<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8"> <TITLE>"PTHREAD_GETCONCURRENCY"(P) manual page</TITLE> <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)"> <META NAME="CREATED" CONTENT="20050505;19162600"> <META NAME="CHANGED" CONTENT="20050505;19223800"> <!-- manual page source format generated by PolyglotMan v3.2, --> <!-- available at http://polyglotman.sourceforge.net/ --> </HEAD> <BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR"> <H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4> <P><A HREF="index.html">Reference Index</A></P> <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 <pthread.h> </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 Std 1003.1-2001, <I><pthread.h></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>