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'\" t
.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH pthread_attr_setscope 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
pthread_attr_setscope, pthread_attr_getscope \- set/get contention scope
attribute in thread attributes object
.SH LIBRARY
POSIX threads library
.RI ( libpthread ", " \-lpthread )
.SH SYNOPSIS
.nf
.B #include <pthread.h>
.PP
.BI "int pthread_attr_setscope(pthread_attr_t *" attr ", int " scope );
.BI "int pthread_attr_getscope(const pthread_attr_t *restrict " attr ,
.BI " int *restrict " scope );
.fi
.SH DESCRIPTION
The
.BR pthread_attr_setscope ()
function sets the contention scope attribute of the
thread attributes object referred to by
.I attr
to the value specified in
.IR scope .
The contention scope attribute defines the set of threads
against which a thread competes for resources such as the CPU.
POSIX.1 specifies two possible values for
.IR scope :
.TP
.B PTHREAD_SCOPE_SYSTEM
The thread competes for resources with all other threads
in all processes on the system that are in the same scheduling
allocation domain (a group of one or more processors).
.B PTHREAD_SCOPE_SYSTEM
threads are scheduled relative to one another
according to their scheduling policy and priority.
.TP
.B PTHREAD_SCOPE_PROCESS
The thread competes for resources with all other threads
in the same process that were also created with the
.B PTHREAD_SCOPE_PROCESS
contention scope.
.B PTHREAD_SCOPE_PROCESS
threads are scheduled relative to other threads in the process
according to their scheduling policy and priority.
POSIX.1 leaves it unspecified how these threads contend
with other threads in other process on the system or
with other threads in the same process that
were created with the
.B PTHREAD_SCOPE_SYSTEM
contention scope.
.PP
POSIX.1 requires that an implementation support at least one of these
contention scopes.
Linux supports
.BR PTHREAD_SCOPE_SYSTEM ,
but not
.BR PTHREAD_SCOPE_PROCESS .
.PP
On systems that support multiple contention scopes, then,
in order for the parameter setting made by
.BR pthread_attr_setscope ()
to have effect when calling
.BR pthread_create (3),
the caller must use
.BR pthread_attr_setinheritsched (3)
to set the inherit-scheduler attribute of the attributes object
.I attr
to
.BR PTHREAD_EXPLICIT_SCHED .
.PP
The
.BR pthread_attr_getscope ()
function returns the contention scope attribute of the
thread attributes object referred to by
.I attr
in the buffer pointed to by
.IR scope .
.SH RETURN VALUE
On success, these functions return 0;
on error, they return a nonzero error number.
.SH ERRORS
.BR pthread_attr_setscope ()
can fail with the following errors:
.TP
.B EINVAL
An invalid value was specified in
.IR scope .
.TP
.B ENOTSUP
.I scope
specified the value
.BR PTHREAD_SCOPE_PROCESS ,
which is not supported on Linux.
.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_setscope (),
.BR pthread_attr_getscope ()
T} Thread safety MT-Safe
.TE
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH NOTES
The
.B PTHREAD_SCOPE_SYSTEM
contention scope typically indicates that a user-space thread is
bound directly to a single kernel-scheduling entity.
This is the case on Linux for the obsolete LinuxThreads implementation
and the modern NPTL implementation,
which are both 1:1 threading implementations.
.PP
POSIX.1 specifies that the default contention scope is
implementation-defined.
.SH SEE ALSO
.ad l
.nh
.BR pthread_attr_init (3),
.BR pthread_attr_setaffinity_np (3),
.BR pthread_attr_setinheritsched (3),
.BR pthread_attr_setschedparam (3),
.BR pthread_attr_setschedpolicy (3),
.BR pthread_create (3),
.BR pthreads (7)
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