PTHREAD_GETCONCURRENCY
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
pthread_getconcurrency,
pthread_setconcurrency
--- get and set the level of concurrency
SYNOPSIS
#include <pthread.h>
int pthread_getconcurrency(void);
int pthread_setconcurrency(int new_level);
DESCRIPTION
Unbound threads in a process may or may not be required to be
simultaneously active. By default, the threads implementation ensures
that a sufficient number of threads are active so that the process can
continue to make progress. While this conserves system resources, it
may not produce the most effective level of concurrency.
The
pthread_setconcurrency()
function allows an application to inform the threads implementation of
its desired concurrency level,
new_level.
The actual level of concurrency provided by the implementation as a
result of this function call is unspecified.
If
new_level
is zero, it causes the implementation to maintain the concurrency level
at its discretion as if
pthread_setconcurrency()
had never been called.
The
pthread_getconcurrency()
function shall return the value set by a previous call to the
pthread_setconcurrency()
function. If the
pthread_setconcurrency()
function was not previously called, this function shall return zero to
indicate that the implementation is maintaining the concurrency level.
A call to
pthread_setconcurrency()
shall inform the implementation of its desired concurrency level.
The implementation shall use this as a hint, not a requirement.
If an implementation does not support multiplexing of user threads on
top of several kernel-scheduled entities, the
pthread_setconcurrency()
and
pthread_getconcurrency()
functions are provided for source code compatibility but they shall
have no effect when called. To maintain the function semantics, the
new_level
parameter is saved when
pthread_setconcurrency()
is called so that a subsequent call to
pthread_getconcurrency()
shall return the same value.
RETURN VALUE
If successful, the
pthread_setconcurrency()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
The
pthread_getconcurrency()
function shall always return the concurrency level set by a previous
call to
pthread_setconcurrency().
If the
pthread_setconcurrency()
function has never been called,
pthread_getconcurrency()
shall return zero.
ERRORS
The
pthread_setconcurrency()
function shall fail if:
- EINVAL
-
The value specified by
new_level
is negative.
- EAGAIN
-
The value specified by
new_level
would cause a system resource to be exceeded.
The
pthread_setconcurrency()
function shall not return an error code of
[EINTR].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Application developers should note that an implementation can always
ignore any calls to
pthread_setconcurrency()
and return a constant for
pthread_getconcurrency().
For this reason, it is not recommended that portable applications
use this function.
RATIONALE
None.
FUTURE DIRECTIONS
These functions may be removed in a future version.
SEE ALSO
The Base Definitions volume of POSIX.1-2017,
<pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .