NAME

pthread_setaffinity_np, pthread_getaffinity_np — affinity of threads

LIBRARY

POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

#include <pthread.h>
#include <sched.h>

int
pthread_setaffinity_np(pthread_t thread, size_t size, cpuset_t *set);

int
pthread_getaffinity_np(pthread_t thread, size_t size, cpuset_t *set);

DESCRIPTION

Thread affinity allows to run the thread on specified CPU or CPUs only.

The pthread_setaffinity_np() function sets the affinity mask set for thread. At least one valid CPU must be set in the mask.

The pthread_getaffinity_np() function gets the affinity mask of thread into set. Note that set must be created and initialized using the cpuset(3) functions.

IMPLEMENTATION NOTES

Setting CPU pthread_setaffinity_np requires super-user privileges. Ordinary users can be allowed to control CPU affinity of their threads via the security.models.extensions.user_set_cpu_affinity sysctl(7). See secmodel_extensions(9).

Portable applications should not use the pthread_setaffinity_np() and pthread_getaffinity_np() functions.

RETURN VALUES

The pthread_setaffinity_np() and pthread_getaffinity_np() functions return 0 on success. Otherwise, an error number is returned to indicate the error.

EXAMPLES

An example of code fragment, which sets the affinity for the current thread to the CPU whose ID is 0:

	cpuset_t *cset;
	pthread_t pth;
	cpuid_t ci;
	int error;

	cset = cpuset_create();
	if (cset == NULL) {
		err(EXIT_FAILURE, "cpuset_create");
	}
	ci = 0;
	cpuset_set(ci, cset);

	pth = pthread_self();
	error = pthread_setaffinity_np(pth, cpuset_size(cset), cset);
	if (error) {
		errc(EXIT_FAILURE, error, "pthread_setaffinity_np failed");
	}
	cpuset_destroy(cset);

COMPATIBILITY

Both functions are non-standard extensions.

ERRORS

Both functions may fail if:

[EINVAL]: The specified set was invalid.
[EPERM]: The calling process lacks the appropriate privileges to perform the operation.
[ESRCH]: No thread could be found corresponding to the one specified by thread.

NOTES

There is an alternative processor sets interface, see pset(3). However, thread affinity and processor sets are mutually exclusive, hence mixing of these interfaces is prohibited.