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

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="context.stack.protected_fixedsize"></a><a class="link" href="protected_fixedsize.html" title="Class protected_fixedsize">Class <span class="emphasis"><em>protected_fixedsize</em></span></a>
  28 </h3></div></div></div>
  29 <p>
  30         <span class="bold"><strong>Boost.Context</strong></span> provides the class <span class="emphasis"><em>protected_fixedsize_stack</em></span>
  31         which models the <span class="emphasis"><em>stack-allocator concept</em></span>. It appends
  32         a guard page at the end of each stack to protect against exceeding the stack.
  33         If the guard page is accessed (read or write operation) a segmentation fault/access
  34         violation is generated by the operating system.
  35       </p>
  36 <div class="important"><table border="0" summary="Important">
  37 <tr>
  38 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../doc/src/images/important.png"></td>
  39 <th align="left">Important</th>
  40 </tr>
  41 <tr><td align="left" valign="top"><p>
  42           Using <span class="emphasis"><em>protected_fixedsize_stack</em></span> is expensive. That
  43           is, launching a new coroutine with a new stack is expensive; the allocated
  44           stack is just as efficient to use as any other stack.
  45         </p></td></tr>
  46 </table></div>
  47 <div class="note"><table border="0" summary="Note">
  48 <tr>
  49 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
  50 <th align="left">Note</th>
  51 </tr>
  52 <tr><td align="left" valign="top"><p>
  53           The appended <code class="computeroutput"><span class="identifier">guard</span> <span class="identifier">page</span></code>
  54           is <span class="bold"><strong>not</strong></span> mapped to physical memory, only
  55           virtual addresses are used.
  56         </p></td></tr>
  57 </table></div>
  58 <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>
  59
  60 <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>
  61 <span class="keyword">struct</span> <span class="identifier">basic_protected_fixedsize</span> <span class="special">{</span>
  62     <span class="keyword">typedef</span> <span class="identifier">traitT</span>  <span class="identifier">traits_type</span><span class="special">;</span>
  63
  64     <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>
  65
  66     <span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
  67
  68     <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>
  69 <span class="special">}</span>
  70
  71 <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>
  72 </pre>
  73 <h5>
  74 <a name="context.stack.protected_fixedsize.h0"></a>
  75         <span><a name="context.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.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>
  76       </h5>
  77 <div class="variablelist">
  78 <p class="title"><b></b></p>
  79 <dl>
  80 <dt><span class="term">Preconditions:</span></dt>
  81 <dd><p>
  82               <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>
  83               <span class="special">&lt;=</span> <span class="identifier">size</span></code>
  84               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>
  85               <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> <span class="identifier">size</span><span class="special">)</span></code>.
  86             </p></dd>
  87 <dt><span class="term">Effects:</span></dt>
  88 <dd><p>
  89               Allocates memory of at least <code class="computeroutput"><span class="identifier">size</span></code>
  90               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
  91               (the stack grows downwards/upwards) the stored address is the highest/lowest
  92               address of the stack.
  93             </p></dd>
  94 </dl>
  95 </div>
  96 <h5>
  97 <a name="context.stack.protected_fixedsize.h1"></a>
  98         <span><a name="context.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.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>
  99         <span class="special">&amp;</span> <span class="identifier">sctx</span><span class="special">)</span></code></a>
 100       </h5>
 101 <div class="variablelist">
 102 <p class="title"><b></b></p>
 103 <dl>
 104 <dt><span class="term">Preconditions:</span></dt>
 105 <dd><p>
 106               <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> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span></code> and <code class="computeroutput"><span class="special">!</span>
 107               <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
 108               <span class="special">&amp;&amp;</span> <span class="special">(</span>
 109               <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>
 110               <span class="special">&gt;=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span><span class="special">)</span></code>.
 111             </p></dd>
 112 <dt><span class="term">Effects:</span></dt>
 113 <dd><p>
 114               Deallocates the stack space.
 115             </p></dd>
 116 </dl>
 117 </div>
 118 </div>
 119 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 120 <td align="left"></td>
 121 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Oliver Kowalke<p>
 122         Distributed under the Boost Software License, Version 1.0. (See accompanying
 123         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>)
 124       </p>
 125 </div></td>
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