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<link rel="home" href="../index.html" title="Chapter 1. Fiber">
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<table cellpadding="2" width="100%"><tr>
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<a accesskey="p" href="performance.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="custom.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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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.rational"></a><a class="link" href="rational.html" title="Rational">Rational</a>
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</h2></div></div></div>
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<h4>
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<a name="fiber.rational.h0"></a>
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<span><a name="fiber.rational.distinction_between_coroutines_and_fibers"></a></span><a class="link" href="rational.html#fiber.rational.distinction_between_coroutines_and_fibers">distinction
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between coroutines and fibers</a>
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</h4>
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<p>
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The fiber library extends the coroutine library by adding a scheduler and synchronization
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mechanisms.
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</p>
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<pre class="programlisting"><span class="special">*</span> <span class="identifier">a</span> <span class="identifier">coroutine</span> <span class="identifier">yields</span>
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<span class="special">*</span> <span class="identifier">a</span> <span class="identifier">fiber</span> <span class="identifier">blocks</span>
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</pre>
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<p>
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When a coroutine yields, it passes control directly to its caller (or, in the
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case of symmetric coroutines, a designated other coroutine). When a fiber blocks,
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it implicitly passes control to the fiber scheduler. Coroutines have no scheduler
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because they need no scheduler. <sup>[<a name="fiber.rational.f0" href="#ftn.fiber.rational.f0" class="footnote">2</a>]</sup>.
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</p>
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<h4>
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<a name="fiber.rational.h1"></a>
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<span><a name="fiber.rational.what_about_transactional_memory"></a></span><a class="link" href="rational.html#fiber.rational.what_about_transactional_memory">what
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about transactional memory</a>
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</h4>
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<p>
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GCC support transactional memory since version 4.7. Unfortunately testes showed
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that transactional memory is slower (ca. 4x) than using spinlocks using atomics.
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If transactional memory will be improved (supporting hybrid tm), spinlocks
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will be replaced by __transaction_atomic{} statements surrounding the critical
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sections.
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</p>
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<h4>
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<a name="fiber.rational.h2"></a>
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<span><a name="fiber.rational.synchronization_between_fibers_running_in_different_threads"></a></span><a class="link" href="rational.html#fiber.rational.synchronization_between_fibers_running_in_different_threads">synchronization
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between fibers running in different threads</a>
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</h4>
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<p>
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Synchronization classes from <a href="../../../../../libs/thread/index.html" target="_top">Boost.Thread</a>
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do block the entire thread. In contrast to this the synchronization classes
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from <span class="bold"><strong>Boost.Fiber</strong></span> do block only the fiber,
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so that the thread is able to schedule and run other fibers in the meantime.
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The synchronization classes from <span class="bold"><strong>Boost.Fiber</strong></span>
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are designed to be thread-safe, e.g. it is possible to synchronize fibers running
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in different schedulers (different threads) or running in the same scheduler
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(same thread). (However, there is a build option to disable that support; see
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<a class="link" href="overview.html#cross_thread_sync">this description</a>.)
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</p>
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<h4>
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<a name="fiber.rational.h3"></a>
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<span><a name="fiber.rational.support_for_boost_asio"></a></span><a class="link" href="rational.html#fiber.rational.support_for_boost_asio">support
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for Boost.Asio</a>
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</h4>
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<p>
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The support for Boost.Asio's <span class="emphasis"><em>async-result</em></span> is not part
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of the official API (implementation provided in example section). <span class="emphasis"><em>async-result</em></span>
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does not reflect that <span class="bold"><strong>Boost.Fiber</strong></span> itself uses
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an internal scheduler (especially fibers not in touch with code using <a href="../../../../../libs/asio/index.html" target="_top">Boost.Asio</a>, for instance a sleeping
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fiber will not be launched explicitly by <a href="../../../../../libs/asio/index.html" target="_top">Boost.Asio</a>).
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The integration of <span class="bold"><strong>Boost.Fiber</strong></span> into <a href="../../../../../libs/asio/index.html" target="_top">Boost.Asio</a> requires some investigation
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from both authors.
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</p>
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<h4>
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<a name="fiber.rational.h4"></a>
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<span><a name="fiber.rational.tested_compilers"></a></span><a class="link" href="rational.html#fiber.rational.tested_compilers">tested
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compilers</a>
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</h4>
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<p>
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The library was tested with GCC-5.1.1, Clang-3.6.0 and MSVC-14.0 in c++14-mode.
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</p>
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<h4>
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<a name="fiber.rational.h5"></a>
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<span><a name="fiber.rational.supported_architectures"></a></span><a class="link" href="rational.html#fiber.rational.supported_architectures">supported
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architectures</a>
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</h4>
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<p>
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<span class="bold"><strong>Boost.Fiber</strong></span> depends on <a href="../../../../../libs/context/index.html" target="_top">Boost.Context</a>
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- the list of supported architectures can be found <a href="../../../../../libs/context/doc/html/context/architectures.html" target="_top">here</a>.
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</p>
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<h4>
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<a name="fiber.rational.h6"></a>
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<span><a name="fiber.rational.migrating_fibers_between_threads"></a></span><a class="link" href="rational.html#fiber.rational.migrating_fibers_between_threads">migrating
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fibers between threads</a>
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</h4>
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<p>
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The support for migrating fibers between threads was removed. Especially in
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the case of NUMA-architectures it is not always advised to migrate data between
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threads. Suppose fiber <span class="emphasis"><em>f</em></span> is running on logical CPU <span class="emphasis"><em>cpu0</em></span>
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which belongs to NUMA node <span class="emphasis"><em>node0</em></span>. The data of <span class="emphasis"><em>f</em></span>
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are allocated on the physical memory located at <span class="emphasis"><em>node0</em></span>.
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Migrating the fiber from <span class="emphasis"><em>cpu0</em></span> to another logical CPU
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<span class="emphasis"><em>cpuX</em></span> which is part of NUMA node <span class="emphasis"><em>nodeX</em></span>
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will reduce the performance of the application because of increased latency
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of memory access.
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</p>
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<div class="footnotes">
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<br><hr width="100" align="left">
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<div class="footnote"><p><sup>[<a name="ftn.fiber.rational.f0" href="#fiber.rational.f0" class="para">2</a>] </sup>
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4024.pdf" target="_top">'N4024:
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Distinguishing coroutines and fibers'</a>
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</p></div>
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</div>
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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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