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|
<html>
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<title>Emulations</title>
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</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="thread.emulations"></a><a class="link" href="emulations.html" title="Emulations">Emulations</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="emulations.html#thread.emulations.delete"><code class="computeroutput"><span class="special">=</span><span class="keyword">delete</span></code> emulation</a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move">Move semantics</a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.bool_explicit_conversion">Bool explicit
conversion</a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.scoped_enums">Scoped Enums</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="thread.emulations.delete"></a><a class="link" href="emulations.html#thread.emulations.delete" title="=delete emulation"><code class="computeroutput"><span class="special">=</span><span class="keyword">delete</span></code> emulation</a>
</h3></div></div></div>
<p>
C++11 allows to delete some implicitly generated functions as constructors
and assignment using '= delete' as in
</p>
<pre class="programlisting"><span class="keyword">public</span><span class="special">:</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">thread</span> <span class="keyword">const</span><span class="special">&)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
</pre>
<p>
On compilers not supporting this feature, Boost.Thread relays on a partial
simulation, it declares the function as private without definition.
</p>
<pre class="programlisting"><span class="keyword">private</span><span class="special">:</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">thread</span> <span class="special">&);</span>
</pre>
<p>
The emulation is partial as the private function can be used for overload
resolution for some compilers and prefer it to other overloads that need
a conversion. See below the consequences on the move semantic emulation.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="thread.emulations.move"></a><a class="link" href="emulations.html#thread.emulations.move" title="Move semantics">Move semantics</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="emulations.html#thread.emulations.move.deprecated">Deprecated Version
2 interface</a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable">Portable interface</a></span></dt>
</dl></div>
<p>
In order to implement Movable classes, move parameters and return types Boost.Thread
uses the rvalue reference when the compiler support it. On compilers not
supporting it Boost.Thread uses either the emulation provided by Boost.Move
or the emulation provided by the previous versions of Boost.Thread depending
whether <code class="computeroutput"><span class="identifier">BOOST_THREAD_USES_MOVE</span></code>
is defined or not. This macros is unset by default when <code class="computeroutput"><span class="identifier">BOOST_THREAD_VERSION</span></code>
is 2. Since <code class="computeroutput"><span class="identifier">BOOST_THREAD_VERSION</span></code>
3, <code class="computeroutput"><span class="identifier">BOOST_THREAD_USES_MOVE</span></code>
is defined.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="thread.emulations.move.deprecated"></a><a class="link" href="emulations.html#thread.emulations.move.deprecated" title="Deprecated Version 2 interface">Deprecated Version
2 interface</a>
</h4></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="emulations.html#thread.emulations.move.deprecated.Helper">Helpers
class and function</a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.deprecated.movable">Movable
emulation</a></span></dt>
</dl></div>
<p>
Previous to version 1.50, Boost.Thread make use of its own move semantic
emulation which had more limitations than the provided by Boost.Move. In
addition, it is of interest of the whole Boost community that Boost.Thread
uses Boost.Move so that boost::thread can be stored on Movable aware containers.
</p>
<p>
To preserve backward compatibility at least during some releases, Boost.Thread
allows the user to use the deprecated move semantic emulation defining
BOOST_THREAD_DONT_USE_MOVE.
</p>
<p>
Many aspects of move semantics can be emulated for compilers not supporting
rvalue references and Boost.Thread legacy offers tools for that purpose.
</p>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.deprecated.Helper"></a><a class="link" href="emulations.html#thread.emulations.move.deprecated.Helper" title="Helpers class and function">Helpers
class and function</a>
</h5></div></div></div>
<p>
Next follows the interface of the legacy move semantic helper class and
function.
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
<span class="special">{</span>
<span class="keyword">namespace</span> <span class="identifier">detail</span>
<span class="special">{</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">thread_move_t</span>
<span class="special">{</span>
<span class="keyword">explicit</span> <span class="identifier">thread_move_t</span><span class="special">(</span><span class="identifier">T</span><span class="special">&</span> <span class="identifier">t_</span><span class="special">);</span>
<span class="identifier">T</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="identifier">T</span><span class="special">*</span> <span class="keyword">operator</span><span class="special">->()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">thread_move_t</span><span class="special">&);</span>
<span class="special">};</span>
<span class="special">}</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">move</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">t</span><span class="special">);</span>
<span class="special">}</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.deprecated.movable"></a><a class="link" href="emulations.html#thread.emulations.move.deprecated.movable" title="Movable emulation">Movable
emulation</a>
</h5></div></div></div>
<p>
We can write a MovableOny class as follows. You just need to follow these
simple steps:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Add a conversion to the <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">classname</span><span class="special">></span></code>
</li>
<li class="listitem">
Make the copy constructor private.
</li>
<li class="listitem">
Write a constructor taking the parameter as <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">classname</span><span class="special">></span></code>
</li>
<li class="listitem">
Write an assignment taking the parameter as <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">classname</span><span class="special">></span></code>
</li>
</ul></div>
<p>
For example the thread class defines the following:
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">thread</span>
<span class="special">{</span>
<span class="comment">// ...</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">thread</span><span class="special">&);</span>
<span class="identifier">thread</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">thread</span><span class="special">&);</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span> <span class="identifier">move</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span> <span class="identifier">x</span><span class="special">(*</span><span class="keyword">this</span><span class="special">);</span>
<span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">operator</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">thread</span><span class="special">>()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">move</span><span class="special">();</span>
<span class="special">}</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span> <span class="identifier">x</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">thread_info</span><span class="special">=</span><span class="identifier">x</span><span class="special">-></span><span class="identifier">thread_info</span><span class="special">;</span>
<span class="identifier">x</span><span class="special">-></span><span class="identifier">thread_info</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span>
<span class="special">}</span>
<span class="identifier">thread</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">thread_move_t</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span> <span class="identifier">x</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">thread</span> <span class="identifier">new_thread</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
<span class="identifier">swap</span><span class="special">(</span><span class="identifier">new_thread</span><span class="special">);</span>
<span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span>
<span class="special">}</span>
<span class="comment">// ...</span>
<span class="special">};</span>
</pre>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="thread.emulations.move.portable"></a><a class="link" href="emulations.html#thread.emulations.move.portable" title="Portable interface">Portable interface</a>
</h4></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.NO_COPYABLE"><code class="computeroutput"><span class="identifier">BOOST_THREAD_NO_COPYABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.MOVABLE"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.MOVABLE_ONLY"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE_ONLY</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.COPYABLE_AND_MOVABLE"><code class="computeroutput"><span class="identifier">BOOST_THREAD_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.RV_REF"><code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>,
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_BEG</span></code>
and <code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_END</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.RV"><code class="computeroutput"><span class="identifier">BOOST_THREAD_RV</span><span class="special">(</span><span class="identifier">V</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.MAKE_RV_REF"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MAKE_RV_REF</span><span class="special">(</span><span class="identifier">RVALUE</span><span class="special">)</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.move.portable.DCL_MOVABLE"><code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span></code>, <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_BEG</span><span class="special">(</span><span class="identifier">T1</span><span class="special">)</span></code> and
<code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_END</span></code></a></span></dt>
</dl></div>
<p>
In order to make the library code portable Boost.Thread uses some macros
that will use either the ones provided by Boost.Move or the deprecated
move semantics provided by previous versions of Boost.Thread.
</p>
<p>
See the Boost.Move documentation for a complete description on how to declare
new Movable classes and its limitations.
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code> is the equivalent of <code class="computeroutput"><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_BEG</span></code>
is the equivalent of <code class="computeroutput"><span class="identifier">BOOST_RV_REF_BEG</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_END</span></code>
is the equivalent of <code class="computeroutput"><span class="identifier">BOOST_RV_REF_END</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_FWD_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code> is the equivalent of `BOOST_FWD_REF(TYPE)
</li>
</ul></div>
<p>
In addition the following macros are needed to make the code portable:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV</span><span class="special">(</span><span class="identifier">V</span><span class="special">)</span></code>
macro to access the rvalue from a BOOST_THREAD_RV_REF(TYPE),
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_MAKE_RV_REF</span><span class="special">(</span><span class="identifier">RVALUE</span><span class="special">)</span></code> makes a rvalue.
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code> to avoid conflicts with Boost.Move
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_BEG</span><span class="special">(</span><span class="identifier">T1</span><span class="special">)</span></code> and <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_END</span></code>
are variant of <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span></code>
when the parameter is a template instantiation.
</li>
</ul></div>
<p>
Other macros are provided and must be included on the public section:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_NO_COPYABLE</span></code>
declares a class no-copyable either deleting the copy constructors
and copy assignment or moving them to the private section.
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code> declares all the implicit conversions
to an rvalue-reference.
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE_ONLY</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code> is the equivalent of <code class="computeroutput"><span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">BOOST_THREAD_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code> is the equivalent of <code class="computeroutput"><span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code>
</li>
</ul></div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.NO_COPYABLE"></a><a class="link" href="emulations.html#thread.emulations.move.portable.NO_COPYABLE" title="BOOST_THREAD_NO_COPYABLE(CLASS)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_NO_COPYABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
This macro marks a class as no copyable, disabling copy construction
and assignment.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.MOVABLE"></a><a class="link" href="emulations.html#thread.emulations.move.portable.MOVABLE" title="BOOST_THREAD_MOVABLE(CLASS)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
This macro marks a class as movable, declaring all the implicit conversions
to an rvalue-reference.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.MOVABLE_ONLY"></a><a class="link" href="emulations.html#thread.emulations.move.portable.MOVABLE_ONLY" title="BOOST_THREAD_MOVABLE_ONLY(CLASS)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE_ONLY</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
This macro marks a type as movable but not copyable, disabling copy construction
and assignment. The user will need to write a move constructor/assignment
to fully write a movable but not copyable class.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.COPYABLE_AND_MOVABLE"></a><a class="link" href="emulations.html#thread.emulations.move.portable.COPYABLE_AND_MOVABLE" title="BOOST_THREAD_COPYABLE_AND_MOVABLE(CLASS)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
This macro marks a type as copyable and movable. The user will need to
write a move constructor/assignment and a copy assignment to fully write
a copyable and movable class.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.RV_REF"></a><a class="link" href="emulations.html#thread.emulations.move.portable.RV_REF" title="BOOST_THREAD_RV_REF(TYPE), BOOST_THREAD_RV_REF_BEG and BOOST_THREAD_RV_REF_END"><code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>,
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_BEG</span></code>
and <code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_END</span></code></a>
</h5></div></div></div>
<p>
This macro is used to achieve portable syntax in move constructors and
assignments for classes marked as <code class="computeroutput"><span class="identifier">BOOST_THREAD_COPYABLE_AND_MOVABLE</span></code>
or <code class="computeroutput"><span class="identifier">BOOST_THREAD_MOVABLE_ONLY</span></code>.
</p>
<p>
<code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_BEG</span></code>
and <code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF_END</span></code>
are used when the parameter end with a <code class="computeroutput"><span class="special">></span></code>
to avoid the compiler error.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.RV"></a><a class="link" href="emulations.html#thread.emulations.move.portable.RV" title="BOOST_THREAD_RV(V)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_RV</span><span class="special">(</span><span class="identifier">V</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
While Boost.Move emulation allows to access an rvalue reference <code class="computeroutput"><span class="identifier">BOOST_THREAD_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span></code>
using the dot operator, the legacy defines the <code class="computeroutput"><span class="keyword">operator</span><span class="special">-></span></code>. We need then a macro <code class="computeroutput"><span class="identifier">BOOST_THREAD_RV</span></code> that mask this difference.
E.g.
</p>
<pre class="programlisting"><span class="identifier">thread</span><span class="special">(</span><span class="identifier">BOOST_THREAD_RV_REF</span><span class="special">(</span><span class="identifier">thread</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">thread_info</span><span class="special">=</span><span class="identifier">BOOST_THREAD_RV</span><span class="special">(</span><span class="identifier">x</span><span class="special">).</span><span class="identifier">thread_info</span><span class="special">;</span>
<span class="identifier">BOOST_THREAD_RV</span><span class="special">(</span><span class="identifier">x</span><span class="special">).</span><span class="identifier">thread_info</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<p>
The use of this macros has reduced considerably the size of the Boost.Thread
move related code.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.MAKE_RV_REF"></a><a class="link" href="emulations.html#thread.emulations.move.portable.MAKE_RV_REF" title="BOOST_THREAD_MAKE_RV_REF(RVALUE)"><code class="computeroutput"><span class="identifier">BOOST_THREAD_MAKE_RV_REF</span><span class="special">(</span><span class="identifier">RVALUE</span><span class="special">)</span></code></a>
</h5></div></div></div>
<p>
While Boost.Move is the best C++03 move emulation there are some limitations
that impact the way the library can be used. For example, with the following
declarations
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">thread</span> <span class="special">{</span>
<span class="comment">// ...</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">thread</span> <span class="special">&);</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">thread</span><span class="special">(</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">thread</span><span class="special">>&);</span>
<span class="comment">// ...</span>
<span class="special">};</span>
</pre>
<p>
This could not work on some compilers even if thread is convertible to
<code class="computeroutput"><span class="identifier">rv</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span></code>
because the compiler prefers the private copy constructor.
</p>
<pre class="programlisting"><span class="identifier">thread</span> <span class="identifier">mkth</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">thread</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<p>
On these compilers we need to use instead an explicit conversion. The
library provides a move member function that allows to workaround the
issue.
</p>
<pre class="programlisting"><span class="identifier">thread</span> <span class="identifier">mkth</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">thread</span><span class="special">(</span><span class="identifier">f</span><span class="special">).</span><span class="identifier">move</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<p>
Note that <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span></code>
can not be used in this case as thread is not implicitly convertible
to <code class="computeroutput"><span class="identifier">thread</span><span class="special">&</span></code>.
</p>
<pre class="programlisting"><span class="identifier">thread</span> <span class="identifier">mkth</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">thread</span><span class="special">(</span><span class="identifier">f</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p>
To make the code portable Boost.Thread the user needs to use a macro
<code class="computeroutput"><span class="identifier">BOOST_THREAD_MAKE_RV_REF</span></code>
that can be used as in
</p>
<pre class="programlisting"><span class="identifier">thread</span> <span class="identifier">mkth</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">BOOST_THREAD_MAKE_RV_REF</span><span class="special">(</span><span class="identifier">thread</span><span class="special">(</span><span class="identifier">f</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p>
Note that this limitation is shared also by the legacy Boost.Thread move
emulation.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="thread.emulations.move.portable.DCL_MOVABLE"></a><a class="link" href="emulations.html#thread.emulations.move.portable.DCL_MOVABLE" title="BOOST_THREAD_DCL_MOVABLE, BOOST_THREAD_DCL_MOVABLE_BEG(T1) and BOOST_THREAD_DCL_MOVABLE_END"><code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span></code>, <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_BEG</span><span class="special">(</span><span class="identifier">T1</span><span class="special">)</span></code> and
<code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_END</span></code></a>
</h5></div></div></div>
<p>
As Boost.Move defines also the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span></code>
function we need to specialize the <code class="computeroutput"><span class="identifier">has_move_emulation_enabled_aux</span></code>
metafunction.
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><></span>
<span class="keyword">struct</span> <span class="identifier">has_move_emulation_enabled_aux</span><span class="special"><</span><span class="identifier">thread</span><span class="special">></span>
<span class="special">:</span> <span class="identifier">BOOST_MOVE_BOOST_NS</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">bool</span><span class="special">,</span> <span class="keyword">true</span><span class="special">></span>
<span class="special">{};</span>
</pre>
<p>
so that the following Boost.Move overload is disabled
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">BOOST_MOVE_BOOST_NS</span><span class="special">::</span><span class="identifier">disable_if</span><span class="special"><</span><span class="identifier">has_move_emulation_enabled_aux</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">T</span><span class="special">&>::</span><span class="identifier">type</span> <span class="identifier">move</span><span class="special">(</span><span class="identifier">T</span><span class="special">&</span> <span class="identifier">x</span><span class="special">);</span>
</pre>
<p>
The macros <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span><span class="special">(</span><span class="identifier">CLASS</span><span class="special">)</span></code>, <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_BEG</span><span class="special">(</span><span class="identifier">T1</span><span class="special">)</span></code> and <code class="computeroutput"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_END</span></code>
are used for this purpose. E.g.
</p>
<pre class="programlisting"><span class="identifier">BOOST_THREAD_DCL_MOVABLE</span><span class="special">(</span><span class="identifier">thread</span><span class="special">)</span>
</pre>
<p>
and
</p>
<pre class="programlisting"><span class="identifier">BOOST_THREAD_DCL_MOVABLE_BEG</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span> <span class="identifier">promise</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">BOOST_THREAD_DCL_MOVABLE_END</span>
</pre>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="thread.emulations.bool_explicit_conversion"></a><a class="link" href="emulations.html#thread.emulations.bool_explicit_conversion" title="Bool explicit conversion">Bool explicit
conversion</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="emulations.html#thread.emulations.bool_explicit_conversion.bool_conversion"><code class="computeroutput"><span class="keyword">operator</span> </code><span class="emphasis"><em>unspecified-bool-type</em></span><code class="computeroutput"><span class="special">()</span> <span class="keyword">const</span></code></a></span></dt>
<dt><span class="section"><a href="emulations.html#thread.emulations.bool_explicit_conversion.operator_not"><code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span></code></a></span></dt>
</dl></div>
<p>
Locks provide an explicit bool conversion operator when the compiler provides
them.
</p>
<pre class="programlisting"><span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
</pre>
<p>
The library provides un implicit conversion to an undefined type that can
be used as a conditional expression.
</p>
<pre class="programlisting"><span class="preprocessor">#if</span> <span class="identifier">defined</span><span class="special">(</span><span class="identifier">BOOST_NO_EXPLICIT_CONVERSION_OPERATORS</span><span class="special">)</span>
<span class="keyword">operator</span> <span class="emphasis"><em>unspecified-bool-type</em></span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="preprocessor">#else</span>
<span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="preprocessor">#endif</span>
</pre>
<p>
The user should use the lock.owns_lock() when a explicit conversion is required.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="thread.emulations.bool_explicit_conversion.bool_conversion"></a><a class="link" href="emulations.html#thread.emulations.bool_explicit_conversion.bool_conversion" title="operator unspecified-bool-type() const"><code class="computeroutput"><span class="keyword">operator</span> </code><span class="emphasis"><em>unspecified-bool-type</em></span><code class="computeroutput"><span class="special">()</span> <span class="keyword">const</span></code></a>
</h4></div></div></div>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">Returns:</span></dt>
<dd><p>
If <a class="link" href="synchronization.html#thread.synchronization.locks.unique_lock.owns_lock" title="bool owns_lock() const"><code class="computeroutput"><span class="identifier">owns_lock</span><span class="special">()</span></code></a>
would return <code class="computeroutput"><span class="keyword">true</span></code>, a
value that evaluates to <code class="computeroutput"><span class="keyword">true</span></code>
in boolean contexts, otherwise a value that evaluates to <code class="computeroutput"><span class="keyword">false</span></code> in boolean contexts.
</p></dd>
<dt><span class="term">Throws:</span></dt>
<dd><p>
Nothing.
</p></dd>
</dl>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="thread.emulations.bool_explicit_conversion.operator_not"></a><a class="link" href="emulations.html#thread.emulations.bool_explicit_conversion.operator_not" title="bool operator!() const"><code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span></code></a>
</h4></div></div></div>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">Returns:</span></dt>
<dd><p>
<code class="computeroutput"><span class="special">!</span></code> <a class="link" href="synchronization.html#thread.synchronization.locks.unique_lock.owns_lock" title="bool owns_lock() const"><code class="computeroutput"><span class="identifier">owns_lock</span><span class="special">()</span></code></a>.
</p></dd>
<dt><span class="term">Throws:</span></dt>
<dd><p>
Nothing.
</p></dd>
</dl>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="thread.emulations.scoped_enums"></a><a class="link" href="emulations.html#thread.emulations.scoped_enums" title="Scoped Enums">Scoped Enums</a>
</h3></div></div></div>
<p>
Some of the enumerations defined in the standard library are scoped enums.
</p>
<p>
On compilers that don't support them, the library uses a class to wrap the
underlying type. Instead of
</p>
<pre class="programlisting"><span class="keyword">enum</span> <span class="keyword">class</span> <span class="identifier">future_errc</span>
<span class="special">{</span>
<span class="identifier">broken_promise</span><span class="special">,</span>
<span class="identifier">future_already_retrieved</span><span class="special">,</span>
<span class="identifier">promise_already_satisfied</span><span class="special">,</span>
<span class="identifier">no_state</span>
<span class="special">};</span>
</pre>
<p>
the library declare these types as
</p>
<pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_DECLARE_BEGIN</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">broken_promise</span><span class="special">,</span>
<span class="identifier">future_already_retrieved</span><span class="special">,</span>
<span class="identifier">promise_already_satisfied</span><span class="special">,</span>
<span class="identifier">no_state</span>
<span class="special">}</span>
<span class="identifier">BOOST_SCOPED_ENUM_DECLARE_END</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span>
</pre>
<p>
These macros allows to use 'future_errc' in almost all the cases as an scoped
enum.
</p>
<p>
There are however some limitations:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The type is not a C++ enum, so 'is_enum<future_errc>' will be false_type.
</li>
<li class="listitem">
The emulated scoped enum can not be used in switch nor in template arguments.
For these cases the user needs to use some macros.
</li>
</ul></div>
<p>
Instead of
</p>
<pre class="programlisting"> <span class="keyword">switch</span> <span class="special">(</span><span class="identifier">ev</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">case</span> <span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span><span class="special">:</span>
<span class="comment">// ...</span>
</pre>
<p>
use
</p>
<pre class="programlisting"><span class="keyword">switch</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">native_value</span><span class="special">(</span><span class="identifier">ev</span><span class="special">))</span>
<span class="special">{</span>
<span class="keyword">case</span> <span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span><span class="special">:</span>
</pre>
<p>
And instead of
</p>
<pre class="programlisting"><span class="preprocessor">#ifdef</span> <span class="identifier">BOOST_NO_SCOPED_ENUMS</span>
<span class="keyword">template</span> <span class="special"><></span>
<span class="keyword">struct</span> <span class="identifier">BOOST_SYMBOL_VISIBLE</span> <span class="identifier">is_error_code_enum</span><span class="special"><</span><span class="identifier">future_errc</span><span class="special">></span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">true_type</span> <span class="special">{</span> <span class="special">};</span>
<span class="preprocessor">#endif</span>
</pre>
<p>
use
</p>
<pre class="programlisting"><span class="preprocessor">#ifdef</span> <span class="identifier">BOOST_NO_SCOPED_ENUMS</span>
<span class="keyword">template</span> <span class="special"><></span>
<span class="keyword">struct</span> <span class="identifier">BOOST_SYMBOL_VISIBLE</span> <span class="identifier">is_error_code_enum</span><span class="special"><</span><span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">enum_type</span><span class="special">></span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">true_type</span> <span class="special">{</span> <span class="special">};</span>
<span class="preprocessor">#endif</span>
</pre>
</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 © 2007 -11 Anthony Williams<br>Copyright © 2011 -14 Vicente J. Botet Escriba<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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