gcc/libstdc++-v3/doc/html/manual/ext_concurrency.html - Issue 3050029: [gcc] GCC 4.5.0=>4.5.1

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Issue 3050029: [gcc] GCC 4.5.0=>4.5.1 (Closed) Base URL: ssh://git@gitrw.chromium.org:9222/nacl-toolchain.git

Patch Set: Created 10 years, 5 months ago

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-<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 40. Concurrency</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content="
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 " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="extensions.html" title="Part XII. Extensions" /><link rel="prev" href="ext_demangling.html" title="Chapter 39. Demangling" /><link rel="next" href="bk01pt12ch40s02.html" title="Implementation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 40. Concurrency</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_demangling.html">Prev</a> </td><th width="60%" align="center">Part XII.

- Extensions

-</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt12ch40s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.concurrency"></a>Chapter 40. Concurrency</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ext_concurrency.html#manual.ext.concurrency.design">Design</a></span></dt><dd><dl><dt><span class="sect2"><a href="ext_concurrency.html#manual.ext.concurrency.design.threads">Interface to Locks and Mutexes</a></span></dt><dt><span class="sect2"><a href="ext_concurrency.html#manual.ext.concurrency.design.atomics">Interface to Atomic Functions</a></span></dt></dl></dd><dt><span class="sect1"><a href="bk01pt12ch40s02.html">Implementation</a></span></dt><dd><dl><dt><span class="sect2"><a href="bk01pt12ch40s02.html#manual.ext.concurrency.impl.atomic_fallbacks">Using Builtin Atomic Functions</a></span></dt><dt><span class="sect2"><a href="bk01pt12ch40s02.html#manual.ext.concurrency.impl.thread">Thread Abstraction</a></span></dt></dl></dd><dt><span class="sect1"><a href="bk01pt12ch40s03.html">Use</a></span></dt></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.concurrency.design"></a>Design</h2></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.concurrency.design.threads"></a>Interface to Locks and Mutexes</h3></div></div></div><p>The file <ext/concurrence.h> contains all the higher-level

-constructs for playing with threads. In contrast to the atomics layer,

-the concurrence layer consists largely of types. All types are defined within <code class="code">namespace __gnu_cxx</code>.

-</p><p>

-These types can be used in a portable manner, regardless of the

-specific environment. They are carefully designed to provide optimum

-efficiency and speed, abstracting out underlying thread calls and

-accesses when compiling for single-threaded situations (even on hosts

-that support multiple threads.)

-</p><p>The enumerated type <code class="code">_Lock_policy</code> details the set of

-available locking

-policies: <code class="code">_S_single</code>, <code class="code">_S_mutex</code>,

-and <code class="code">_S_atomic</code>.

-</p><div class="itemizedlist"><ul type="disc"><li><p><code class="code">_S_single</code></p><p>Indicates single-threaded code that does not need locking.

-</p></li><li><p><code class="code">_S_mutex</code></p><p>Indicates multi-threaded code using thread-layer abstractions.

-</p></li><li><p><code class="code">_S_atomic</code></p><p>Indicates multi-threaded code using atomic operations.

-</p></li></ul></div><p>The compile-time constant <code class="code">__default_lock_policy</code> is set

-to one of the three values above, depending on characteristics of the

-host environment and the current compilation flags.

-</p><p>Two more datatypes make up the rest of the

-interface: <code class="code">__mutex</code>, and <code class="code">__scoped_lock</code>.

-</p><p>

-</p><p>The scoped lock idiom is well-discussed within the C++

-community. This version takes a <code class="code">__mutex</code> reference, and

-locks it during construction of <code class="code">__scoped_locke</code> and

-unlocks it during destruction. This is an efficient way of locking

-critical sections, while retaining exception-safety.

-</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.concurrency.design.atomics"></a>Interface to Atomic Functions</h3></div></div></div><p>

-Two functions and one type form the base of atomic support.

-</p><p>The type <code class="code">_Atomic_word</code> is a signed integral type

-supporting atomic operations.

-</p><p>

-The two functions functions are:

-</p><pre class="programlisting">

-_Atomic_word

-__exchange_and_add_dispatch(volatile _Atomic_word*, int);

-void

-__atomic_add_dispatch(volatile _Atomic_word*, int);

-</pre><p>Both of these functions are declared in the header file

-<ext/atomicity.h>, and are in <code class="code">namespace __gnu_cxx</code>.

-</p><div class="itemizedlist"><ul type="disc"><li><p>

-<code class="code">

-__exchange_and_add_dispatch

-</code>

-</p><p>Adds the second argument's value to the first argument. Returns the old value.

-</p></li><li><p>

-<code class="code">

-__atomic_add_dispatch

-</code>

-</p><p>Adds the second argument's value to the first argument. Has no return value.

-</p></li></ul></div><p>

-These functions forward to one of several specialized helper

-functions, depending on the circumstances. For instance,

-</p><p>

-<code class="code">

-__exchange_and_add_dispatch

-</code>

-</p><p>

-Calls through to either of:

-</p><div class="itemizedlist"><ul type="disc"><li><p><code class="code">__exchange_and_add</code>

-</p><p>Multi-thread version. Inlined if compiler-generated builtin atomics

-can be used, otherwise resolved at link time to a non-builtin code

-sequence.

-</p></li><li><p><code class="code">__exchange_and_add_single</code>

-</p><p>Single threaded version. Inlined.</p></li></ul></div><p>However, only <code class="code">__exchange_and_add_dispatch</code>

-and <code class="code">__atomic_add_dispatch</code> should be used. These functions

-can be used in a portable manner, regardless of the specific

-environment. They are carefully designed to provide optimum efficiency

-and speed, abstracting out atomic accesses when they are not required

-(even on hosts that support compiler intrinsics for atomic

-operations.)

-</p><p>

-In addition, there are two macros

-</p><p>

-<code class="code">

-_GLIBCXX_READ_MEM_BARRIER

-</code>

-</p><p>

-<code class="code">

-_GLIBCXX_WRITE_MEM_BARRIER

-</code>

-</p><p>

-Which expand to the appropriate write and read barrier required by the

-host hardware and operating system.

-</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_demangling.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt12ch40s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 39. Demangling </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Implementation</td></tr></table></div></body></html>

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