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.Dd January 15, 2017
.Dt PTHREAD_ATTR_SETAFFINITY_NP 2
.Os
.Sh NAME
.Nm pthread_attr_setaffinity_np ,
.Nm pthread_attr_getaffinity_np
.Nd set and get the thread's CPU affinity mask attribute
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.In pthread_np.h
.Ft int
.Fn pthread_attr_setaffinity_np "pthread_attr_t *attr" "size_t cpusetsize" "const cpu_set_t *mask"
.Ft int
.Fn pthread_attr_getaffinity_np "const pthread_attr_t *attr" "size_t cpusetsize" "cpu_set_t *mask"
.Sh DESCRIPTION
The
.Fn pthread_attr_setaffinity_np
sets the CPU affinity mask of the
.Fa attr
to the value specified by the
.Fa mask .
The
.Fa cpusetsize
is the length (in bytes) of the data pointed to by
.Fa mask .
Normally this argument would be specified as sizeof(cpu_set_t).
The threads created by
.Xr pthread_create 3
with the
.Fa attr
will use the CPU affinity mask of the
.Fa attr .
.Pp
.Fn pthread_attr_getaffinity_np
writes the CPU affinity mask of the
.Fa attr
to the cpu_set_t structure pointed to by
.Fa mask .
.Pp
The cpu_set_t data structure represents a set of CPUs.
See
.Xr sched_setaffinity 2
for details.
.Sh RETURN VALUES
If successful,
these functions will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_attr_setaffinity_np
and
.Fn pthread_attr_getaffinity_np
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa mask
parameter is outside the process's allocated address space.
.It Bq Er EINVAL
The
.Fa attr
parameter is invalid.
.It Bq Er EPERM
The
.Fa mask
does not contain a valid CPU.
.El
.Sh SEE ALSO
.Xr pthread_create 3 ,
.Xr pthread_getaffinity_np 3 ,
.Xr pthread_setaffinity_np 3
.Sh HISTORY
The
.Fn pthread_attr_setaffinity_np
and
.Fn pthread_attr_getaffinity_np
functions first appeared in
.Dx 4.7 .