NAME
pthread_setaffinity_np,
pthread_getaffinity_np —
affinity of threads
LIBRARY
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.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:
- [
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)