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<H4 CLASS="western"><FONT FACE="Times New Roman, serif"><FONT SIZE=3><SPAN STYLE="font-style: normal">POSIX
Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></SPAN></FONT></FONT></H4>
<P><A HREF="index.html">Reference Index</A></P>
<P><A HREF="#toc">Table of Contents</A></P>
<H2 CLASS="western"><A HREF="#toc0" NAME="sect0">Name</A></H2>
<P>sched_setaffinity - set process CPU affinity</P>
<P>sched_getaffinity - get process CPU affinity</P>
<H2 CLASS="western"><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
<P><B>#include <sched.h> </B>
</P>
<P><B>int sched_setaffinity(pid_t </B><I><SPAN STYLE="font-weight: normal">pid</SPAN></I><B>,
int </B><I><SPAN STYLE="font-weight: normal">cpusetsize</SPAN></I><B>,
const cpu_set_t *</B><I><SPAN STYLE="font-weight: normal">mask</SPAN></I><B>);</B></P>
<P><B>int sched_getaffinity(pid_t </B><I><SPAN STYLE="font-weight: normal">pid</SPAN></I><B>,
int </B><I><SPAN STYLE="font-weight: normal">cpusetsize</SPAN></I><B>,
cpu_set_t *</B><I><SPAN STYLE="font-weight: normal">mask</SPAN></I><B>);</B></P>
<H2 CLASS="western"><A HREF="#toc2" NAME="sect2">Description</A></H2>
<P><B>sched_setaffinity</B> sets the CPU affinity mask of the process
whose ID is <I>pid</I> to the value specified by mask. If <I>pid</I>
is zero, then the calling process is used. The argument <I>cpusetsize</I>
is the length (in bytes) of the data pointed to by <I>mask</I>.
Normally this argument would be specified as <I>sizeof(cpu_set_t)</I>.</P>
<P>If the process specified by <I>pid</I> is not currently running on
one of the CPUs specified in <I>mask</I>, then that process is
migrated to one of the CPUs specified in <I>mask</I>.</P>
<P>After a call to <B>sched_setaffinity</B>, the set of CPUs on which
the process will actually run is the intersection of the set
specified in the <I>mask</I> argument and the set of CPUs actually
present on the system.</P>
<P><B>sched_getaffinity</B> writes the affinity mask of the process
whose ID is <I>pid</I> into the cpu_set_t structure pointed to by
<I>mask</I>. The <I>cpusetsize</I> argument specifies the size (in
bytes) of <I>mask</I>. If <I>pid</I> is zero, then the mask of the
calling process is returned.</P>
<P><B>Pthreads-w32</B> currently ignores the <I>cpusetsize</I>
parameter for either function because cpu_set_t is a direct typeset
to the Windows affinity vector type DWORD_PTR.</P>
<P>Windows may require that the requesting process have permission to
set its own CPU affinity or that of another process.</P>
<H2 CLASS="western"><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
<P>On success, <B>sched_setaffinity</B> and <B>sched_getaffinity</B>
return 0. On error, -1 is returned, and <I>errno</I> is set
appropriately.</P>
<H2 CLASS="western"><A HREF="#toc4" NAME="sect4">Errors</A></H2>
<DL>
<DT><B>EFAULT</B></DT><DL>
<DL>
<DT STYLE="margin-left: 0.02cm">
A supplied memory address was invalid.</DT></DL>
</DL>
<DT>
<B>EINVAL</B></DT><DL>
<DL>
<DT STYLE="margin-left: 0.04cm">
The affinity bit mask mask contains no processors that are
currently physically on the system.</DT></DL>
</DL>
<DT>
<B>EAGAIN</B></DT><DL>
<DL>
<DT STYLE="margin-left: 0.02cm">
The function did not succeed in changing or obtaining the CPU
affinity for some undetermined reason. Try again.</DT></DL>
</DL>
<DT>
<B>EPERM</B></DT><DL>
<DL>
<DT STYLE="margin-left: 0.02cm">
The calling process does not have appropriate privileges.</DT></DL>
</DL>
<DT>
<B>ESRCH</B>
</DT><DL>
<DL>
<DT STYLE="margin-left: 0.02cm">
The process whose ID is pid could not be found.</DT></DL>
</DL>
</DL>
<H2 CLASS="western">
<A HREF="#toc5" NAME="sect5">Application Usage</A></H2>
<P>A process's CPU affinity mask determines the set of CPUs on which
it is eligible to run. On a multiprocessor system, setting the CPU
affinity mask can be used to obtain performance benefits. For
example, by dedicating one CPU to a particular process (i.e., setting
the affinity mask of that process to specify a single CPU, and
setting the affinity mask of all other processes to exclude that
CPU), it is possible to ensure maximum execution speed for that
process. Restricting a process to run on a single CPU also avoids the
performance cost caused by the cache invalidation that occurs when a
process ceases to execute on one CPU and then recommences execution
on a different CPU.</P>
<P>A CPU affinity mask is represented by the cpu_set_t structure, a
"CPU set", pointed to by <I>mask</I>. A set of macros for
manipulating CPU sets is described in <B>cpu_set</B>(3).</P>
<H2 CLASS="western"><A HREF="#toc6" NAME="sect6">See Also</A></H2>
<P><A HREF="cpu_set.html"><B>cpu_set</B>(3)</A>,
<A HREF="pthread_setaffinity_np.html"><B>pthread_setaffininty_np</B>(3)</A>,
<A HREF="pthread_setaffinity_np.html"><B>pthread_getaffinity_np</B>(3)</A></P>
<H2 CLASS="western"><A HREF="#toc7" NAME="sect7">Copyright</A></H2>
<P>Most of this is taken from the Linux manual page.</P>
<P>Modified by Ross Johnson for use with <B>Pthreads-w32</B>.</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">Application
Usage</A></P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See
Also</A></P>
<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">Copyright</A></P>
</UL>
<H4 CLASS="western"><BR><BR>
</H4>
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