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<title>Scheduling</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fiber.scheduling"></a><a class="link" href="scheduling.html" title="Scheduling">Scheduling</a>
</h2></div></div></div>
<p>
Fibers are managed by a scheduler which coordinates the sequence of fibers
running or waiting. Each thread is required to have its own scheduler. By default,
<span class="bold"><strong>Boost.Fiber</strong></span> allocates for each thread a scheduler
( <a class="link" href="scheduling.html#class_round_robin"> <code class="computeroutput">round_robin</code></a>) on the heap. To prevent the library from heap-allocating
a default scheduler for a given thread, that thread must call <a class="link" href="fiber_mgmt/fiber.html#set_scheduling_algorithm"> <code class="computeroutput">set_scheduling_algorithm()</code></a> before
any other <span class="bold"><strong>Boost.Fiber</strong></span> entry point.
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">thread_fn</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">my_fiber_scheduler</span> <span class="identifier">mfs</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">set_scheduling_algorithm</span><span class="special">(</span> <span class="special">&amp;</span> <span class="identifier">mfs</span><span class="special">);</span>
<span class="special">...</span>
<span class="special">}</span>
</pre>
<p>
A fiber-scheduler must implement interface <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a>. <span class="bold"><strong>Boost.Fiber</strong></span> provides two schedulers: <a class="link" href="scheduling.html#class_round_robin"> <code class="computeroutput">round_robin</code></a> and
<a class="link" href="scheduling.html#class_round_robin_ws"> <code class="computeroutput">round_robin_ws</code></a>.
</p>
<p>
You are explicitly permitted to code your own <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a> subclass,
and to pass it to <a class="link" href="fiber_mgmt/fiber.html#set_scheduling_algorithm"> <code class="computeroutput">set_scheduling_algorithm()</code></a>.
</p>
<p>
</p>
<h5>
<a name="class_algorithm_bridgehead"></a>
<span><a name="class_algorithm"></a></span>
<a class="link" href="scheduling.html#class_algorithm">Class <code class="computeroutput">algorithm</code></a>
</h5>
<p>
</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">algorithm</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">algorithm</span>
<span class="special">{</span>
<span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">algorithm</span><span class="special">()</span> <span class="special">{}</span>
<span class="identifier">algorithm</span><span class="special">(</span> <span class="identifier">algorithm</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
<span class="identifier">algorithm</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">algorithm</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">spawn</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">priority</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;,</span> <span class="keyword">int</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">join</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="identifier">active</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">bool</span> <span class="identifier">run</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> <span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> <span class="identifier">clock_type</span><span class="special">::</span><span class="identifier">time_point</span> <span class="keyword">const</span><span class="special">&amp;,</span>
<span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> <span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;,</span>
<span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;);</span>
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">yield</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">id</span> <span class="identifier">get_main_id</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">notify</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="identifier">get_main_notifier</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">void</span> <span class="identifier">set_scheduling_algorithm</span><span class="special">(</span> <span class="identifier">algorithm</span> <span class="special">*);</span>
</pre>
<p>
</p>
<h5>
<a name="algorithm_spawn_bridgehead"></a>
<span><a name="algorithm_spawn"></a></span>
<a class="link" href="scheduling.html#algorithm_spawn">Member function <code class="computeroutput">spawn</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">spawn</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Spawns fiber <code class="computeroutput"><span class="identifier">f</span></code>, e.g.
<code class="computeroutput"><span class="identifier">f</span></code> will be entered the
first time or resumed where it was suspended before. Suspends the current
fiber.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_priority_bridgehead"></a>
<span><a name="algorithm_priority"></a></span>
<a class="link" href="scheduling.html#algorithm_priority">Member function
<code class="computeroutput">priority</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">priority</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">p</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Sets priority <code class="computeroutput"><span class="identifier">p</span></code> for fiber
<code class="computeroutput"><span class="identifier">f</span></code>. Interpretation of
"priority" is entirely up to the subclass.
</p></dd>
<dt><span class="term">Throws:</span></dt>
<dd><p>
Nothing
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_join_bridgehead"></a>
<span><a name="algorithm_join"></a></span>
<a class="link" href="scheduling.html#algorithm_join">Member function <code class="computeroutput">join</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">join</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Suspends the current fiber until fiber <code class="computeroutput"><span class="identifier">f</span></code>
terminates.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_active_bridgehead"></a>
<span><a name="algorithm_active"></a></span>
<a class="link" href="scheduling.html#algorithm_active">Member function
<code class="computeroutput">active</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="identifier">active</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Returns:</span></dt>
<dd><p>
The active fiber, or a null-pointer if the current execution context
is not a fiber managed by this <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a> instance.
</p></dd>
<dt><span class="term">Note:</span></dt>
<dd><p>
While the initial context for a given thread is conceptually also a fiber,
it has no associated <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span></code>
instance. This is when <code class="computeroutput"><span class="identifier">active</span><span class="special">()</span></code> returns null. Higher-level <span class="bold"><strong>Boost.Fiber</strong></span> operations treat a thread's initial
context as equivalent to an explicitly-launched fiber, but this method
operates below that level of abstraction.
</p></dd>
<dt><span class="term">See also:</span></dt>
<dd><p>
<a class="link" href="scheduling.html#algorithm_get_main_id"> <code class="computeroutput">algorithm::get_main_id()</code></a>
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_run_bridgehead"></a>
<span><a name="algorithm_run"></a></span>
<a class="link" href="scheduling.html#algorithm_run">Member function <code class="computeroutput">run</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">bool</span> <span class="identifier">run</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Selects one fiber in ready state and runs it until it suspends. The choice
of fiber is up to the subclass instance.
</p></dd>
<dt><span class="term">Returns:</span></dt>
<dd><p>
Returns <code class="computeroutput"><span class="keyword">true</span></code> if one fiber
was ready and successfully executed, <code class="computeroutput"><span class="keyword">false</span></code>
otherwise.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_wait_bridgehead"></a>
<span><a name="algorithm_wait"></a></span>
<a class="link" href="scheduling.html#algorithm_wait">Member function <code class="computeroutput">wait</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">wait</span><span class="special">(</span> <span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">lk</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Precondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is locked by the current
fiber. It locks the spinlock protecting the internal state of a mutex
or condition_variable.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Current fiber is set to waiting-state and gets suspended.
</p></dd>
<dt><span class="term">Postcondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is unlocked.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_wait_until_bridgehead"></a>
<span><a name="algorithm_wait_until"></a></span>
<a class="link" href="scheduling.html#algorithm_wait_until">Member
function <code class="computeroutput">wait_until</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">bool</span> <span class="identifier">wait_until</span><span class="special">(</span> <span class="identifier">clock_type</span><span class="special">::</span><span class="identifier">time_point</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">timeout_time</span><span class="special">,</span>
<span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">lk</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Precondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is locked by the current
fiber. It locks the spinlock protecting the internal state of a mutex
or condition_variable.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Current fiber is set to waiting-state and gets suspended.
</p></dd>
<dt><span class="term">Returns:</span></dt>
<dd><p>
Returns <code class="computeroutput"><span class="keyword">true</span></code> if fiber was
resumed before time-point <code class="computeroutput"><span class="identifier">timeout_time</span></code>
was reached, <code class="computeroutput"><span class="keyword">false</span></code> otherwise.
</p></dd>
<dt><span class="term">Postcondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is unlocked.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_wait_for_bridgehead"></a>
<span><a name="algorithm_wait_for"></a></span>
<a class="link" href="scheduling.html#algorithm_wait_for">Member function
<code class="computeroutput">wait_for</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Period</span> <span class="special">&gt;</span>
<span class="keyword">bool</span> <span class="identifier">wait_for</span><span class="special">(</span> <span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special">&lt;</span> <span class="identifier">Rep</span><span class="special">,</span> <span class="identifier">Period</span> <span class="special">&gt;</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">timeout_duration</span><span class="special">,</span>
<span class="identifier">unique_lock</span><span class="special">&lt;</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">spinlock</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">lk</span><span class="special">)</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Precondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is locked by the current
fiber. It locks the spinlock protecting the internal state of a mutex
or condition_variable.
</p></dd>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Current fiber is set to waiting-state and gets suspended.
</p></dd>
<dt><span class="term">Returns:</span></dt>
<dd><p>
Returns <code class="computeroutput"><span class="keyword">true</span></code> if fiber was
resumed before time-duration <code class="computeroutput"><span class="identifier">timeout_duration</span></code>
has passed, <code class="computeroutput"><span class="keyword">false</span></code> otherwise.
</p></dd>
<dt><span class="term">Postcondition:</span></dt>
<dd><p>
<code class="computeroutput"><span class="identifier">lk</span></code> is unlocked.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_yield_bridgehead"></a>
<span><a name="algorithm_yield"></a></span>
<a class="link" href="scheduling.html#algorithm_yield">Member function <code class="computeroutput">yield</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">yield</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Effects:</span></dt>
<dd><p>
Suspends active fiber without waiting; that is, the current fiber is
immediately set to ready-state.
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_get_main_id_bridgehead"></a>
<span><a name="algorithm_get_main_id"></a></span>
<a class="link" href="scheduling.html#algorithm_get_main_id">Member
function <code class="computeroutput">get_main_id</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">id</span> <span class="identifier">get_main_id</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Returns:</span></dt>
<dd><p>
A <code class="computeroutput"><span class="identifier">fiber_base</span><span class="special">::</span><span class="identifier">id</span></code> associated with the initial context
of the thread on which the scheduler is running.
</p></dd>
<dt><span class="term">Note:</span></dt>
<dd><p>
While the initial context for a given thread is conceptually also a fiber,
it has no associated <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span></code>
instance. Higher-level <span class="bold"><strong>Boost.Fiber</strong></span> operations
treat a thread's initial context as equivalent to an explicitly-launched
fiber, but this method operates below that level of abstraction.
</p></dd>
<dt><span class="term">See also:</span></dt>
<dd><p>
<a class="link" href="scheduling.html#algorithm_active"> <code class="computeroutput">algorithm::active()</code></a>
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="algorithm_get_main_notifier_bridgehead"></a>
<span><a name="algorithm_get_main_notifier"></a></span>
<a class="link" href="scheduling.html#algorithm_get_main_notifier">Member
function <code class="computeroutput">get_main_notifier</code>()</a>
</h5>
<p>
</p>
<pre class="programlisting"><span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">notify</span><span class="special">::</span><span class="identifier">ptr_t</span> <span class="identifier">get_main_notifier</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
</pre>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">Returns:</span></dt>
<dd><p>
A <code class="computeroutput"><span class="identifier">notify</span><span class="special">::</span><span class="identifier">ptr_t</span></code> associated with the initial context
of the thread on which the scheduler is running.
</p></dd>
<dt><span class="term">Note:</span></dt>
<dd><p>
While the initial context for a given thread is conceptually also a fiber,
it has no associated <code class="computeroutput"><span class="identifier">detail</span><span class="special">::</span><span class="identifier">fiber_base</span></code>
instance. Higher-level <span class="bold"><strong>Boost.Fiber</strong></span> operations
treat a thread's initial context as equivalent to an explicitly-launched
fiber, but this method operates below that level of abstraction. The
<code class="computeroutput"><span class="identifier">notify</span><span class="special">::</span><span class="identifier">ptr_t</span></code> is used in condition_variable
and mutex to signal threads initial context.
</p></dd>
<dt><span class="term">See also:</span></dt>
<dd><p>
<a class="link" href="scheduling.html#algorithm_active"> <code class="computeroutput">algorithm::active()</code></a>
</p></dd>
</dl>
</div>
<p>
</p>
<h5>
<a name="class_round_robin_bridgehead"></a>
<span><a name="class_round_robin"></a></span>
<a class="link" href="scheduling.html#class_round_robin">Class <code class="computeroutput">round_robin</code></a>
</h5>
<p>
</p>
<p>
This class implements <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a> and schedules fibers in round-robin
fashion.
</p>
<p>
</p>
<h5>
<a name="class_round_robin_ws_bridgehead"></a>
<span><a name="class_round_robin_ws"></a></span>
<a class="link" href="scheduling.html#class_round_robin_ws">Class
<code class="computeroutput">round_robin_ws</code></a>
</h5>
<p>
</p>
<p>
<code class="computeroutput"><span class="identifier">round_robin_ws</span></code> is intended
to be used for migrating fibers between threads (different schedulers). For
this purpose the class has two additional functions - <code class="computeroutput"><span class="identifier">steal_from</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">migrate_to</span><span class="special">()</span></code>. This functionality can be used to implement
work-stealing/-sharing in a threadpool.
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">round_robin_ws</span> <span class="identifier">rr</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">set_scheduling_algorithm</span><span class="special">(</span> <span class="special">&amp;</span> <span class="identifier">rr</span><span class="special">);</span>
<span class="comment">// steal a fiber from a scheduler `other_rr` running in another thread</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">fiber</span> <span class="identifier">f</span><span class="special">(</span> <span class="identifier">other_rr</span><span class="special">-&gt;</span><span class="identifier">steal_from</span><span class="special">()</span> <span class="special">);</span>
<span class="comment">// check if stealing was successful</span>
<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">f</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// migrate stolen fiber to scheduler running in this thread</span>
<span class="identifier">rr</span><span class="special">.</span><span class="identifier">migrate_to</span><span class="special">(</span> <span class="identifier">f</span><span class="special">);</span>
<span class="comment">// detach fiber</span>
<span class="identifier">f</span><span class="special">.</span><span class="identifier">detach</span><span class="special">();</span>
<span class="special">}</span>
</pre>
</div>
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<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>
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