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; 
 
	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) { 
		... 
	} 
	cpuset_destroy(cset);

COMPATIBILITY

Both functions are non-standard extensions.

ERRORS

Both functions may fail if:

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.