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.Dd January 29, 2023
.Dt PTHREAD_AFFINITY_NP 3
.Os
.Sh NAME
.Nm pthread_getaffinity_np ,
.Nm pthread_setaffinity_np
.Nd manage CPU affinity
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread_np.h
.Ft int
.Fn pthread_getaffinity_np "pthread_t td" "size_t cpusetsize" "cpuset_t *cpusetp"
.Ft int
.Fn pthread_setaffinity_np "pthread_t td" "size_t cpusetsize" "const cpuset_t *cpusetp"
.Sh DESCRIPTION
.Fn pthread_getaffinity_np
and
.Fn pthread_setaffinity_np
allow the manipulation of sets of CPUs available to the specified thread.
.Pp
Masks of type
.Ft cpuset_t
are composed using the
.Dv CPU_SET
macros.
If the user-supplied mask is not large enough to fit all of the matching CPUs,
.Fn pthread_getaffinity_np
fails with
.Er ERANGE .
Calls to
.Fn 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
.Fn pthread_setaffinity_np
fails with
.Er EINVAL .
.Pp
The supplied mask should have a size of
.Fa cpusetsize
bytes.
This size is usually provided by calling
.Li sizeof(cpuset_t)
which is ultimately determined by the value of
.Dv CPU_SETSIZE
as defined in
.In sys/cpuset.h .
.Pp
.Fn pthread_getaffinity_np
retrieves the
mask from the thread specified by
.Fa td ,
and stores it in the space provided by
.Fa cpusetp .
.Pp
.Fn pthread_setaffinity_np
attempts to set the mask for the thread specified by
.Fa td
to the value in
.Fa cpusetp .
.Sh RETURN VALUES
If successful, the
.Fn pthread_getaffinity_np
and
.Fn pthread_setaffinity_np
functions will return zero.
Otherwise an error number will be returned
to indicate the error.
.Sh ERRORS
The
.Fn pthread_getaffinity_np
and
.Fn pthread_setaffinity_np
functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa cpusetp
argument specified when calling
.Fn pthread_setaffinity_np
was not a valid value.
.It Bq Er EDEADLK
The
.Fn 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.
.It Bq Er EFAULT
The
.Fa cpusetp
pointer passed was invalid.
.It Bq Er ESRCH
The thread specified by the
.Fa td
argument could not be found.
.It Bq Er ERANGE
The
.Fa cpusetsize
was smaller than needed to fit all of the matching CPUs.
.It Bq Er EPERM
The calling thread did not have the credentials required to complete the
operation.
.El
.Sh SEE ALSO
.Xr cpuset 1 ,
.Xr cpuset 2 ,
.Xr cpuset_getid 2 ,
.Xr cpuset_setid 2 ,
.Xr pthread 3 ,
.Xr pthread_attr_getaffinity_np 3 ,
.Xr pthread_attr_setaffinity_np 3 ,
.Xr pthread_np 3
.Sh STANDARDS
The
.Nm pthread_getaffinity_np
and
.Nm pthread_setaffinity_np
functions are non-standard
.Fx
extensions and may be not available on other operating systems.
.Sh HISTORY
The
.Nm pthread_getaffinity_np
and
.Nm pthread_setaffinity_np
function first appeared in
.Fx 7.2 .
.Sh AUTHORS
.An -nosplit
The
.Nm pthread_getaffinity_np
and
.Nm pthread_setaffinity_np
functions were written by
.An David Xu Aq Mt davidxu@FreeBSD.org ,
and this manpage was written by
.An Xin LI Aq Mt delphij@FreeBSD.org .