NAME         top

       pthread_setaffinity_np, pthread_getaffinity_np - set/get CPU affinity
       of a thread

SYNOPSIS         top

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <pthread.h>

       int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize,
                                  const cpu_set_t *cpuset);
       int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize,
                                  cpu_set_t *cpuset);

       Compile and link with -pthread.

DESCRIPTION         top

       The pthread_setaffinity_np() function sets the CPU affinity mask of
       the thread thread to the CPU set pointed to by cpuset.  If the call
       is successful, and the thread is not currently running on one of the
       CPUs in cpuset, then it is migrated to one of those CPUs.

       The pthread_getaffinity_np() function returns the CPU affinity mask
       of the thread thread in the buffer pointed to by cpuset.

       For more details on CPU affinity masks, see sched_setaffinity(2).
       For a description of a set of macros that can be used to manipulate
       and inspect CPU sets, see CPU_SET(3).

       The argument cpusetsize is the length (in bytes) of the buffer
       pointed to by cpuset.  Typically, this argument would be specified as
       sizeof(cpu_set_t).  (It may be some other value, if using the macros
       described in CPU_SET(3) for dynamically allocating a CPU set.)

RETURN VALUE         top

       On success, these functions return 0; on error, they return a nonzero
       error number.

ERRORS         top

       EFAULT A supplied memory address was invalid.

       EINVAL (pthread_setaffinity_np()) The affinity bit mask mask contains
              no processors that are currently physically on the system and
              permitted to the thread according to any restrictions that may
              be imposed by the "cpuset" mechanism described in cpuset(7).

       EINVAL (pthread_setaffinity_np()) cpuset specified a CPU that was
              outside the set supported by the kernel.  (The kernel
              configuration option CONFIG_NR_CPUS defines the range of the
              set supported by the kernel data type used to represent CPU

       EINVAL (pthread_getaffinity_np()) cpusetsize is smaller than the size
              of the affinity mask used by the kernel.

       ESRCH  No thread with the ID thread could be found.

VERSIONS         top

       These functions are provided by glibc since version 2.3.4.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                 Attribute     Value   │
       │pthread_setaffinity_np(), │ Thread safety │ MT-Safe │
       │pthread_getaffinity_np()  │               │         │

CONFORMING TO         top

       These functions are nonstandard GNU extensions; hence the suffix
       "_np" (nonportable) in the names.

NOTES         top

       After a call to pthread_setaffinity_np(), the set of CPUs on which
       the thread will actually run is the intersection of the set specified
       in the cpuset argument and the set of CPUs actually present on the
       system.  The system may further restrict the set of CPUs on which the
       thread runs if the "cpuset" mechanism described in cpuset(7) is being
       used.  These restrictions on the actual set of CPUs on which the
       thread will run are silently imposed by the kernel.

       These functions are implemented on top of the sched_setaffinity(2)
       and sched_getaffinity(2) system calls.

       In glibc 2.3.3 only, versions of these functions were provided that
       did not have a cpusetsize argument.  Instead the CPU set size given
       to the underlying system calls was always sizeof(cpu_set_t).

       A new thread created by pthread_create(3) inherits a copy of its
       creator's CPU affinity mask.

EXAMPLE         top

       In the following program, the main thread uses
       pthread_setaffinity_np() to set its CPU affinity mask to include CPUs
       0 to 7 (which may not all be available on the system), and then calls
       pthread_getaffinity_np() to check the resulting CPU affinity mask of
       the thread.

       #define _GNU_SOURCE
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
               do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       main(int argc, char *argv[])
           int s, j;
           cpu_set_t cpuset;
           pthread_t thread;

           thread = pthread_self();

           /* Set affinity mask to include CPUs 0 to 7 */

           for (j = 0; j < 8; j++)
               CPU_SET(j, &cpuset);

           s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
           if (s != 0)
               handle_error_en(s, "pthread_setaffinity_np");

           /* Check the actual affinity mask assigned to the thread */

           s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
           if (s != 0)
               handle_error_en(s, "pthread_getaffinity_np");

           printf("Set returned by pthread_getaffinity_np() contained:\n");
           for (j = 0; j < CPU_SETSIZE; j++)
               if (CPU_ISSET(j, &cpuset))
                   printf("    CPU %d\n", j);


SEE ALSO         top

       sched_setaffinity(2), CPU_SET(3).  pthread_attr_setaffinity_np(3),
       pthread_self(3), sched_getcpu(3), cpuset(7), pthreads(7), sched(7)

COLOPHON         top

       This page is part of release 4.06 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2016-03-15        PTHREAD_SETAFFINITY_NP(3)