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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.
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