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authorrpj <rpj>2005-05-05 14:18:27 +0000
committerrpj <rpj>2005-05-05 14:18:27 +0000
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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+<HEAD>
+ <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8">
+ <TITLE>&quot;PTHREAD_GETCONCURRENCY&quot;(P) manual page</TITLE>
+ <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)">
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+<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
+<P><A HREF="#toc">Table of Contents</A></P>
+<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
+<P>pthread_getconcurrency, pthread_setconcurrency - get and set the
+level of concurrency
+</P>
+<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
+<P><B>#include &lt;pthread.h&gt; </B>
+</P>
+<P><B>int pthread_getconcurrency(void);</B> <BR><B>int
+pthread_setconcurrency(int</B> <I>new_level</I><B>); </B>
+</P>
+<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
+<P>Unbound threads in a process may or may not be required to be
+simultaneously active. By default, the threads implementation ensures
+that a sufficient number of threads are active so that the process
+can continue to make progress. While this conserves system resources,
+it may not produce the most effective level of concurrency.
+</P>
+<P>The <B>pthread_setconcurrency</B> function allows an application
+to inform the threads implementation of its desired concurrency
+level, <I>new_level</I>. The actual level of concurrency provided by
+the implementation as a result of this function call is unspecified.
+</P>
+<P>If <I>new_level</I> is zero, it causes the implementation to
+maintain the concurrency level at its discretion as if
+<B>pthread_setconcurrency</B> had never been called.
+</P>
+<P>The <B>pthread_getconcurrency</B> function shall return the value
+set by a previous call to the <B>pthread_setconcurrency</B> function.
+If the <B>pthread_setconcurrency</B> function was not previously
+called, this function shall return zero to indicate that the
+implementation is maintaining the concurrency level.
+</P>
+<P>A call to <B>pthread_setconcurrency</B> shall inform the
+implementation of its desired concurrency level. The implementation
+shall use this as a hint, not a requirement.
+</P>
+<P>If an implementation does not support multiplexing of user threads
+on top of several kernel-scheduled entities, the
+<B>pthread_setconcurrency</B> and <B>pthread_getconcurrency</B>
+functions are provided for source code compatibility but they shall
+have no effect when called. To maintain the function semantics, the
+<I>new_level</I> parameter is saved when <B>pthread_setconcurrency</B>
+is called so that a subsequent call to <B>pthread_getconcurrency</B>
+shall return the same value.
+</P>
+<P><B>Pthreads-w32</B> provides these routines for source code
+compatibility only, as described in the previous paragraph.</P>
+<H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
+<P>If successful, the <B>pthread_setconcurrency</B> function shall
+return zero; otherwise, an error number shall be returned to indicate
+the error.
+</P>
+<P>The <B>pthread_getconcurrency</B> function shall always return the
+concurrency level set by a previous call to <B>pthread_setconcurrency</B>
+. If the <B>pthread_setconcurrency</B> function has never been
+called, <B>pthread_getconcurrency</B> shall return zero.
+</P>
+<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
+<P>The <B>pthread_setconcurrency</B> function shall fail if:
+</P>
+<DL>
+ <DT><B>EINVAL</B>
+ </DT><DD>
+ The value specified by <I>new_level</I> is negative.
+ </DD><DT>
+ <B>EAGAIN</B>
+ </DT><DD STYLE="margin-bottom: 0.5cm">
+ The value specific by <I>new_level</I> would cause a system resource
+ to be exceeded.
+ </DD></DL>
+<P>
+These functions shall not return an error code of [EINTR].
+</P>
+<P><I>The following sections are informative.</I>
+</P>
+<H2><A HREF="#toc5" NAME="sect5">Examples</A></H2>
+<P>None.
+</P>
+<H2><A HREF="#toc6" NAME="sect6">Application Usage</A></H2>
+<P>Use of these functions changes the state of the underlying
+concurrency upon which the application depends. Library developers
+are advised to not use the <B>pthread_getconcurrency</B> and
+<B>pthread_setconcurrency</B> functions since their use may conflict
+with an applications use of these functions.
+</P>
+<H2><A HREF="#toc7" NAME="sect7">Rationale</A></H2>
+<P>None.
+</P>
+<H2><A HREF="#toc8" NAME="sect8">Future Directions</A></H2>
+<P>None.
+</P>
+<H2><A HREF="#toc9" NAME="sect9">See Also</A></H2>
+<P>The Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001,
+<I>&lt;pthread.h&gt;</I>
+</P>
+<H2><A HREF="#toc10" NAME="sect10">Copyright</A></H2>
+<P>Portions of this text are reprinted and reproduced in electronic
+form from IEEE Std 1003.1, 2003 Edition, Standard for Information
+Technology -- Portable Operating System Interface (POSIX), The Open
+Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the
+Institute of Electrical and Electronics Engineers, Inc and The Open
+Group. In the event of any discrepancy between this version and the
+original IEEE and The Open Group Standard, the original IEEE and The
+Open Group Standard is the referee document. The original Standard
+can be obtained online at <A HREF="http://www.opengroup.org/unix/online.html">http://www.opengroup.org/unix/online.html</A>
+.
+</P>
+<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
+<HR>
+<P><A NAME="toc"></A><B>Table of Contents</B></P>
+<UL>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return
+ Value</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Examples</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">Application
+ Usage</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">Rationale</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect8" NAME="toc8">Future
+ Directions</A>
+ </P>
+ <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect9" NAME="toc9">See
+ Also</A>
+ </P>
+ <LI><P><A HREF="#sect10" NAME="toc10">Copyright</A>
+ </P>
+</UL>
+</BODY>
+</HTML>