'\" t
.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH pthread_attr_setaffinity_np 3 2024-05-02 "Linux man-pages 6.9.1"
.SH NAME
pthread_attr_setaffinity_np, pthread_attr_getaffinity_np \- set/get
CPU affinity attribute in thread attributes object
.SH LIBRARY
POSIX threads library
.RI ( libpthread ", " \-lpthread )
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
.B #include <pthread.h>
.P
.BI "int pthread_attr_setaffinity_np(pthread_attr_t *" attr ,
.BI "                   size_t " cpusetsize ", const cpu_set_t *" cpuset );
.BI "int pthread_attr_getaffinity_np(const pthread_attr_t *" attr ,
.BI "                   size_t " cpusetsize ", cpu_set_t *" cpuset );
.fi
.SH DESCRIPTION
The
.BR pthread_attr_setaffinity_np ()
function
sets the CPU affinity mask attribute of the
thread attributes object referred to by
.I attr
to the value specified in
.IR cpuset .
This attribute determines the CPU affinity mask
of a thread created using the thread attributes object
.IR attr .
.P
The
.BR pthread_attr_getaffinity_np ()
function
returns the CPU affinity mask attribute of the thread attributes object
referred to by
.I attr
in the buffer pointed to by
.IR cpuset .
.P
The argument
.I cpusetsize
is the length (in bytes) of the buffer pointed to by
.IR cpuset .
Typically, this argument would be specified as
.IR sizeof(cpu_set_t) .
.P
For more details on CPU affinity masks, see
.BR sched_setaffinity (2).
For a description of a set of macros
that can be used to manipulate and inspect CPU sets, see
.BR CPU_SET (3).
.SH RETURN VALUE
On success, these functions return 0;
on error, they return a nonzero error number.
.SH ERRORS
.TP
.B EINVAL
.RB ( pthread_attr_setaffinity_np ())
.I cpuset
specified a CPU that was outside the set supported by the kernel.
(The kernel configuration option
.B CONFIG_NR_CPUS
defines the range of the set supported by the kernel data type
.\" cpumask_t
used to represent CPU sets.)
.\" The raw sched_getaffinity() system call returns the size (in bytes)
.\" of the cpumask_t type.
.TP
.B EINVAL
.RB ( pthread_attr_getaffinity_np ())
A CPU in the affinity mask of the thread attributes object referred to by
.I attr
lies outside the range specified by
.I cpusetsize
(i.e.,
.IR cpuset / cpusetsize
is too small).
.TP
.B ENOMEM
.RB ( pthread_attr_setaffinity_np ())
Could not allocate memory.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR pthread_attr_setaffinity_np (),
.BR pthread_attr_getaffinity_np ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
GNU;
hence the suffix "_np" (nonportable) in the names.
.SH HISTORY
glibc 2.3.4.
.SH NOTES
In glibc 2.3.3 only,
versions of these functions were provided that did not have a
.I cpusetsize
argument.
Instead the CPU set size given to the underlying system calls was always
.IR sizeof(cpu_set_t) .
.SH SEE ALSO
.BR sched_setaffinity (2),
.BR pthread_attr_init (3),
.BR pthread_setaffinity_np (3),
.BR cpuset (7),
.BR pthreads (7)