pthread_getconcurrency(3C) Standard C Library Functions pthread_getconcurrency(3C)
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_setconcur-
rency() 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(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
pthread_create(3C), pthread_attr_init(3C), attributes(5), standards(5)
SunOS 5.11 23 Mar 2005 pthread_getconcurrency(3C)