1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Running with worker threads</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Fiber"> 8<link rel="up" href="../index.html" title="Chapter 1. Fiber"> 9<link rel="prev" href="gpu_computing/hip.html" title="ROCm/HIP"> 10<link rel="next" href="performance.html" title="Performance"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="gpu_computing/hip.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="fiber.worker"></a><a name="worker"></a><a class="link" href="worker.html" title="Running with worker threads">Running with worker 28 threads</a> 29</h2></div></div></div> 30<h4> 31<a name="fiber.worker.h0"></a> 32 <span class="phrase"><a name="fiber.worker.keep_workers_running"></a></span><a class="link" href="worker.html#fiber.worker.keep_workers_running">Keep 33 workers running</a> 34 </h4> 35<p> 36 If a worker thread is used but no fiber is created or parts of the framework 37 (like <a class="link" href="fiber_mgmt/this_fiber.html#this_fiber_yield"><code class="computeroutput">this_fiber::yield()</code></a>) are touched, then no fiber scheduler 38 is instantiated. 39 </p> 40<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">worker</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">thread</span><span class="special">(</span> 41 <span class="special">[]{</span> 42 <span class="comment">// fiber scheduler not instantiated</span> 43 <span class="special">});</span> 44<span class="identifier">worker</span><span class="special">.</span><span class="identifier">join</span><span class="special">();</span> 45</pre> 46<p> 47 If <span class="emphasis"><em>use_scheduling_algorithm<>()</em></span> is invoked, the 48 fiber scheduler is created. If the worker thread simply returns, destroys the 49 scheduler and terminates. 50 </p> 51<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">worker</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">thread</span><span class="special">(</span> 52 <span class="special">[]{</span> 53 <span class="comment">// fiber scheduler created</span> 54 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">use_scheduling_algorithm</span><span class="special"><</span><span class="identifier">my_fiber_scheduler</span><span class="special">>();</span> 55 <span class="special">});</span> 56<span class="identifier">worker</span><span class="special">.</span><span class="identifier">join</span><span class="special">();</span> 57</pre> 58<p> 59 In order to keep the worker thread running, the fiber associated with the thread 60 stack (which is called <span class="quote">“<span class="quote">main</span>”</span> fiber) is blocked. For instance 61 the <span class="quote">“<span class="quote">main</span>”</span> fiber might wait on a <a class="link" href="synchronization/conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a>. 62 For a gracefully shutdown <a class="link" href="synchronization/conditions.html#class_condition_variable"><code class="computeroutput">condition_variable</code></a> is signalled 63 and the <span class="quote">“<span class="quote">main</span>”</span> fiber returns. The scheduler gets destructed if 64 all fibers of the worker thread have been terminated. 65 </p> 66<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="identifier">mtx</span><span class="special">;</span> 67<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">condition_variable_any</span> <span class="identifier">cv</span><span class="special">;</span> 68<span class="keyword">auto</span> <span class="identifier">worker</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">thread</span><span class="special">(</span> 69 <span class="special">[&</span><span class="identifier">mtx</span><span class="special">,&</span><span class="identifier">cv</span><span class="special">]{</span> 70 <span class="identifier">mtx</span><span class="special">.</span><span class="identifier">lock</span><span class="special">();</span> 71 <span class="comment">// suspend till signalled</span> 72 <span class="identifier">cv</span><span class="special">.</span><span class="identifier">wait</span><span class="special">(</span><span class="identifier">mtx</span><span class="special">);</span> 73 <span class="identifier">mtx</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">();</span> 74 <span class="special">});</span> 75<span class="comment">// signal termination</span> 76<span class="identifier">cv</span><span class="special">.</span><span class="identifier">notify_all</span><span class="special">();</span> 77<span class="identifier">worker</span><span class="special">.</span><span class="identifier">join</span><span class="special">();</span> 78</pre> 79<h4> 80<a name="fiber.worker.h1"></a> 81 <span class="phrase"><a name="fiber.worker.processing_tasks"></a></span><a class="link" href="worker.html#fiber.worker.processing_tasks">Processing 82 tasks</a> 83 </h4> 84<p> 85 Tasks can be transferred via channels. The worker thread runs a pool of fibers 86 that dequeue and executed tasks from the channel. The termination is signalled 87 via closing the channel. 88 </p> 89<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">task</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">void</span><span class="special">()>;</span> 90<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">buffered_channel</span><span class="special"><</span><span class="identifier">task</span><span class="special">></span> <span class="identifier">ch</span><span class="special">{</span><span class="number">1024</span><span class="special">};</span> 91<span class="keyword">auto</span> <span class="identifier">worker</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">thread</span><span class="special">(</span> 92 <span class="special">[&</span><span class="identifier">ch</span><span class="special">]{</span> 93 <span class="comment">// create pool of fibers</span> 94 <span class="keyword">for</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">=</span><span class="number">0</span><span class="special">;</span> <span class="identifier">i</span><span class="special"><</span><span class="number">10</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> 95 <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="special">{</span> 96 <span class="special">[&</span><span class="identifier">ch</span><span class="special">]{</span> 97 <span class="identifier">task</span> <span class="identifier">tsk</span><span class="special">;</span> 98 <span class="comment">// dequeue and process tasks</span> 99 <span class="keyword">while</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">channel_op_status</span><span class="special">::</span><span class="identifier">closed</span><span class="special">!=</span><span class="identifier">ch</span><span class="special">.</span><span class="identifier">pop</span><span class="special">(</span><span class="identifier">tsk</span><span class="special">)){</span> 100 <span class="identifier">tsk</span><span class="special">();</span> 101 <span class="special">}</span> 102 <span class="special">}}.</span><span class="identifier">detach</span><span class="special">();</span> 103 <span class="special">}</span> 104 <span class="identifier">task</span> <span class="identifier">tsk</span><span class="special">;</span> 105 <span class="comment">// dequeue and process tasks</span> 106 <span class="keyword">while</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">channel_op_status</span><span class="special">::</span><span class="identifier">closed</span><span class="special">!=</span><span class="identifier">ch</span><span class="special">.</span><span class="identifier">pop</span><span class="special">(</span><span class="identifier">tsk</span><span class="special">)){</span> 107 <span class="identifier">tsk</span><span class="special">();</span> 108 <span class="special">}</span> 109 <span class="special">});</span> 110<span class="comment">// feed channel with tasks</span> 111<span class="identifier">ch</span><span class="special">.</span><span class="identifier">push</span><span class="special">([]{</span> <span class="special">...</span> <span class="special">});</span> 112<span class="special">...</span> 113<span class="comment">// signal termination</span> 114<span class="identifier">ch</span><span class="special">.</span><span class="identifier">close</span><span class="special">();</span> 115<span class="identifier">worker</span><span class="special">.</span><span class="identifier">join</span><span class="special">();</span> 116</pre> 117<p> 118 An alternative is to use a work-stealing scheduler. This kind of scheduling 119 algorithm a worker thread steals fibers from the ready-queue of other worker 120 threads if its own ready-queue is empty. 121 </p> 122<div class="note"><table border="0" summary="Note"> 123<tr> 124<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 125<th align="left">Note</th> 126</tr> 127<tr><td align="left" valign="top"><p> 128 Wait till all worker threads have registered the work-stealing scheduling 129 algorithm. 130 </p></td></tr> 131</table></div> 132<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">mutex</span> <span class="identifier">mtx</span><span class="special">;</span> 133<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">condition_variable_any</span> <span class="identifier">cv</span><span class="special">;</span> 134<span class="comment">// start wotrker-thread first</span> 135<span class="keyword">auto</span> <span class="identifier">worker</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">thread</span><span class="special">(</span> 136 <span class="special">[&</span><span class="identifier">mtx</span><span class="special">,&</span><span class="identifier">cv</span><span class="special">]{</span> 137 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">use_scheduling_algorithm</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">algo</span><span class="special">::</span><span class="identifier">work_stealing</span><span class="special">>(</span><span class="number">2</span><span class="special">);</span> 138 <span class="identifier">mtx</span><span class="special">.</span><span class="identifier">lock</span><span class="special">();</span> 139 <span class="comment">// suspend main-fiber from the worker thread</span> 140 <span class="identifier">cv</span><span class="special">.</span><span class="identifier">wait</span><span class="special">(</span><span class="identifier">mtx</span><span class="special">);</span> 141 <span class="identifier">mtx</span><span class="special">.</span><span class="identifier">unlock</span><span class="special">();</span> 142 <span class="special">});</span> 143<span class="identifier">boost</span><span class="special">::</span><span class="identifier">fibers</span><span class="special">::</span><span class="identifier">use_scheduling_algorithm</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">algo</span><span class="special">::</span><span class="identifier">work_stealing</span><span class="special">>(</span><span class="number">2</span><span class="special">);</span> 144<span class="comment">// create fibers with tasks</span> 145<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="special">...</span> <span class="special">}};</span> 146<span class="special">...</span> 147<span class="comment">// signal termination</span> 148<span class="identifier">cv</span><span class="special">.</span><span class="identifier">notify_all</span><span class="special">();</span> 149<span class="identifier">worker</span><span class="special">.</span><span class="identifier">join</span><span class="special">();</span> 150</pre> 151<div class="important"><table border="0" summary="Important"> 152<tr> 153<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> 154<th align="left">Important</th> 155</tr> 156<tr><td align="left" valign="top"><p> 157 Because the TIB (thread information block on Windows) is not fully described 158 in the MSDN, it might be possible that not all required TIB-parts are swapped. 159 Using WinFiber implementation might be an alternative (see documentation 160 about <a href="http://www.boost.org/doc/libs/1_65_1/libs/context/doc/html/context/cc/implementations__fcontext_t__ucontext_t_and_winfiber.html" target="_top"><span class="emphasis"><em>implementations 161 fcontext_t, ucontext_t and WinFiber of boost.context</em></span></a>). 162 </p></td></tr> 163</table></div> 164</div> 165<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 166<td align="left"></td> 167<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> 168 Distributed under the Boost Software License, Version 1.0. (See accompanying 169 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>) 170 </p> 171</div></td> 172</tr></table> 173<hr> 174<div class="spirit-nav"> 175<a accesskey="p" href="gpu_computing/hip.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 176</div> 177</body> 178</html> 179
