PTHREAD_GETCONCURRENCY(P) POSIX Programmer's Manual PTHREAD_GETCONCURRENCY(P)
pthread_getconcurrency, pthread_setconcurrency - get and set the level of concurrency
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 imple-
mentation 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 previ-
ously called, this function shall return zero to indicate that the implementation is main-
taining the concurrency level.
A call to pthread_setconcurrency() shall inform the implementation of its desired concur-
rency 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 ker-
nel-scheduled entities, the pthread_setconcurrency() and pthread_getconcurrency() func-
tions 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 specific by new_level would cause a system resource to be exceeded.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Use of these functions changes the state of the underlying concurrency upon which the
application depends. Library developers are advised to not use the pthread_getconcur-
rency() and pthread_setconcurrency() functions since their use may conflict with an appli-
cations use of these functions.
The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_GETCONCURRENCY(P)