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-<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Concurrency</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++ , runtime , library "/><link rel="home" href="../index.html" title="The GNU C++ Library"/><link rel="up" href="using.html" title="Chapter 3. Using"/><link rel="prev" href="using_dynamic_or_shared.html" title="Linking"/><link rel="next" href="using_exceptions.html" title="Exceptions"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Concurrency</th></tr><tr><td align="left"><a accesskey="p" href="using_dynamic_or_shared.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Using</th><td align="right"> <a accesskey="n" href="using_exceptions.html">Next</a></td></tr></table><hr/></div><div class="section" title="Concurrency"><div class="titlepage"><div><div><h2 class="title"><a id="manual.intro.using.concurrency"/>Concurrency</h2></div></div></div><p>This section discusses issues surrounding the proper compilation
+<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Concurrency</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++
+ ,
+ runtime
+ ,
+ library
+ "><link rel="home" href="../index.html" title="The GNU C++ Library"><link rel="up" href="using.html" title="Chapter 3. Using"><link rel="prev" href="using_dynamic_or_shared.html" title="Linking"><link rel="next" href="using_exceptions.html" title="Exceptions"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Concurrency</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="using_dynamic_or_shared.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Using</th><td width="20%" align="right"> <a accesskey="n" href="using_exceptions.html">Next</a></td></tr></table><hr></div><div class="section" title="Concurrency"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manual.intro.using.concurrency"></a>Concurrency</h2></div></div></div><p>This section discusses issues surrounding the proper compilation
of multithreaded applications which use the Standard C++
library. This information is GCC-specific since the C++
standard does not address matters of multithreaded applications.
- </p><div class="section" title="Prerequisites"><div class="titlepage"><div><div><h3 class="title"><a
id="manual.intro.using.concurrency.prereq"/>Prerequisites</h3></div></div></div><p>All normal disclaimers aside, multithreaded C++ application are
+ </p><div class="section" title="Prerequisites"><div class="titlepage"><div><div><h3 class="title"><a
name="manual.intro.using.concurrency.prereq"></a>Prerequisites</h3></div></div></div><p>All normal disclaimers aside, multithreaded C++ application are
only supported when libstdc++ and all user code was built with
compilers which report (via <code class="code"> gcc/g++ -v </code>) the same thread
model and that model is not <span class="emphasis"><em>single</em></span>. As long as your
-pthread is honored. Some other ports use other switches.
AFAIK, none of this is properly documented anywhere other than
in ``gcc -dumpspecs'' (look at lib and cpp entries).
- </p></div><div class="section" title="Thread Safety"><div class="titlepage"><div><div><h3 class="title"><a
id="manual.intro.using.concurrency.thread_safety"/>Thread Safety</h3></div></div></div><p>
+ </p></div><div class="section" title="Thread Safety"><div class="titlepage"><div><div><h3 class="title"><a
name="manual.intro.using.concurrency.thread_safety"></a>Thread Safety</h3></div></div></div><p>
In the terms of the 2011 C++ standard a thread-safe program is one which
does not perform any conflicting non-atomic operations on memory locations
and so does not contain any data races.
races are caused by the library itself or by programs which use the
library correctly (as described below).
The C++11 memory model and library requirements are a more formal version
-of the <a class="link" href="http://www.sgi.com/tech/stl/thread_safety.html">SGI STL</a> definition of thread safety, which the library used
+of the <a class="link" href="http://www.sgi.com/tech/stl/thread_safety.html" target="_top">SGI STL</a> definition of thread safety, which the library used
prior to the 2011 standard.
</p><p>The library strives to be thread-safe when all of the following
conditions are met:
- </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>The system's libc is itself thread-safe,
+ </p><div class="itemizedlist"><ul class="itemizedlist"
type="disc"><li class="listitem"><p>The system's libc is itself thread-safe,
</p></li><li class="listitem"><p>
The compiler in use reports a thread model other than
'single'. This can be tested via output from <code class="code">gcc
Requisite command-line flags are used for atomic operations
and threading. Examples of this include <code class="code">-pthread</code>
and <code class="code">-march=native</code>, although specifics vary
- depending on the host environment. See <a class="link" href="http://gcc.gnu.org/onlinedocs/gcc/Option-Summary.html">Machine
+ depending on the host environment. See <a class="link" href="http://gcc.gnu.org/onlinedocs/gcc/Option-Summary.html" target="_top">Machine
Dependent Options</a>.
</p></li><li class="listitem"><p>
An implementation of atomicity.h functions
t2.join();
}
</pre><p>For further details of the C++11 memory model see Hans-J. Boehm's
- <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html">Threads
- and memory model for C++</a> pages, particularly the <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/threadsintro.html">introduction</a>
- and <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html">FAQ</a>.
- </p></div><div class="section" title="Atomics"><div class="titlepage"><div><div><h3 class="title"><a
id="manual.intro.using.concurrency.atomics"/>Atomics</h3></div></div></div><p>
- </p></div><div class="section" title="IO"><div class="titlepage"><div><div><h3 class="title"><a
id="manual.intro.using.concurrency.io"/>IO</h3></div></div></div><p>This gets a bit tricky. Please read carefully, and bear with me.
- </p><div class="section" title="Structure"><div class="titlepage"><div><div><h4 class="title"><a
id="concurrency.io.structure"/>Structure</h4></div></div></div><p>A wrapper
+ <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html" target="_top">Threads
+ and memory model for C++</a> pages, particularly the <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/threadsintro.html" target="_top">introduction</a>
+ and <a class="link" href="http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/user-faq.html" target="_top">FAQ</a>.
+ </p></div><div class="section" title="Atomics"><div class="titlepage"><div><div><h3 class="title"><a
name="manual.intro.using.concurrency.atomics"></a>Atomics</h3></div></div></div><p>
+ </p></div><div class="section" title="IO"><div class="titlepage"><div><div><h3 class="title"><a
name="manual.intro.using.concurrency.io"></a>IO</h3></div></div></div><p>This gets a bit tricky. Please read carefully, and bear with me.
+ </p><div class="section" title="Structure"><div class="titlepage"><div><div><h4 class="title"><a
name="concurrency.io.structure"></a>Structure</h4></div></div></div><p>A wrapper
type called <code class="code">__basic_file</code> provides our abstraction layer
for the <code class="code">std::filebuf</code> classes. Nearly all decisions dealing
with actual input and output must be made in <code class="code">__basic_file</code>.
but is not used in the current code. Providing locking at any higher
level is akin to providing locking within containers, and is not done
for the same reasons (see the links above).
- </p></div><div class="section" title="Defaults"><div class="titlepage"><div><div><h4 class="title"><a
id="concurrency.io.defaults"/>Defaults</h4></div></div></div><p>The __basic_file type is simply a collection of small wrappers around
+ </p></div><div class="section" title="Defaults"><div class="titlepage"><div><div><h4 class="title"><a
name="concurrency.io.defaults"></a>Defaults</h4></div></div></div><p>The __basic_file type is simply a collection of small wrappers around
the C stdio layer (again, see the link under Structure). We do no
locking ourselves, but simply pass through to calls to <code class="code">fopen</code>,
<code class="code">fwrite</code>, and so forth.
contained in the stream formatting classes (e.g., setting up callbacks
inside an <code class="code">std::ofstream</code>), you need to guard such accesses
like any other critical shared resource.
- </p></div><div class="section" title="Future"><div class="titlepage"><div><div><h4 class="title"><a
id="concurrency.io.future"/>Future</h4></div></div></div><p> A
+ </p></div><div class="section" title="Future"><div class="titlepage"><div><div><h4 class="title"><a
name="concurrency.io.future"></a>Future</h4></div></div></div><p> A
second choice may be available for I/O implementations: libio. This is
disabled by default, and in fact will not currently work due to other
issues. It will be revisited, however.
version will see calls from libstdc++ directly into the glibc already
installed. For other platforms, a copy of the libio subsection will
be built and included in libstdc++.
- </p></div><div class="section" title="Alternatives"><div class="titlepage"><div><div><h4 class="title"><a
id="concurrency.io.alt"/>Alternatives</h4></div></div></div><p>Don't forget that other cstdio implementations are possible. You could
+ </p></div><div class="section" title="Alternatives"><div class="titlepage"><div><div><h4 class="title"><a
name="concurrency.io.alt"></a>Alternatives</h4></div></div></div><p>Don't forget that other cstdio implementations are possible. You could
easily write one to perform your own forms of locking, to solve your
"interesting" problems.
- </p></div></div><div class="section" title="Containers"><div class="titlepage"><div><div><h3 class="title"><a
id="manual.intro.using.concurrency.containers"/>Containers</h3></div></div></div><p>This section discusses issues surrounding the design of
+ </p></div></div><div class="section" title="Containers"><div class="titlepage"><div><div><h3 class="title"><a
name="manual.intro.using.concurrency.containers"></a>Containers</h3></div></div></div><p>This section discusses issues surrounding the design of
multithreaded applications which use Standard C++ containers.
All information in this section is current as of the gcc 3.0
release and all later point releases. Although earlier gcc
threaded and non-threaded code), see Chapter 17.
</p><p>Two excellent pages to read when working with the Standard C++
containers and threads are
- <a class="link" href="http://www.sgi.com/tech/stl/thread_safety.html">SGI's
+ <a class="link" href="http://www.sgi.com/tech/stl/thread_safety.html" target="_top">SGI's
http://www.sgi.com/tech/stl/thread_safety.html</a> and
- <a class="link" href="http://www.sgi.com/tech/stl/Allocators.html">SGI's
+ <a class="link" href="http://www.sgi.com/tech/stl/Allocators.html" target="_top">SGI's
http://www.sgi.com/tech/stl/Allocators.html</a>.
</p><p><span class="emphasis"><em>However, please ignore all discussions about the user-level
configuration of the lock implementation inside the STL
useful are details
on <a class="link" href="memory.html#std.util.memory.allocator" title="Allocators">allocator</a>
options and capabilities.
- </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="using_dynamic_or_shared.html">Prev</a> </td><td align="center"><a accesskey="u" href="using.html">Up</a></td><td align="right"> <a accesskey="n" href="using_exceptions.html">Next</a></td></tr><tr><td align="left" valign="top">Linking </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Exceptions</td></tr></table></div></body></html>
+ </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="using_dynamic_or_shared.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="using.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="using_exceptions.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Linking </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Exceptions</td></tr></table></div></body></html>
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