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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>
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.
37 <div class=
"important"><table border=
"0" summary=
"Important">
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>
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.
48 <div class=
"note"><table border=
"0" summary=
"Note">
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>
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.
59 <pre class=
"programlisting"><span class=
"preprocessor">#include
</span> <span class=
"special"><</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">></span>
61 <span class=
"keyword">template
</span><span class=
"special"><</span> <span class=
"keyword">typename
</span> <span class=
"identifier">traitsT
</span> <span class=
"special">></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>
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>
68 <span class=
"identifier">stack_context
</span> <span class=
"identifier">allocate
</span><span class=
"special">();
</span>
70 <span class=
"keyword">void
</span> <span class=
"identifier">deallocate
</span><span class=
"special">(
</span> <span class=
"identifier">stack_context
</span> <span class=
"special">&);
</span>
71 <span class=
"special">}
</span>
73 <span class=
"keyword">typedef
</span> <span class=
"identifier">basic_protected_fixedsize
</span><span class=
"special"><</span> <span class=
"identifier">stack_traits
</span> <span class=
"special">></span> <span class=
"identifier">protected_fixedsize
</span>
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>
79 <div class=
"variablelist">
80 <p class=
"title"><b></b></p>
82 <dt><span class=
"term">Preconditions:
</span></dt>
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"><=
</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">&&</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">>=
</span>
88 <span class=
"identifier">size
</span><span class=
"special">)
</span></code>.
90 <dt><span class=
"term">Effects:
</span></dt>
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
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">&</span> <span class=
"identifier">sctx
</span><span class=
"special">)
</span></code></a>
104 <div class=
"variablelist">
105 <p class=
"title"><b></b></p>
107 <dt><span class=
"term">Preconditions:
</span></dt>
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"><=
</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">&&</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">>=
</span> <span class=
"identifier">sctx
</span><span class=
"special">.
</span><span class=
"identifier">size
</span><span class=
"special">)
</span></code>.
116 <dt><span class=
"term">Effects:
</span></dt>
118 Deallocates the stack space.
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
© 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>)
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