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. The kernel tolerates large sets as long as all CPUs specified in the set exist. Sets smaller than the kernel uses generate an error on calls to pthread_getaffinity_np() even if the result set would fit within the user supplied set. Calls to pthread_setaffinity_np() tolerate small sets with no restrictions.

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:

[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 either preposterously large or smaller than the kernel set size.
[EPERM]: The calling thread did not have the credentials required to complete the operation.

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>.