PTHREAD_AFFINITY_NP(3)                        FreeBSD Library Functions Manual

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>.

FreeBSD 15.1-STABLE-HBSD       January 29, 2023         PTHREAD_AFFINITY_NP(3)