AFFINITY(3) BSD Library Functions Manual AFFINITY(3)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. Ordi‐
nary 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:
[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 ALSOcpuset(3), pset(3), pthread_getschedparam(3), pthread_setschedparam(3),
sched(3), schedctl(8)BSD December 4, 2011 BSD
