the thread continues. This routine can allow knowledge of the details of an application to be used to improve its performance. If a thread does not call tis_yield(), other threads may be given the opportunity to run at arbitrary points (possibly even when the interrupted thread holds a required resource). By making strategic calls to tis_ yield(), other threads can be given the opportunity to run when the resources are free. This improves performance by reducing contention for the resource. As a general guideline, consider calling this routine after a thread has released a resource (such as a mutex) which is heavily contended for by other threads. This can be especially important if the program is running on a uniprocessor machine, or if the thread acquires and releases the resource inside a tight loop. Use this routine carefully and sparingly, because misuse can cause unnecessary context switching that will increase overhead and actually degrade performance. For example, it is counter- productive for a thread to yield while it holds a resource that the threads to which it is yielding will need. Likewise, it is pointless to yield unless there is likely to be another thread that is ready to run.

33.4  –  Return Values

    If an error condition occurs, this routine returns an integer
    value indicating the type of error. Possible return values are as
    follows:

    Return      Description

    0           Successful completion.
    [ENOSYS]    The routine tis_yield()  is not supported by this
                implementation.