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<div class="section" id="mfs-manual-fixed-small">
<span id="pool-mfs"></span><span id="index-0"></span><h1>9. MFS (Manual Fixed Small)<a class="headerlink" href="#mfs-manual-fixed-small" title="Permalink to this headline"></a></h1>
<p><strong>MFS</strong> is an <a class="reference internal" href="../glossary/m.html#term-manual-memory-management"><em class="xref std std-term">manually managed</em></a>
<a class="reference internal" href="../glossary/p.html#term-pool-class"><em class="xref std std-term">pool class</em></a> for small objects of fixed size.</p>
<p>Unlike other manual pool classes, it is not subject to <a class="reference internal" href="../glossary/i.html#term-internal-fragmentation"><em class="xref std std-term">internal
fragmentation</em></a>.</p>
<p>The implementation is very simple: unlike other <a class="reference internal" href="../glossary/p.html#term-pool-class"><em class="xref std std-term">pool classes</em></a>
which store their control structures separately from the allocated
blocks, MFS maintains a stack of free blocks using a pointer in the
free block. <a class="reference internal" href="../topic/allocation.html#mps_alloc" title="mps_alloc"><tt class="xref c c-func docutils literal"><span class="pre">mps_alloc()</span></tt></a> pops this stack and <a class="reference internal" href="../topic/allocation.html#mps_free" title="mps_free"><tt class="xref c c-func docutils literal"><span class="pre">mps_free()</span></tt></a>
pushes it.</p>
<div class="section" id="mfs-properties">
<span id="index-1"></span><h2>9.1. MFS properties<a class="headerlink" href="#mfs-properties" title="Permalink to this headline"></a></h2>
<ul class="simple">
<li>Supports allocation via <a class="reference internal" href="../topic/allocation.html#mps_alloc" title="mps_alloc"><tt class="xref c c-func docutils literal"><span class="pre">mps_alloc()</span></tt></a> and deallocation via
<a class="reference internal" href="../topic/allocation.html#mps_free" title="mps_free"><tt class="xref c c-func docutils literal"><span class="pre">mps_free()</span></tt></a>.</li>
<li>Does not support allocation via <a class="reference internal" href="../glossary/a.html#term-allocation-point"><em class="xref std std-term">allocation points</em></a>.</li>
<li>Does not support <a class="reference internal" href="../glossary/a.html#term-allocation-frame"><em class="xref std std-term">allocation frames</em></a>.</li>
<li>Supports <a class="reference internal" href="../glossary/s.html#term-segregated-allocation-cache"><em class="xref std std-term">segregated allocation caches</em></a> (but using one would
be pointless, since all blocks are the same size).</li>
<li>There are no garbage collections in this pool.</li>
<li>Blocks may not contain <a class="reference internal" href="../glossary/r.html#term-reference"><em class="xref std std-term">references</em></a> to blocks in automatically
managed pools (unless these are registered as <a class="reference internal" href="../glossary/r.html#term-root"><em class="xref std std-term">roots</em></a>).</li>
<li>Allocations are fixed in size.</li>
<li>The <a class="reference internal" href="../glossary/a.html#term-alignment"><em class="xref std std-term">alignment</em></a> of blocks is not configurable: it is the
<a class="reference internal" href="../glossary/n.html#term-natural-alignment"><em class="xref std std-term">natural alignment</em></a> of the platform (see
<a class="reference internal" href="../topic/platform.html#MPS_PF_ALIGN" title="MPS_PF_ALIGN"><tt class="xref c c-macro docutils literal"><span class="pre">MPS_PF_ALIGN</span></tt></a>).</li>
<li>Blocks do not have <a class="reference internal" href="../glossary/d.html#term-dependent-object"><em class="xref std std-term">dependent objects</em></a>.</li>
<li>Blocks are not automatically <a class="reference internal" href="../glossary/r.html#term-reclaim"><em class="xref std std-term">reclaimed</em></a>.</li>
<li>Blocks are not <a class="reference internal" href="../glossary/s.html#term-scan"><em class="xref std std-term">scanned</em></a>.</li>
<li>Blocks are not protected by <a class="reference internal" href="../glossary/b.html#term-barrier-1"><em class="xref std std-term">barriers<sup>(1)</sup></em></a>.</li>
<li>Blocks do not <a class="reference internal" href="../glossary/m.html#term-moving-garbage-collector"><em class="xref std std-term">move</em></a>.</li>
<li>Blocks may not be registered for <a class="reference internal" href="../glossary/f.html#term-finalization"><em class="xref std std-term">finalization</em></a>.</li>
<li>Blocks must not belong to an <a class="reference internal" href="../glossary/o.html#term-object-format"><em class="xref std std-term">object format</em></a>.</li>
</ul>
</div>
<div class="section" id="mfs-interface">
<span id="index-2"></span><h2>9.2. MFS interface<a class="headerlink" href="#mfs-interface" title="Permalink to this headline"></a></h2>
<div class="highlight-c"><div class="highlight"><pre><span class="cp">#include &quot;mpscmfs.h&quot;</span>
</pre></div>
</div>
<dl class="function">
<dt id="mps_class_mfs">
<a class="reference internal" href="../topic/pool.html#mps_class_t" title="mps_class_t">mps_class_t</a> <tt class="descname">mps_class_mfs</tt><big>(</big>void<big>)</big><a class="headerlink" href="#mps_class_mfs" title="Permalink to this definition"></a></dt>
<dd><p>Return the <a class="reference internal" href="../glossary/p.html#term-pool-class"><em class="xref std std-term">pool class</em></a> for an MFS (Manual Fixed Small)
<a class="reference internal" href="../glossary/p.html#term-pool"><em class="xref std std-term">pool</em></a>.</p>
<p>When creating an MFS pool, <a class="reference internal" href="../topic/pool.html#mps_pool_create_k" title="mps_pool_create_k"><tt class="xref c c-func docutils literal"><span class="pre">mps_pool_create_k()</span></tt></a> requires
one <a class="reference internal" href="../glossary/k.html#term-keyword-argument"><em class="xref std std-term">keyword arguments</em></a>:</p>
<ul class="simple">
<li><tt class="xref c c-macro docutils literal"><span class="pre">MPS_KEY_MFS_UNIT_SIZE</span></tt> (type <tt class="xref c c-type docutils literal"><span class="pre">size_t</span></tt>) is the
<a class="reference internal" href="../glossary/s.html#term-size"><em class="xref std std-term">size</em></a> of blocks that will be allocated from this pool, in
<a class="reference internal" href="../glossary/b.html#term-byte-1"><em class="xref std std-term">bytes<sup>(1)</sup></em></a>. It must be at least one <a class="reference internal" href="../glossary/w.html#term-word"><em class="xref std std-term">word</em></a>.</li>
</ul>
<p>In addition, <a class="reference internal" href="../topic/pool.html#mps_pool_create_k" title="mps_pool_create_k"><tt class="xref c c-func docutils literal"><span class="pre">mps_pool_create_k()</span></tt></a> may take:</p>
<ul class="simple">
<li><a class="reference internal" href="../design/poolmvff.html#MPS_KEY_EXTEND_BY" title="MPS_KEY_EXTEND_BY"><tt class="xref c c-macro docutils literal"><span class="pre">MPS_KEY_EXTEND_BY</span></tt></a> (type <tt class="xref c c-type docutils literal"><span class="pre">size_t</span></tt>, default 65536) is the
<a class="reference internal" href="../glossary/s.html#term-size"><em class="xref std std-term">size</em></a> of segment that the pool will request from the
<a class="reference internal" href="../glossary/a.html#term-arena"><em class="xref std std-term">arena</em></a>. It must be at least as big as the unit size
specified by the <tt class="xref c c-macro docutils literal"><span class="pre">MPS_KEY_MFS_UNIT_SIZE</span></tt> keyword
argument. If this is not a multiple of the unit size, there will
be wasted space in each segment.</li>
</ul>
<p>For example:</p>
<div class="highlight-c"><div class="highlight"><pre><span class="n">MPS_ARGS_BEGIN</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{</span>
<span class="n">MPS_ARGS_ADD</span><span class="p">(</span><span class="n">ARGS</span><span class="p">,</span> <span class="n">MPS_KEY_MFS_UNIT_SIZE</span><span class="p">,</span> <span class="mi">1024</span><span class="p">);</span>
<span class="n">MPS_ARGS_ADD</span><span class="p">(</span><span class="n">ARGS</span><span class="p">,</span> <span class="n">MPS_KEY_EXTEND_BY</span><span class="p">,</span> <span class="mi">1024</span> <span class="o">*</span> <span class="mi">1024</span><span class="p">);</span>
<span class="n">MPS_ARGS_DONE</span><span class="p">(</span><span class="n">args</span><span class="p">);</span>
<span class="n">res</span> <span class="o">=</span> <span class="n">mps_pool_create_k</span><span class="p">(</span><span class="o">&amp;</span><span class="n">pool</span><span class="p">,</span> <span class="n">arena</span><span class="p">,</span> <span class="n">mps_class_mfs</span><span class="p">(),</span> <span class="n">args</span><span class="p">);</span>
<span class="p">}</span> <span class="n">MPS_ARGS_END</span><span class="p">(</span><span class="n">args</span><span class="p">);</span>
</pre></div>
</div>
<div class="admonition-deprecated admonition">
<p class="first admonition-title">Deprecated</p>
<p>starting with version 1.112.</p>
<p>When using <a class="reference internal" href="../topic/pool.html#mps_pool_create" title="mps_pool_create"><tt class="xref c c-func docutils literal"><span class="pre">mps_pool_create()</span></tt></a>, pass the segment size and
unit size like this:</p>
<div class="last highlight-c"><div class="highlight"><pre><span class="n">mps_res_t</span> <span class="n">mps_pool_create</span><span class="p">(</span><span class="n">mps_pool_t</span> <span class="o">*</span><span class="n">pool_o</span><span class="p">,</span> <span class="n">mps_arena_t</span> <span class="n">arena</span><span class="p">,</span>
<span class="n">mps_class_t</span> <span class="n">mps_class_mfs</span><span class="p">(),</span>
<span class="n">mps_size_t</span> <span class="n">extend_size</span><span class="p">,</span>
<span class="n">mps_size_t</span> <span class="n">unit_size</span><span class="p">)</span>
</pre></div>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">9. MFS (Manual Fixed Small)</a><ul>
<li><a class="reference internal" href="#mfs-properties">9.1. MFS properties</a></li>
<li><a class="reference internal" href="#mfs-interface">9.2. MFS interface</a></li>
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