mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-30 19:53:46 +00:00
46 lines
5.7 KiB
HTML
46 lines
5.7 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
||
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
|
||
<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Implementation</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" ISO C++ , library "/><meta name="keywords" content=" ISO C++ , library "/><meta name="keywords" content=" ISO C++ , runtime , library "/><link rel="home" href="../index.html" title="The GNU C++ Library"/><link rel="up" href="ext_concurrency.html" title="Chapter 30. Concurrency"/><link rel="prev" href="ext_concurrency.html" title="Chapter 30. Concurrency"/><link rel="next" href="bk01pt03ch30s03.html" title="Use"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Implementation</th></tr><tr><td align="left"><a accesskey="p" href="ext_concurrency.html">Prev</a> </td><th width="60%" align="center">Chapter 30. Concurrency</th><td align="right"> <a accesskey="n" href="bk01pt03ch30s03.html">Next</a></td></tr></table><hr/></div><div class="section" title="Implementation"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.concurrency.impl"/>Implementation</h2></div></div></div><div class="section" title="Using Builtin Atomic Functions"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.concurrency.impl.atomic_fallbacks"/>Using Builtin Atomic Functions</h3></div></div></div><p>The functions for atomic operations described above are either
|
||
implemented via compiler intrinsics (if the underlying host is
|
||
capable) or by library fallbacks.</p><p>Compiler intrinsics (builtins) are always preferred. However, as
|
||
the compiler builtins for atomics are not universally implemented,
|
||
using them directly is problematic, and can result in undefined
|
||
function calls. (An example of an undefined symbol from the use
|
||
of <code class="code">__sync_fetch_and_add</code> on an unsupported host is a
|
||
missing reference to <code class="code">__sync_fetch_and_add_4</code>.)
|
||
</p><p>In addition, on some hosts the compiler intrinsics are enabled
|
||
conditionally, via the <code class="code">-march</code> command line flag. This makes
|
||
usage vary depending on the target hardware and the flags used during
|
||
compile.
|
||
</p><p>
|
||
<em><span class="remark">
|
||
Incomplete/inconsistent. This is only C++11.
|
||
</span></em>
|
||
</p><p>
|
||
If builtins are possible for bool-sized integral types,
|
||
<code class="code">ATOMIC_BOOL_LOCK_FREE</code> will be defined.
|
||
If builtins are possible for int-sized integral types,
|
||
<code class="code">ATOMIC_INT_LOCK_FREE</code> will be defined.
|
||
</p><p>For the following hosts, intrinsics are enabled by default.
|
||
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>alpha</p></li><li class="listitem"><p>ia64</p></li><li class="listitem"><p>powerpc</p></li><li class="listitem"><p>s390</p></li></ul></div><p>For others, some form of <code class="code">-march</code> may work. On
|
||
non-ancient x86 hardware, <code class="code">-march=native</code> usually does the
|
||
trick.</p><p> For hosts without compiler intrinsics, but with capable
|
||
hardware, hand-crafted assembly is selected. This is the case for the following hosts:
|
||
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>cris</p></li><li class="listitem"><p>hppa</p></li><li class="listitem"><p>i386</p></li><li class="listitem"><p>i486</p></li><li class="listitem"><p>m48k</p></li><li class="listitem"><p>mips</p></li><li class="listitem"><p>sparc</p></li></ul></div><p>And for the rest, a simulated atomic lock via pthreads.
|
||
</p><p> Detailed information about compiler intrinsics for atomic operations can be found in the GCC <a class="link" href="http://gcc.gnu.org/onlinedocs/gcc/Atomic-Builtins.html"> documentation</a>.
|
||
</p><p> More details on the library fallbacks from the porting <a class="link" href="internals.html#internals.thread_safety" title="Thread Safety">section</a>.
|
||
</p></div><div class="section" title="Thread Abstraction"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.concurrency.impl.thread"/>Thread Abstraction</h3></div></div></div><p>A thin layer above IEEE 1003.1 (i.e. pthreads) is used to abstract
|
||
the thread interface for GCC. This layer is called "gthread," and is
|
||
comprised of one header file that wraps the host's default thread layer with
|
||
a POSIX-like interface.
|
||
</p><p> The file <gthr-default.h> points to the deduced wrapper for
|
||
the current host. In libstdc++ implementation files,
|
||
<bits/gthr.h> is used to select the proper gthreads file.
|
||
</p><p>Within libstdc++ sources, all calls to underlying thread functionality
|
||
use this layer. More detail as to the specific interface can be found in the source <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00883_source.html">documentation</a>.
|
||
</p><p>By design, the gthread layer is interoperable with the types,
|
||
functions, and usage found in the usual <pthread.h> file,
|
||
including <code class="code">pthread_t</code>, <code class="code">pthread_once_t</code>, <code class="code">pthread_create</code>,
|
||
etc.
|
||
</p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="ext_concurrency.html">Prev</a> </td><td align="center"><a accesskey="u" href="ext_concurrency.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch30s03.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 30. Concurrency </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Use</td></tr></table></div></body></html>
|