PTHREAD_GETCONCURRENCY(3C) Standard C Library Functions

NAME

pthread_getconcurrency, pthread_setconcurrency - get or set level of
concurrency

SYNOPSIS

cc -mt [ flag... ] file... -lpthread [ library... ]
#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 0, it causes the implementation to maintain the
concurrency level at its discretion as if pthread_setconcurrency() was
never called.


The pthread_getconcurrency() function returns the value set by a
previous call to the pthread_setconcurrency() function. If the
pthread_setconcurrency() function was not previously called, this
function returns 0 to indicate that the implementation is maintaining
the concurrency level.


When an application calls pthread_setconcurrency() it is informing the
implementation of its desired concurrency level. The implementation uses
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 will be provided for source code
compatibility but they will have no effect when called. To maintain the
function semantics, the new_level parameter will be saved when
pthread_setconcurrency() is called so that a subsequent call to
pthread_getconcurrency() returns the same value.

RETURN VALUES

If successful, the pthread_setconcurrency() function returns 0.
Otherwise, an error number is returned to indicate the error.


The pthread_getconcurrency() function always returns the concurrency
level set by a previous call to pthread_setconcurrency(). If the
pthread_setconcurrency() function has never been called,
pthread_getconcurrency() returns 0.

ERRORS

The pthread_setconcurrency() function will 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.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

pthread_attr_init(3C), pthread_create(3C), attributes(7), standards(7)


March 23, 2005 PTHREAD_GETCONCURRENCY(3C)