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  <img src="../../../../boost.png" width="276" height="86" alt="C++ Boost">

  <h1 align="center">Pool Implementation</h1>

  <h2>Dependencies</h2>

  <p>Includes the system headers <span class=
  "code">&lt;functional&gt;</span>, <span class="code">&lt;new&gt;</span>,
  <span class="code">&lt;cstddef&gt;</span>, <span class=
  "code">&lt;cstdlib&gt;</span>, and <span class=
  "code">&lt;exception&gt;</span>.</p>

  <p>Includes the Boost headers <span class=
  "code">"detail/ct_gcd_lcm.hpp"</span> (see <a href=
  "ct_gcd_lcm.html">ct_gcd_lcm.html</a>), <span class=
  "code">"detail/gcd_lcm.hpp"</span> (see <a href=
  "gcd_lcm.html">gcd_lcm.html</a>), and <span class=
  "code">"simple_segregated_storage.hpp"</span> (see <a href=
  "simple_segregated_storage.html">simple_segregated_storage.html</a>).</p>

  <h2>Synopsis</h2>
  <pre class="code">
namespace details {

template &lt;typename SizeType&gt;
class PODptr
{
  public:
    typedef SizeType size_type;

    PODptr(char * ptr, size_type size);
    PODptr();

    // Copy constructor, assignment operator, and destructor allowed

    bool valid() const;
    void invalidate();
    char * &amp; begin();
    char * begin() const;
    char * end() const;
    size_type total_size() const;
    size_type element_size() const;

    size_type &amp; next_size() const;
    char * &amp; next_ptr() const;

    PODptr next() const;
    void next(const PODptr &amp; arg) const;
};

} // namespace details

template &lt;typename UserAllocator = default_user_allocator_new_delete&gt;
class pool: protected simple_segregated_storage&lt;typename UserAllocator::size_type&gt;
{
  ... // public interface

  protected:
    details::PODptr&lt;size_type&gt; list;

    simple_segregated_storage&lt;size_type&gt; &amp; store();
    const simple_segregated_storage&lt;size_type&gt; &amp; store() const;

    const size_type requested_size;
    size_type next_size;

    details::PODptr&lt;size_type&gt; find_POD(void * chunk) const;
    static bool is_from(void * chunk, char * i, size_type sizeof_i);
    size_type alloc_size() const;

  public: // extensions to public interface
    pool(size_type requested_size, size_type next_size);
    size_type get_next_size() const;
    void set_next_size(size_type);
};
</pre>

  <h2>Extensions to Public Interface</h2>

  <p>Whenever an object of type <span class="code">pool</span> needs memory
  from the system, it will request it from its <span class=
  "code">UserAllocator</span> template parameter. The amount requested is
  determined using a doubling algorithm; that is, each time more system
  memory is allocated, the amount of system memory requested is doubled.
  Users may control the doubling algorithm by using the following
  extensions.</p>

  <h3>Additional constructor parameter</h3>

  <p>Users may pass an additional constructor parameter to <span class=
  "code">pool</span>. This parameter is of type <span class=
  "code">size_type</span>, and is the number of chunks to request from the
  system the first time that object needs to allocate system memory. The
  default is 32. This parameter may not be 0.</p>

  <h3><span class="code">next_size</span> accessor functions</h3>

  <p>The pair of functions <span class="code">size_type get_next_size()
  const;</span> and <span class="code">void set_next_size(size_type);</span>
  allow users to explicitly read and write the <span class=
  "code">next_size</span> value. This value is the number of chunks to
  request from the system the next time that object needs to allocate system
  memory. This value should never be set to 0.</p>

  <h2>Class <span class="code">PODptr</span></h2>

  <p><span class="code">PODptr</span> is a class that pretends to be a
  "pointer" to different class types that don't really exist. It provides
  member functions to access the "data" of the "object" it points to. Since
  these "class" types are of differing sizes, and contain some information at
  the end of their memory (for alignment reasons), <span class=
  "code">PODptr</span> must contain the size of this "class" as well as the
  pointer to this "object".</p>

  <p>A <span class="code">PODptr</span> holds the location and size of a
  memory block allocated from the system. Each memory block is split
  logically into three sections:</p>

  <ol>
    <li>Chunk area. This section may be different sizes. <span class=
    "code">PODptr</span> does not care what the size of the chunks is, but it
    does care (and keep track of) the total size of the chunk area.</li>

    <li>Next pointer. This section is always the same size for a given
    <span class="code">SizeType</span>. It holds a pointer to the location of
    the next memory block in the memory block list, or 0 if there is no such
    block.</li>

    <li>Next size. This section is always the same size for a given
    <span class="code">SizeType</span>. It holds the size of the next memory
    block in the memory block list.</li>
  </ol>

  <p>The <span class="code">PODptr</span> class just provides cleaner ways of
  dealing with raw memory blocks.</p>

  <h3>Validity</h3>

  <p>A <span class="code">PODptr</span> object is either <em>valid</em> or
  <em>invalid</em>. An invalid <span class="code">PODptr</span> is analogous
  to a null pointer.</p>

  <p>The default constructor for <span class="code">PODptr</span> will result
  in an invalid object. Calling the member function <span class=
  "code">invalidate</span> will result in that object becoming invalid. The
  member function <span class="code">valid</span> can be used to test for
  validity.</p>

  <h3>Getting <span class="code">PODptr</span> objects</h3>

  <p>A <span class="code">PODptr</span> may be created to point to a memory
  block by passing the address and size of that memory block into the
  constructor. A <span class="code">PODptr</span> constructed in this way is
  valid.</p>

  <p>A <span class="code">PODptr</span> may also be created by a call to the
  member function <span class="code">next</span>, which returns a
  <span class="code">PODptr</span> which points to the next memory block in
  the memory block list, or an invalid <span class="code">PODptr</span> if
  there is no such block.</p>

  <h3>Accessing the "pointer" data</h3>

  <p>Each <span class="code">PODptr</span> keeps the address and size of its
  memory block. The address may be read or written by the member functions
  <span class="code">begin</span>. The size of the memory block may only be
  read, and is done so by the member function <span class=
  "code">total_size</span>.</p>

  <h3>Accessing the sections of the memory block</h3>

  <p>The chunk area may be accessed by the member functions <span class=
  "code">begin</span> and <span class="code">end</span>, in conjunction with
  <span class="code">element_size</span>. The value returned by <span class=
  "code">end</span> is always the value returned by <span class=
  "code">begin</span> plus <span class="code">element_size</span>. Only
  <span class="code">begin</span> is writeable. <span class="code">end</span>
  is a past-the-end value; using pointers beginning at <span class=
  "code">begin</span> and ending before <span class="code">end</span> allows
  one to iterate through the chunks in a memory block.</p>

  <p>The next pointer area may be accessed by the member function
  <span class="code">next_ptr</span>. The next size area may be accessed by
  the member function <span class="code">next_size</span>. Both of these are
  writeable. They may both be read or set at the same time through the member
  function <span class="code">next</span>.</p>

  <h2>Protected Interface</h2>

  <h3>Protected Derivation</h3>Pool derives from a simple segregated storage
  via protected derivation; this exposes all the <a href=
  "simple_segregated_storage.html">simple segregated storage implementation
  details</a> to all classes derived from Pool as well.

  <h3 class="code">details::PODptr&lt;size_type&gt; list;</h3>

  <p>This is the list of memory blocks that have been allocated by this Pool
  object. It is <strong>not</strong> the same as the list of free memory
  chunks (exposed by simple segregated storage as <span class=
  "code">first</span>).</p>

  <h3><span class="code">store</span> functions</h3>

  <p>These are convenience functions, used to return the base simple
  segregated storage object.</p>

  <h3 class="code">const size_type requested_size;</h3>

  <p>The first argument passed into the constructor. Represents the number of
  bytes in each chunk requested by the user. The actual size of the chunks
  may be different; see <span class="code">alloc_size</span>, below.</p>

  <h3 class="code">size_type next_size</h3>

  <p>The number of chunks to request from the <span class=
  "code">UserAllocator</span> the next time we need to allocate system
  memory. See the extensions descriptions, above.</p>

  <h3 class="code">details::PODptr&lt;size_type&gt; find_POD(void * chunk)
  const;</h3>

  <p>Searches through the memory block list, looking for the block that
  <span class="code">chunk</span> was allocated from or may be allocated from
  in the future. Returns that block if found, or an invalid value if
  <span class="code">chunk</span> has been allocated from another Pool or may
  be allocated from another Pool in the future. Results for other values of
  <span class="code">chunk</span> may be wrong.</p>

  <h3 class="code">static bool is_from(void * chunk, char * i, size_type
  sizeof_i);</h3>

  <p>Tests <span class="code">chunk</span> to see if it has been allocated
  from the memory chunk at <span class="code">i</span> with an element size
  of <span class="code">sizeof_i</span>. Note that <span class=
  "code">sizeof_i</span> is the size of the chunk area of that block, not the
  total size of that block.</p>

  <p>Returns <span class="code">true</span> if <span class=
  "code">chunk</span> has been allocated from that memory block or may be
  allocated from that block in the future. Returns <span class=
  "code">false</span> if <span class="code">chunk</span> has been allocated
  from another block or may be allocated from another block in the future.
  Results for other values of <span class="code">chunk</span> may be
  wrong.</p>

  <h3 class="code">size_type alloc_size() const;</h3>

  <p>Returns the calculated size of the memory chunks that will be allocated
  by this Pool. For <a href="alignment.html">alignment reasons</a>, this is
  defined to be <span class="code">lcm(requested_size, sizeof(void *),
  sizeof(size_type))</span>.</p>

  <h2><a href="../interfaces/pool.html">Interface Description</a></h2>
  <hr>

  <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
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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 &copy; 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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