ceph/src/boost/libs/context/doc/html/context/econtext/stack/protected_fixedsize.html

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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="context.econtext.stack.protected_fixedsize"></a><a class="link" href="protected_fixedsize.html" title="Class protected_fixedsize">Class
  28         <span class="emphasis"><em>protected_fixedsize</em></span></a>
  29 </h4></div></div></div>
  30 <p>
  31           <span class="bold"><strong>Boost.Context</strong></span> provides the class <span class="emphasis"><em>protected_fixedsize</em></span>
  32           which models the <span class="emphasis"><em>stack-allocator concept</em></span>. It appends
  33           a guard page at the end of each stack to protect against exceeding the
  34           stack. If the guard page is accessed (read or write operation) a segmentation
  35           fault/access violation is generated by the operating system.
  36         </p>
  37 <div class="important"><table border="0" summary="Important">
  38 <tr>
  39 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../../doc/src/images/important.png"></td>
  40 <th align="left">Important</th>
  41 </tr>
  42 <tr><td align="left" valign="top"><p>
  43             Using <span class="emphasis"><em>protected_fixedsize</em></span> is expensive. That is,
  44             launching a new coroutine with a new stack is expensive; the allocated
  45             stack is just as efficient to use as any other stack.
  46           </p></td></tr>
  47 </table></div>
  48 <div class="note"><table border="0" summary="Note">
  49 <tr>
  50 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
  51 <th align="left">Note</th>
  52 </tr>
  53 <tr><td align="left" valign="top"><p>
  54             The appended <code class="computeroutput"><span class="identifier">guard</span> <span class="identifier">page</span></code>
  55             is <span class="bold"><strong>not</strong></span> mapped to physical memory, only
  56             virtual addresses are used.
  57           </p></td></tr>
  58 </table></div>
  59 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">context</span><span class="special">/</span><span class="identifier">protected_fixedsize</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  60
  61 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">traitsT</span> <span class="special">&gt;</span>
  62 <span class="keyword">struct</span> <span class="identifier">basic_protected_fixedsize</span>
  63 <span class="special">{</span>
  64     <span class="keyword">typedef</span> <span class="identifier">traitT</span>  <span class="identifier">traits_type</span><span class="special">;</span>
  65
  66     <span class="identifier">basic_protected_fixesize</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span> <span class="special">=</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">default_size</span><span class="special">());</span>
  67
  68     <span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
  69
  70     <span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">(</span> <span class="identifier">stack_context</span> <span class="special">&amp;);</span>
  71 <span class="special">}</span>
  72
  73 <span class="keyword">typedef</span> <span class="identifier">basic_protected_fixedsize</span><span class="special">&lt;</span> <span class="identifier">stack_traits</span> <span class="special">&gt;</span> <span class="identifier">protected_fixedsize</span>
  74 </pre>
  75 <h6>
  76 <a name="context.econtext.stack.protected_fixedsize.h0"></a>
  77           <span><a name="context.econtext.stack.protected_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"></a></span><a class="link" href="protected_fixedsize.html#context.econtext.stack.protected_fixedsize._code__phrase_role__identifier__stack_context__phrase___phrase_role__identifier__allocate__phrase__phrase_role__special______phrase___code_"><code class="computeroutput"><span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">()</span></code></a>
  78         </h6>
  79 <div class="variablelist">
  80 <p class="title"><b></b></p>
  81 <dl>
  82 <dt><span class="term">Preconditions:</span></dt>
  83 <dd><p>
  84                 <code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">minimum</span><span class="special">:</span><span class="identifier">size</span><span class="special">()</span>
  85                 <span class="special">&lt;=</span> <span class="identifier">size</span></code>
  86                 and <code class="computeroutput"><span class="special">!</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span> <span class="special">&amp;&amp;</span>
  87                 <span class="special">(</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum</span><span class="special">:</span><span class="identifier">size</span><span class="special">()</span> <span class="special">&gt;=</span>
  88                 <span class="identifier">size</span><span class="special">)</span></code>.
  89               </p></dd>
  90 <dt><span class="term">Effects:</span></dt>
  91 <dd><p>
  92                 Allocates memory of at least <code class="computeroutput"><span class="identifier">size</span></code>
  93                 Bytes and stores a pointer to the stack and its actual size in <code class="computeroutput"><span class="identifier">sctx</span></code>. Depending on the architecture
  94                 (the stack grows downwards/upwards) the stored address is the highest/lowest
  95                 address of the stack.
  96               </p></dd>
  97 </dl>
  98 </div>
  99 <h6>
 100 <a name="context.econtext.stack.protected_fixedsize.h1"></a>
 101           <span><a name="context.econtext.stack.protected_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"></a></span><a class="link" href="protected_fixedsize.html#context.econtext.stack.protected_fixedsize._code__phrase_role__keyword__void__phrase___phrase_role__identifier__deallocate__phrase__phrase_role__special_____phrase___phrase_role__identifier__stack_context__phrase___phrase_role__special___amp___phrase___phrase_role__identifier__sctx__phrase__phrase_role__special_____phrase___code_"><code class="computeroutput"><span class="keyword">void</span> <span class="identifier">deallocate</span><span class="special">(</span> <span class="identifier">stack_context</span>
 102           <span class="special">&amp;</span> <span class="identifier">sctx</span><span class="special">)</span></code></a>
 103         </h6>
 104 <div class="variablelist">
 105 <p class="title"><b></b></p>
 106 <dl>
 107 <dt><span class="term">Preconditions:</span></dt>
 108 <dd><p>
 109                 <code class="computeroutput"><span class="identifier">sctx</span><span class="special">.</span><span class="identifier">sp</span></code> is valid, <code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">minimum</span><span class="special">:</span><span class="identifier">size</span><span class="special">()</span> <span class="special">&lt;=</span>
 110                 <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span></code> and <code class="computeroutput"><span class="special">!</span>
 111                 <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
 112                 <span class="special">&amp;&amp;</span> <span class="special">(</span>
 113                 <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum</span><span class="special">:</span><span class="identifier">size</span><span class="special">()</span>
 114                 <span class="special">&gt;=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span><span class="special">)</span></code>.
 115               </p></dd>
 116 <dt><span class="term">Effects:</span></dt>
 117 <dd><p>
 118                 Deallocates the stack space.
 119               </p></dd>
 120 </dl>
 121 </div>
 122 </div>
 123 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 124 <td align="left"></td>
 125 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Oliver Kowalke<p>
 126         Distributed under the Boost Software License, Version 1.0. (See accompanying
 127         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 128       </p>
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