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pthread_attr_setaffinity_np - Man Page

set/get CPU affinity attribute in thread attributes object


POSIX threads library (libpthread, -lpthread)


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

int pthread_attr_setaffinity_np(pthread_attr_t *attr,
                   size_t cpusetsize, const cpu_set_t *cpuset);
int pthread_attr_getaffinity_np(const pthread_attr_t *attr,
                   size_t cpusetsize, cpu_set_t *cpuset);


The pthread_attr_setaffinity_np() function sets the CPU affinity mask attribute of the thread attributes object referred to by attr to the value specified in cpuset. This attribute determines the CPU affinity mask of a thread created using the thread attributes object attr.

The pthread_attr_getaffinity_np() function returns the CPU affinity mask attribute of the thread attributes object referred to by attr in the buffer pointed to by cpuset.

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).

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).

Return Value

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



(pthread_attr_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 sets.)


(pthread_attr_getaffinity_np()) A CPU in the affinity mask of the thread attributes object referred to by attr lies outside the range specified by cpusetsize (i.e., cpuset/cpusetsize is too small).


(pthread_attr_setaffinity_np()) Could not allocate memory.


For an explanation of the terms used in this section, see attributes(7).

pthread_attr_setaffinity_np(), pthread_attr_getaffinity_np()Thread safetyMT-Safe


GNU; hence the suffix "_np" (nonportable) in the names.


glibc 2.3.4.


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).

See Also

sched_setaffinity(2), pthread_attr_init(3), pthread_setaffinity_np(3), cpuset(7), pthreads(7)

Referenced By

CPU_SET(3), pthread_attr_init(3), pthread_attr_setscope(3), pthread_getattr_default_np(3), pthread_getattr_np(3), pthread_setaffinity_np(3).

The man page pthread_attr_getaffinity_np(3) is an alias of pthread_attr_setaffinity_np(3).

2024-05-02 Linux man-pages 6.9.1