AFFINITY(3)

NAME
pthread_setaffinity_np, pthread_getaffinity_np - affinity of threads

LIBRARY
libpthread

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.

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.

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);

ERRORS
The pthread_setaffinity_np() and pthread_getaffinity_np() functions 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.

SEE ALSO
cpuset(3), pset(3), pthread_getschedparam(3), pthread_setschedparam(3), sched(3), schedctl(8)