libstdc++-v3/doc/html/manual/bitmap_allocator.html

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 21. The bitmap_allocator</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, allocator" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="extensions.html" title="Part III.  Extensions" /><link rel="prev" href="mt_allocator_ex_multi.html" title="Multiple Thread Example" /><link rel="next" href="bitmap_allocator_impl.html" title="Implementation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 21. The bitmap_allocator</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="mt_allocator_ex_multi.html">Prev</a> </td><th width="60%" align="center">Part III.
   3   Extensions
   4
   5 </th><td width="20%" align="right"> <a accesskey="n" href="bitmap_allocator_impl.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.allocator.bitmap"></a>Chapter 21. The bitmap_allocator</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="bitmap_allocator.html#allocator.bitmap.design">Design</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html">Implementation</a></span></dt><dd><dl><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.free_list_store">Free List Store</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.super_block">Super Block</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.super_block_data">Super Block Data Layout</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.max_wasted">Maximum Wasted Percentage</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.allocate"><code class="function">allocate</code></a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.deallocate"><code class="function">deallocate</code></a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.questions">Questions</a></span></dt><dd><dl><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.question.1">1</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.question.2">2</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.question.3">3</a></span></dt></dl></dd><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.locality">Locality</a></span></dt><dt><span class="section"><a href="bitmap_allocator_impl.html#bitmap.impl.grow_policy">Overhead and Grow Policy</a></span></dt></dl></dd></dl></div><p>
   6 </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="allocator.bitmap.design"></a>Design</h2></div></div></div><p>
   7     As this name suggests, this allocator uses a bit-map to keep track
   8     of the used and unused memory locations for its book-keeping
   9     purposes.
  10   </p><p>
  11     This allocator will make use of 1 single bit to keep track of
  12     whether it has been allocated or not. A bit 1 indicates free,
  13     while 0 indicates allocated. This has been done so that you can
  14     easily check a collection of bits for a free block. This kind of
  15     Bitmapped strategy works best for single object allocations, and
  16     with the STL type parameterized allocators, we do not need to
  17     choose any size for the block which will be represented by a
  18     single bit. This will be the size of the parameter around which
  19     the allocator has been parameterized. Thus, close to optimal
  20     performance will result. Hence, this should be used for node based
  21     containers which call the allocate function with an argument of 1.
  22   </p><p>
  23     The bitmapped allocator's internal pool is exponentially growing.
  24     Meaning that internally, the blocks acquired from the Free List
  25     Store will double every time the bitmapped allocator runs out of
  26     memory.
  27   </p><p>
  28     The macro <code class="literal">__GTHREADS</code> decides whether to use
  29     Mutex Protection around every allocation/deallocation. The state
  30     of the macro is picked up automatically from the gthr abstraction
  31     layer.
  32   </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mt_allocator_ex_multi.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bitmap_allocator_impl.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Multiple Thread Example </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Implementation</td></tr></table></div></body></html>