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<title>Scheduling</title>
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<link rel="home" href="../index.html" title="Chapter 1. Fiber">
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="fiber.scheduling"></a><a class="link" href="scheduling.html" title="Scheduling">Scheduling</a>
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</h2></div></div></div>
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<p>
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Fibers are managed by a scheduler which coordinates the sequence of fibers
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running or waiting. Each thread is required to have its own scheduler. By default,
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<span class="bold"><strong>Boost.Fiber</strong></span> allocates for each thread a scheduler
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( <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
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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
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any other <span class="bold"><strong>Boost.Fiber</strong></span> entry point.
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</p>
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<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">thread_fn</span><span class="special">()</span>
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<span class="special">{</span>
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<span class="identifier">my_fiber_scheduler</span> <span class="identifier">mfs</span><span class="special">;</span>
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<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">&</span> <span class="identifier">mfs</span><span class="special">);</span>
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<span class="special">...</span>
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<span class="special">}</span>
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</pre>
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<p>
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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
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<a class="link" href="../"> <code class="computeroutput">round_robin_ws</code></a>.
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</p>
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<p>
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You are explicitly permitted to code your own <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a> subclass,
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and to pass it to <a class="link" href="fiber_mgmt/fiber.html#set_scheduling_algorithm"> <code class="computeroutput">set_scheduling_algorithm()</code></a>.
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</p>
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<p>
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</p>
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<h5>
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<a name="class_algorithm_bridgehead"></a>
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<span><a name="class_algorithm"></a></span>
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<a class="link" href="scheduling.html#class_algorithm">Class <code class="computeroutput">algorithm</code></a>
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</h5>
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<p>
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</p>
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<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</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">></span>
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<span class="keyword">struct</span> <span class="identifier">sched_algorithm</span>
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<span class="special">{</span>
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<span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">sched_algorithm</span><span class="special">()</span> <span class="special">{}</span>
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<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">awakened</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">worker_fiber</span> <span class="special">*)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
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<span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">worker_fiber</span> <span class="special">*</span> <span class="identifier">pick_next</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
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<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">worker_fiber</span> <span class="special">*,</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>
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<span class="special">};</span>
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<span class="keyword">void</span> <span class="identifier">set_scheduling_algorithm</span><span class="special">(</span> <span class="identifier">sched_algorithm</span> <span class="special">*);</span>
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</pre>
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<p>
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</p>
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<h5>
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<a name="algorithm_awakened_bridgehead"></a>
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<span><a name="algorithm_awakened"></a></span>
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<a class="link" href="scheduling.html#algorithm_awakened">Member function
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<code class="computeroutput">awakened</code>()</a>
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</h5>
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<p>
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</p>
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<pre class="programlisting"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">awakened</span><span class="special">(</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">worker_fiber</span> <span class="special">*</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
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</pre>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl>
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<dt><span class="term">Effects:</span></dt>
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<dd><p>
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Marks fiber <code class="computeroutput"><span class="identifier">f</span></code>, to be
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ready to run.
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</p></dd>
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</dl>
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</div>
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<p>
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</p>
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<h5>
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<a name="algorithm_pick_next_bridgehead"></a>
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<span><a name="algorithm_pick_next"></a></span>
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<a class="link" href="scheduling.html#algorithm_pick_next">Member
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function <code class="computeroutput">pick_next</code>()</a>
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</h5>
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<p>
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</p>
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<pre class="programlisting"><span class="keyword">virtual</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">worker_fiber</span> <span class="special">*</span> <span class="identifier">pick_next</span><span class="special">()</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
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</pre>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl>
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<dt><span class="term">Effects:</span></dt>
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<dd><p>
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Depending on the scheduling algorithm, this function returns the fiber
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which has to be resumed next.
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</p></dd>
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</dl>
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</div>
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<p>
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</p>
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<h5>
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<a name="algorithm_priority_bridgehead"></a>
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<span><a name="algorithm_priority"></a></span>
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<a class="link" href="scheduling.html#algorithm_priority">Member function
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<code class="computeroutput">priority</code>()</a>
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</h5>
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<p>
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</p>
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<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">worker_fiber</span> <span class="special">*,</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>
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</pre>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl>
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<dt><span class="term">Effects:</span></dt>
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<dd><p>
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Reschedule the fiber depending on the priority.
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</p></dd>
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</dl>
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</div>
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<p>
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</p>
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<h5>
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<a name="class_round_robin_bridgehead"></a>
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<span><a name="class_round_robin"></a></span>
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<a class="link" href="scheduling.html#class_round_robin">Class <code class="computeroutput">round_robin</code></a>
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</h5>
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<p>
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</p>
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<p>
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This class implements <a class="link" href="scheduling.html#class_algorithm"> <code class="computeroutput">algorithm</code></a> and schedules fibers in round-robin
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fashion.
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</p>
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<p>
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[info The exsample section provides an scheduler used for migrating fibers
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(work-stealing) between threads (different schedulers).]
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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</div></td>
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</tr></table>
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<hr>
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