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)