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Dd February 21, 2025
Dt AFFINITY 3
Os
Sh NAME
Nm pthread_setaffinity_np ,
Nm pthread_getaffinity_np
Nd affinity of threads
Sh LIBRARY
Lb libpthread
Sh SYNOPSIS
In pthread.h
In sched.h
Ft int
Fn pthread_setaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
Ft int
Fn pthread_getaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
Sh DESCRIPTION
Thread affinity allows to run the thread on specified CPU or CPUs only.
Pp
The
Fn pthread_setaffinity_np
function sets the affinity mask
Fa set
for
Fa thread .
At least one valid CPU must be set in the mask.
Pp
The
Fn pthread_getaffinity_np
function gets the affinity mask of
Fa thread
into
Fa set .
Note that
Fa set
must be created and initialized using the
Xr cpuset 3
functions.
Sh IMPLEMENTATION NOTES
Setting CPU
Nm
requires super-user privileges.
Ordinary users can be allowed to control CPU affinity
of their threads via the
Pa security.models.extensions.user_set_cpu_affinity
Xr sysctl 7 .
See
Xr secmodel_extensions 9 .
Pp
Portable applications should not use the
Fn pthread_setaffinity_np
and
Fn pthread_getaffinity_np
functions.
Sh RETURN VALUES
The
Fn pthread_setaffinity_np
and
Fn pthread_getaffinity_np
functions return 0 on success.
Otherwise, an error number is returned to indicate the error.
Sh EXAMPLES
An example of code fragment, which sets the affinity for the current
thread to the CPU whose ID is 0:
Bd -literal
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);
Ed
Sh COMPATIBILITY
Both functions are non-standard extensions.
Sh ERRORS
Both functions may fail if:
Bl -tag -width Er
It Bq Er EINVAL
The specified
Fa set
was invalid.
It Bq Er EPERM
The calling process lacks the appropriate privileges to perform
the operation.
It Bq Er ESRCH
No thread could be found corresponding to the one specified by
Fa thread .
El
Sh NOTES
There is an alternative processor sets interface, see
Xr pset 3 .
However, thread affinity and processor sets are mutually exclusive,
hence mixing of these interfaces is prohibited.
Sh SEE ALSO
Xr cpuset 3 ,
Xr pset 3 ,
Xr pthread_getschedparam 3 ,
Xr pthread_setschedparam 3 ,
Xr sched 3 ,
Xr schedctl 8
