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Technical Reference: Base Operating System and Extensions, Volume 1

pthread_getconcurrency or pthread_setconcurrency Subroutine


Gets or sets level of concurrency.


Threads Library (libthreads.a)


#include <pthread.h>

int pthread_getconcurrency (void); 
int pthread_setconcurrency (int new_level);


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 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 zero 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.

Return Value

If successful, the pthread_setconcurrency function returns zero. 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 zero.

Error Codes

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.

Implementation Specifics

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_getconcurrency and pthread_setconcurrency functions since their use may conflict with an applications use of these functions.

Related Information

The pthread.h file.

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