="code">T</span>, whose size is used instead.</p>
<p>Since the size of <span class="code">T</span> is used to determine the
type of the underlying Pool, each allocator for different types of the same
size <em>will share</em> the same underlying pool. The tag class prevents
pools from being shared between <span class="code">pool_allocator</span>
and <span class="code">fast_pool_allocator</span>. For example, on a system
where sizeof(int) == sizeof(void *), <span class=
"code">pool_allocator<int></span> and <span class=
"code">pool_allocator<void *></span> will both allocate/deallocate
from/to the same pool.</p>
<p>If there is only one thread running before <span class=
"code">main()</span> starts and after <span class="code">main()</span>
ends, then both allocators are completely thread-safe.</p>
<h2>The Fast Pool Allocator</h2>
<p><span class="code">pool_allocator</span> is a more general-purpose
solution, geared towards efficiently servicing requests for any number of
contiguous chunks. <span class="code">fast_pool_allocator</span> is also a
general-purpose solution, but is geared towards efficiently servicing
requests for one chunk at a time; it will work for contiguous chunks, but
not as well as <span class="code">pool_allocator</span>. If you are
seriously concerned about performance, use <span class=
"code">fast_pool_allocator</span> when dealing with containers such as
<span class="code">std::list</span>, and use <span class=
"code">pool_allocator</span> when dealing with containers such as
<span class="code">std::vector</span>.</p>
<h2>Symbols</h2>
<ul>
<li>boost::pool_allocator</li>
<li>boost::pool_allocator_tag</li>
<li>boost::fast_pool_allocator</li>
<li>boost::fast_pool_allocator_tag</li>
</ul>
<h2><a href="../implementation/pool_alloc.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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