NAME

pthread_getaffinity_np, pthread_setaffinity_np — manage CPU affinity

LIBRARY

POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

#include <pthread_np.h>

int
pthread_getaffinity_np(pthread_t td, size_t cpusetsize, cpuset_t *cpusetp);

int
pthread_setaffinity_np(pthread_t td, size_t cpusetsize, const cpuset_t *cpusetp);

DESCRIPTION

pthread_getaffinity_np() and pthread_setaffinity_np() allow the manipulation of sets of CPUs available to the specified thread.

Masks of type cpuset_t are composed using the CPU_SET macros. If the user-supplied mask is not large enough to fit all of the matching CPUs, pthread_getaffinity_np() fails with ERANGE. Calls to pthread_setaffinity_np() tolerate masks of any size with no restrictions. The kernel uses the meaningful part of the mask, where the upper bound is the maximum CPU id present in the system. If bits for non-existing CPUs are set, calls to pthread_setaffinity_np() fail with EINVAL.

The supplied mask should have a size of cpusetsize bytes. This size is usually provided by calling sizeof(cpuset_t) which is ultimately determined by the value of CPU_SETSIZE as defined in <sys/cpuset.h>.

pthread_getaffinity_np() retrieves the mask from the thread specified by td, and stores it in the space provided by cpusetp.

pthread_setaffinity_np() attempts to set the mask for the thread specified by td to the value in cpusetp.

RETURN VALUES

If successful, the pthread_getaffinity_np() and pthread_setaffinity_np() functions will return zero. Otherwise an error number will be returned to indicate the error.

ERRORS

The pthread_getaffinity_np() and pthread_setaffinity_np() functions may fail if:

[EINVAL]

The cpusetp argument specified when calling pthread_setaffinity_np() was not a valid value.

[EDEADLK]

The pthread_setaffinity_np() call would leave a thread without a valid CPU to run on because the set does not overlap with the thread's anonymous mask.

[EFAULT]

The cpusetp pointer passed was invalid.

[ESRCH]

The thread specified by the td argument could not be found.

[ERANGE]

The cpusetsize was smaller than needed to fit all of the matching CPUs.

[EPERM]

The calling thread did not have the credentials required to complete the operation.

SEE ALSO

cpuset(1), cpuset(2), cpuset_getid(2), cpuset_setid(2), pthread(3), pthread_attr_getaffinity_np(3), pthread_attr_setaffinity_np(3), pthread_np(3)

STANDARDS

The pthread_getaffinity_np and pthread_setaffinity_np functions are non-standard FreeBSD extensions and may be not available on other operating systems.

HISTORY

The pthread_getaffinity_np and pthread_setaffinity_np function first appeared in FreeBSD 7.2.

AUTHORS

The pthread_getaffinity_np and pthread_setaffinity_np functions were written by David Xu <davidxu@FreeBSD.org>, and this manpage was written by Xin LI <delphij@FreeBSD.org>.