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<title>Stack allocation</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fiber.stack"></a><a name="stack"></a><a class="link" href="stack.html" title="Stack allocation">Stack allocation</a>
</h2></div></div></div>
<p>
A <a class="link" href="fiber_mgmt/fiber.html#class_fiber"> <code class="computeroutput">fiber</code></a> uses internally an <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/econtext.html" target="_top"><span class="emphasis"><em>execution_context</em></span></a>
which manages a set of registers and a stack. The memory used by the stack
is allocated/deallocated via a <span class="emphasis"><em>stack_allocator</em></span> which is
required to model a <a class="link" href="stack.html#stack_allocator_concept"><span class="emphasis"><em>stack-allocator
concept</em></span></a>.
</p>
<p>
A <span class="emphasis"><em>stack_allocator</em></span> can be passed to <a class="link" href="fiber_mgmt/fiber.html#fiber_fiber"><code class="computeroutput"><span class="identifier">fiber</span><span class="special">::</span><span class="identifier">fiber</span><span class="special">()</span></code></a> or to <a class="link" href="synchronization/futures/future.html#fibers_async"> <code class="computeroutput">fibers::async()</code></a>.
</p>
<a name="stack_allocator_concept"></a><h4>
<a name="fiber.stack.h0"></a>
<span><a name="fiber.stack.stack_allocator_concept"></a></span><a class="link" href="stack.html#fiber.stack.stack_allocator_concept">stack-allocator
concept</a>
</h4>
<p>
A <span class="emphasis"><em>stack_allocator</em></span> must satisfy the <span class="emphasis"><em>stack-allocator
concept</em></span> requirements shown in the following table, in which <code class="computeroutput"><span class="identifier">a</span></code> is an object of a <span class="emphasis"><em>stack_allocator</em></span>
type, <code class="computeroutput"><span class="identifier">sctx</span></code> is a <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack/stack_context.html" target="_top"><code class="computeroutput"><span class="identifier">stack_context</span></code></a>, and <code class="computeroutput"><span class="identifier">size</span></code> is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span></code>:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
return type
</p>
</th>
<th>
<p>
notes
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">(</span><span class="identifier">size</span><span class="special">)</span></code>
</p>
</td>
<td>
</td>
<td>
<p>
creates a stack allocator
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">()</span></code>
</p>
</td>
<td>
<p>
<a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack/stack_context.html" target="_top"><code class="computeroutput"><span class="identifier">stack_context</span></code></a>
</p>
</td>
<td>
<p>
creates a stack
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">deallocate</span><span class="special">(</span>
<span class="identifier">sctx</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
deallocates the stack created by <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">allocate</span><span class="special">()</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>
The implementation of <code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code> might include logic to protect against
exceeding the context's available stack size rather than leaving it as undefined
behaviour.
</p></td></tr>
</table></div>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>
Calling <code class="computeroutput"><span class="identifier">deallocate</span><span class="special">()</span></code>
with a <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack/stack_context.html" target="_top"><code class="computeroutput"><span class="identifier">stack_context</span></code></a> not obtained from
<code class="computeroutput"><span class="identifier">allocate</span><span class="special">()</span></code>
results in undefined behaviour.
</p></td></tr>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
The memory for the stack is not required to be aligned; alignment takes place
inside <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/econtext.html" target="_top"><span class="emphasis"><em>execution_context</em></span></a>.
</p></td></tr>
</table></div>
<p>
See also <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack.html" target="_top">Boost.Context
stack allocation</a>. In particular, <code class="computeroutput"><span class="identifier">traits_type</span></code>
methods are as described for <a href="http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack/stack_traits.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">stack_traits</span></code></a>.
</p>
<p>
</p>
<h5>
<a name="class_protected_fixedsize_stack_bridgehead"></a>
<span><a name="class_protected_fixedsize_stack"></a></span>
<a class="link" href="stack.html#class_protected_fixedsize_stack">Class
<code class="computeroutput">protected_fixedsize_stack</code></a>
</h5>
<p>
</p>
<p>
<span class="bold"><strong>Boost.Fiber</strong></span> provides the class <a class="link" href="stack.html#class_protected_fixedsize_stack"> <code class="computeroutput">protected_fixedsize_stack</code></a> which
models the <a class="link" href="stack.html#stack_allocator_concept"><span class="emphasis"><em>stack-allocator
concept</em></span></a>. It appends a guard page at the end of each stack
to protect against exceeding the stack. If the guard page is accessed (read
or write operation) a segmentation fault/access violation is generated by the
operating system.
</p>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top"><p>
Using <a class="link" href="stack.html#class_protected_fixedsize_stack"> <code class="computeroutput">protected_fixedsize_stack</code></a> is expensive.
Launching a new fiber with a stack of this type incurs the overhead of setting
the memory protection; once allocated, this stack is just as efficient to
use as <a class="link" href="stack.html#class_fixedsize_stack"> <code class="computeroutput">fixedsize_stack</code></a>.
</p></td></tr>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
The appended <code class="computeroutput"><span class="identifier">guard</span> <span class="identifier">page</span></code>
is <span class="bold"><strong>not</strong></span> mapped to physical memory, only virtual
addresses are used.
</p></td></tr>
</table></div>
<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">fiber</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>
<span class="keyword">struct</span> <span class="identifier">protected_fixedsize</span> <span class="special">{</span>
<span class="identifier">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>
<span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
<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>
<span class="special">}</span>
</pre>
<p>
</p>
<h5>
<a name="protected_fixedsize_allocate_bridgehead"></a>
<span><a name="protected_fixedsize_allocate"></a></span>
<a class="link" href="stack.html#protected_fixedsize_allocate">Member
function <code class="computeroutput">allocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">minimum_size</span><span class="special">()</span>
<span class="special">&lt;=</span> <span class="identifier">size</span></code>
and <code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
<span class="special">||</span> <span class="special">(</span>
<span class="identifier">size</span> <span class="special">&lt;=</span>
<span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span>
<span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Allocates memory of at least <code class="computeroutput"><span class="identifier">size</span></code>
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
(the stack grows downwards/upwards) the stored address is the highest/lowest
address of the stack.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="protected_fixesize_deallocate_bridgehead"></a>
<span><a name="protected_fixesize_deallocate"></a></span>
<a class="link" href="stack.html#protected_fixesize_deallocate">Member
function <code class="computeroutput">deallocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><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> <span class="identifier">sctx</span><span class="special">);</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<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_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="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span> <span class="special">||</span> <span class="special">(</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span> <span class="special">&lt;=</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span> <span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Deallocates the stack space.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="class_pooled_fixedsize_stack_bridgehead"></a>
<span><a name="class_pooled_fixedsize_stack"></a></span>
<a class="link" href="stack.html#class_pooled_fixedsize_stack">Class
<code class="computeroutput">pooled_fixedsize_stack</code></a>
</h5>
<p>
</p>
<p>
<span class="bold"><strong>Boost.Fiber</strong></span> provides the class <a class="link" href="stack.html#class_pooled_fixedsize_stack"> <code class="computeroutput">pooled_fixedsize_stack</code></a> which
models the <a class="link" href="stack.html#stack_allocator_concept"><span class="emphasis"><em>stack-allocator
concept</em></span></a>. In contrast to <a class="link" href="stack.html#class_protected_fixedsize_stack"> <code class="computeroutput">protected_fixedsize_stack</code></a> it
does not append a guard page at the end of each stack. The memory is managed
internally by <a href="http://www.boost.org/doc/libs/release/libs/pool/doc/html/boost/pool.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">pool</span><span class="special">&lt;&gt;</span></code></a>.
</p>
<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">fiber</span><span class="special">/</span><span class="identifier">pooled_fixedsize_stack</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">pooled_fixedsize_stack</span> <span class="special">{</span>
<span class="identifier">pooled_fixedsize_stack</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">stack_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> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">next_size</span> <span class="special">=</span> <span class="number">32</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
<span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
<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>
<span class="special">}</span>
</pre>
<p>
</p>
<h5>
<a name="pooled_fixedsize_bridgehead"></a>
<span><a name="pooled_fixedsize"></a></span>
<a class="link" href="stack.html#pooled_fixedsize">Constructor</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="identifier">pooled_fixedsize_stack</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">stack_size</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">next_size</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">max_size</span><span class="special">);</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
<span class="special">||</span> <span class="special">(</span>
<span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span>
<span class="special">&gt;=</span> <span class="identifier">stack_size</span><span class="special">)</span></code> and <code class="computeroutput"><span class="number">0</span>
<span class="special">&lt;</span> <span class="identifier">next_size</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Allocates memory of at least <code class="computeroutput"><span class="identifier">stack_size</span></code>
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
(the stack grows downwards/upwards) the stored address is the highest/lowest
address of the stack. Argument <code class="computeroutput"><span class="identifier">next_size</span></code>
determines the number of stacks to request from the system the first
time that <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
needs to allocate system memory. The third argument <code class="computeroutput"><span class="identifier">max_size</span></code>
controls how much memory might be allocated for stacks &#8212; a value of zero
means no upper limit.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="pooled_fixedsize_allocate_bridgehead"></a>
<span><a name="pooled_fixedsize_allocate"></a></span>
<a class="link" href="stack.html#pooled_fixedsize_allocate">Member
function <code class="computeroutput">allocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
<span class="special">||</span> <span class="special">(</span>
<span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span>
<span class="special">&gt;=</span> <span class="identifier">stack_size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Allocates memory of at least <code class="computeroutput"><span class="identifier">stack_size</span></code>
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
(the stack grows downwards/upwards) the stored address is the highest/lowest
address of the stack.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="pooled_fixesize_deallocate_bridgehead"></a>
<span><a name="pooled_fixesize_deallocate"></a></span>
<a class="link" href="stack.html#pooled_fixesize_deallocate">Member
function <code class="computeroutput">deallocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><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> <span class="identifier">sctx</span><span class="special">);</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<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">is_unbounded</span><span class="special">()</span> <span class="special">||</span> <span class="special">(</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span> <span class="special">&gt;=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Deallocates the stack space.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="class_fixedsize_stack_bridgehead"></a>
<span><a name="class_fixedsize_stack"></a></span>
<a class="link" href="stack.html#class_fixedsize_stack">Class
<code class="computeroutput">fixedsize_stack</code></a>
</h5>
<p>
</p>
<p>
<span class="bold"><strong>Boost.Fiber</strong></span> provides the class <a class="link" href="stack.html#class_fixedsize_stack"> <code class="computeroutput">fixedsize_stack</code></a> which
models the <a class="link" href="stack.html#stack_allocator_concept"><span class="emphasis"><em>stack-allocator
concept</em></span></a>. In contrast to <a class="link" href="stack.html#class_protected_fixedsize_stack"> <code class="computeroutput">protected_fixedsize_stack</code></a> it
does not append a guard page at the end of each stack. The memory is simply
managed by <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">malloc</span><span class="special">()</span></code>
and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">free</span><span class="special">()</span></code>.
</p>
<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">fixedsize_stack</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">fixedsize_stack</span> <span class="special">{</span>
<span class="identifier">fixedsize_stack</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>
<span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
<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>
<span class="special">}</span>
</pre>
<p>
</p>
<h5>
<a name="fixedsize_allocate_bridgehead"></a>
<span><a name="fixedsize_allocate"></a></span>
<a class="link" href="stack.html#fixedsize_allocate">Member function
<code class="computeroutput">allocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">minimum_size</span><span class="special">()</span>
<span class="special">&lt;=</span> <span class="identifier">size</span></code>
and <code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
<span class="special">||</span> <span class="special">(</span>
<span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span>
<span class="special">&gt;=</span> <span class="identifier">size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Allocates memory of at least <code class="computeroutput"><span class="identifier">size</span></code>
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
(the stack grows downwards/upwards) the stored address is the highest/lowest
address of the stack.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="fixesize_deallocate_bridgehead"></a>
<span><a name="fixesize_deallocate"></a></span>
<a class="link" href="stack.html#fixesize_deallocate">Member
function <code class="computeroutput">deallocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><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> <span class="identifier">sctx</span><span class="special">);</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<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_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="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span> <span class="special">||</span> <span class="special">(</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span> <span class="special">&gt;=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Deallocates the stack space.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="class_segmented_stack_bridgehead"></a>
<span><a name="class_segmented_stack"></a></span>
<a class="link" href="stack.html#class_segmented_stack">Class
<code class="computeroutput">segmented_stack</code></a>
</h5>
<p>
</p>
<p>
<span class="bold"><strong>Boost.Fiber</strong></span> supports usage of a <a class="link" href="stack.html#class_segmented_stack"> <code class="computeroutput">segmented_stack</code></a>,
i.e. the stack grows on demand. The fiber is created with a minimal stack size
which will be increased as required. Class <a class="link" href="stack.html#class_segmented_stack"> <code class="computeroutput">segmented_stack</code></a> models
the <a class="link" href="stack.html#stack_allocator_concept"><span class="emphasis"><em>stack-allocator concept</em></span></a>.
In contrast to <a class="link" href="stack.html#class_protected_fixedsize_stack"> <code class="computeroutput">protected_fixedsize_stack</code></a> and
<a class="link" href="stack.html#class_fixedsize_stack"> <code class="computeroutput">fixedsize_stack</code></a> it creates a stack which grows on demand.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
Segmented stacks are currently only supported by <span class="bold"><strong>gcc</strong></span>
from version <span class="bold"><strong>4.7</strong></span> and <span class="bold"><strong>clang</strong></span>
from version <span class="bold"><strong>3.4</strong></span> onwards. In order to use
a <a class="link" href="stack.html#class_segmented_stack"> <code class="computeroutput">segmented_stack</code></a> <span class="bold"><strong>Boost.Fiber</strong></span>
must be built with property <code class="computeroutput"><span class="identifier">segmented</span><span class="special">-</span><span class="identifier">stacks</span></code>,
e.g. <span class="bold"><strong>toolset=gcc segmented-stacks=on</strong></span> at
b2/bjam command line.
</p></td></tr>
</table></div>
<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">fiber</span><span class="special">/</span><span class="identifier">segmented_stack</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">segmented_stack</span> <span class="special">{</span>
<span class="identifier">segmented_stack</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">stack_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>
<span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
<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>
<span class="special">}</span>
</pre>
<p>
</p>
<h5>
<a name="segmented_allocate_bridgehead"></a>
<span><a name="segmented_allocate"></a></span>
<a class="link" href="stack.html#segmented_allocate">Member function
<code class="computeroutput">allocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="identifier">stack_context</span> <span class="identifier">allocate</span><span class="special">();</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">minimum_size</span><span class="special">()</span>
<span class="special">&lt;=</span> <span class="identifier">size</span></code>
and <code class="computeroutput"><span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span>
<span class="special">||</span> <span class="special">(</span>
<span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span>
<span class="special">&gt;=</span> <span class="identifier">size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Allocates memory of at least <code class="computeroutput"><span class="identifier">size</span></code>
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
(the stack grows downwards/upwards) the stored address is the highest/lowest
address of the stack.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="segmented_deallocate_bridgehead"></a>
<span><a name="segmented_deallocate"></a></span>
<a class="link" href="stack.html#segmented_deallocate">Member
function <code class="computeroutput">deallocate</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><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> <span class="identifier">sctx</span><span class="special">);</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Preconditions:</span></dt>
<dd><p>
<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_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="identifier">traits_type</span><span class="special">::</span><span class="identifier">is_unbounded</span><span class="special">()</span> <span class="special">||</span> <span class="special">(</span> <span class="identifier">traits_type</span><span class="special">::</span><span class="identifier">maximum_size</span><span class="special">()</span> <span class="special">&gt;=</span> <span class="identifier">sctx</span><span class="special">.</span><span class="identifier">size</span><span class="special">)</span></code>.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Deallocates the stack space.
</p></dd>
</dl>
</div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
If the library is compiled for segmented stacks, <a class="link" href="stack.html#class_segmented_stack"> <code class="computeroutput">segmented_stack</code></a> is
the only available stack allocator.
</p></td></tr>
</table></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2013 Oliver Kowalke<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
</div></td>
</tr></table>
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