sched_yield - Signals scheduler a willingness to yield to another thread.
DECthreads POSIX 1003.1c Library (libpthread.so)
Interfaces documented on this reference page conform to industry standards as follows:
IEEE Std 1003.1c-1995, POSIX System Application Program Interface
This routine forces the running thread to relinquish the processor until it again becomes the head of its thread list. This routine notifies the thread scheduler that the current thread is willing to release its processor to other threads of equivalent or greater scheduling precedence. (A thread generally will release its processor to a thread of a greater scheduling precedence without calling this routine.) If no other threads of equivalent or greater scheduling precedence are ready to execute, 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 sched_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 sched_yield, other threads can be given the opportunity to run when the resources are free. This can sometimes improve 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) that 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 which will increase overhead and 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.
Functions: pthread_attr_setschedparam(3), pthread_setschedparam(3)
Manuals: Guide to DECthreads and Programmer's Guide