Yield (YIELD)

Description:   The dispatching algorithm is run. If another thread of equal or higher priority is eligible to run, then a thread is chosen and dispatched. Otherwise, the current thread resumes execution.

Usage Notes

The yield() function is a common technique used on other platforms to serialize on a resource or to allow other threads of equal or higher priority to execute before the current thread begins execution of a long running function.

• Serialization of a resource

  A "spin" lock is a high speed synchronization primitive in which the application "loops" on the setting of a variable which is used to synchronize access to a resource. A typical application implementation of a spin lock might be:

  1. Compare and swap on a variable that synchronizes access to a resource.
  2. If not available and first time in loop, invoke the yield() function.
  3. Otherwise if not the first time in loop, wait for a small time quantum. This time quantum is incremented each time through the loop.
  4. Loop back to the compare and swap statement.
• Allow threads of equal or higher priority to run

  The yield() function allows a thread to immediately relinquish control to a thread of equal or higher priority. On other platforms, this is done because the kernel can not (usually) be preempted. On i5/OS^®, the duration of time another thread of equal or higher priority may be prevented from executing until the current thread reaches time-slice end is considered to be very large, especially considering the processing speeds of current machines.

Authorization Required

• None

Lock Enforcement

• None

Exceptions

• None