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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PTHREAD_...CURRENCY(3P) POSIX Programmer's Manual PTHREAD_...CURRENCY(3P)
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.
pthread_getconcurrency, pthread_setconcurrency — get and set the
level of concurrency
#include <pthread.h>
int pthread_getconcurrency(void);
int pthread_setconcurrency(int new_level);
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.
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.
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.
None.
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.
None.
These functions may be removed in a future version.
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
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 .
IEEE/The Open Group 2017 PTHREAD_...CURRENCY(3P)
Pages that refer to this page: pthread.h(0p), pthread_setconcurrency(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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