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| <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> | |
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