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.Dd January 14, 2017
.Dt LWP_SETAFFINITY 2
.Os
.Sh NAME
.Nm lwp_setaffinity ,
.Nm lwp_getaffinity
.Nd set and get a LWP's CPU affinity mask
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/lwp.h
.Ft int
.Fn lwp_setaffinity "pid_t pid" "lwpid_t tid" "const cpumask_t *mask"
.Ft int
.Fn lwp_getaffinity "pid_t pid" "lwpid_t tid" "cpumask_t *mask"
.Sh DESCRIPTION
The
.Fn lwp_setaffinity
system call sets the CPU affinity mask of the LWP,
which is identified by the
.Fa pid
and the
.Fa tid ,
to the value specified by the
.Fa mask .
If the
.Fa pid
is zero,
then the pid of the calling process is used.
If the
.Fa tid
is less than zero,
then all LWPs of the process identified by the
.Fa pid
are affected.
If the LWP specified by the
.Fa pid
and the
.Fa tid
is the current LWP it will be migrated immediately,
if necessary, otherwise it will be migrated by the scheduler later.
.Pp
A process created by
.Xr fork 2 ,
.Xr vfork 2 ,
and
.Xr rfork 2
inherits the calling LWP's CPU affinity mask.
Same applies to the LWPs created by
.Xr lwp_create 2 ,
and the threads created by
.Xr pthread_create 3 .
.Pp
.Fn lwp_getaffinity
writes the affinity mask of the LWP,
which is identified by the
.Fa pid
and the
.Fa tid ,
to the cpumask_t structure pointed to by
.Fa mask .
If the
.Fa pid
is zero,
then the pid of the calling process is used.
If the
.Fa tid
is less than zero,
then the first LWP of specified process is used.
.Sh RETURN VALUES
These system calls return \-1 on error and
0 upon successful completion.
.Sh ERRORS
The
.Fn lwp_setaffinity
and
.Fn lwp_getaffinity
system calls will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa name
parameter is outside the process's allocated address space.
.It Bq Er EINVAL
The
.Fa pid
parameter is negative.
.It Bq Er ESRCH
The LWP identified by the
.Fa pid
and the
.Fa tid
does not exist.
.It Bq Er EPERM
The
.Fa mask
does not contain a valid CPU.
.El
.Sh SEE ALSO
.Xr fork 2 ,
.Xr lwp_create 2 ,
.Xr rfork 2 ,
.Xr sched_getaffinity 2 ,
.Xr sched_setaffinity 2 ,
.Xr vfork 2 ,
.Xr pthread_create 3 ,
.Xr pthread_getaffinity_np 3 ,
.Xr pthread_setaffinity_np 3
.Sh HISTORY
The
.Fn lwp_setaffinity
and
.Fn lwp_getaffinity
functions first appeared in
.Dx 4.7 .