mirror of https://github.com/mkerrisk/man-pages
224 lines
6.4 KiB
Groff
224 lines
6.4 KiB
Groff
.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH PTHREAD_SETAFFINITY_NP 3 2016-12-12 "Linux" "Linux Programmer's Manual"
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.SH NAME
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pthread_setaffinity_np, pthread_getaffinity_np \- set/get
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CPU affinity of a thread
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.SH SYNOPSIS
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.nf
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.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
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.B #include <pthread.h>
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.PP
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.BI "int pthread_setaffinity_np(pthread_t " thread ", size_t " cpusetsize ,
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.BI " const cpu_set_t *" cpuset );
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.BI "int pthread_getaffinity_np(pthread_t " thread ", size_t " cpusetsize ,
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.BI " cpu_set_t *" cpuset );
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.PP
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Compile and link with \fI\-pthread\fP.
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.fi
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.SH DESCRIPTION
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The
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.BR pthread_setaffinity_np ()
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function
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sets the CPU affinity mask of the thread
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.I thread
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to the CPU set pointed to by
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.IR cpuset .
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If the call is successful,
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and the thread is not currently running on one of the CPUs in
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.IR cpuset ,
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then it is migrated to one of those CPUs.
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.PP
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The
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.BR pthread_getaffinity_np ()
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function returns the CPU affinity mask of the thread
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.I thread
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in the buffer pointed to by
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.IR cpuset .
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.PP
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For more details on CPU affinity masks, see
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.BR sched_setaffinity (2).
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For a description of a set of macros
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that can be used to manipulate and inspect CPU sets, see
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.BR CPU_SET (3).
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.PP
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The argument
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.I cpusetsize
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is the length (in bytes) of the buffer pointed to by
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.IR cpuset .
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Typically, this argument would be specified as
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.IR sizeof(cpu_set_t) .
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(It may be some other value, if using the macros described in
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.BR CPU_SET (3)
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for dynamically allocating a CPU set.)
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.SH RETURN VALUE
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On success, these functions return 0;
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on error, they return a nonzero error number.
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.SH ERRORS
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.TP
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.B EFAULT
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A supplied memory address was invalid.
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.TP
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.B EINVAL
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.RB ( pthread_setaffinity_np ())
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The affinity bit mask
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.I mask
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contains no processors that are currently physically on the system
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and permitted to the thread according to any restrictions that
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may be imposed by the "cpuset" mechanism described in
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.BR cpuset (7).
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.TP
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.BR EINVAL
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.RB ( pthread_setaffinity_np ())
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.I cpuset
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specified a CPU that was outside the set supported by the kernel.
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(The kernel configuration option
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.BR CONFIG_NR_CPUS
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defines the range of the set supported by the kernel data type
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.\" cpumask_t
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used to represent CPU sets.)
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.\" The raw sched_getaffinity() system call returns the size (in bytes)
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.\" of the cpumask_t type.
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.TP
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.B EINVAL
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.RB ( pthread_getaffinity_np ())
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.I cpusetsize
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is smaller than the size of the affinity mask used by the kernel.
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.TP
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.B ESRCH
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No thread with the ID
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.I thread
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could be found.
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.SH VERSIONS
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These functions are provided by glibc since version 2.3.4.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lbw25 lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR pthread_setaffinity_np (),
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.BR pthread_getaffinity_np ()
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T} Thread safety MT-Safe
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.TE
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.SH CONFORMING TO
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These functions are nonstandard GNU extensions;
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hence the suffix "_np" (nonportable) in the names.
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.SH NOTES
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After a call to
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.BR pthread_setaffinity_np (),
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the set of CPUs on which the thread will actually run is
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the intersection of the set specified in the
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.I cpuset
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argument and the set of CPUs actually present on the system.
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The system may further restrict the set of CPUs on which the thread
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runs if the "cpuset" mechanism described in
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.BR cpuset (7)
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is being used.
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These restrictions on the actual set of CPUs on which the thread
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will run are silently imposed by the kernel.
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.PP
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These functions are implemented on top of the
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.BR sched_setaffinity (2)
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and
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.BR sched_getaffinity (2)
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system calls.
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.PP
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In glibc 2.3.3 only,
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versions of these functions were provided that did not have a
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.I cpusetsize
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argument.
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Instead the CPU set size given to the underlying system calls was always
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.IR sizeof(cpu_set_t) .
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.PP
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A new thread created by
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.BR pthread_create (3)
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inherits a copy of its creator's CPU affinity mask.
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.SH EXAMPLE
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In the following program, the main thread uses
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.BR pthread_setaffinity_np ()
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to set its CPU affinity mask to include CPUs 0 to 7
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(which may not all be available on the system),
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and then calls
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.BR pthread_getaffinity_np ()
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to check the resulting CPU affinity mask of the thread.
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.PP
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.nf
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#define _GNU_SOURCE
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <errno.h>
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#define handle_error_en(en, msg) \\
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do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
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int
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main(int argc, char *argv[])
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{
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int s, j;
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cpu_set_t cpuset;
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pthread_t thread;
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thread = pthread_self();
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/* Set affinity mask to include CPUs 0 to 7 */
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CPU_ZERO(&cpuset);
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for (j = 0; j < 8; j++)
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CPU_SET(j, &cpuset);
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s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
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if (s != 0)
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handle_error_en(s, "pthread_setaffinity_np");
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/* Check the actual affinity mask assigned to the thread */
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s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
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if (s != 0)
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handle_error_en(s, "pthread_getaffinity_np");
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printf("Set returned by pthread_getaffinity_np() contained:\\n");
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for (j = 0; j < CPU_SETSIZE; j++)
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if (CPU_ISSET(j, &cpuset))
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printf(" CPU %d\\n", j);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH SEE ALSO
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.BR sched_setaffinity (2),
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.BR CPU_SET (3),
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.BR pthread_attr_setaffinity_np (3),
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.BR pthread_self (3),
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.BR sched_getcpu (3),
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.BR cpuset (7),
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.BR pthreads (7),
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.BR sched (7)
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