Scheduler interface allows a thread some control over its
rate of execution.
Scheduler; PROCEDURE Yield();
If there are other threads ready to run, transfer control to one of them; otherwise continue with the current thread.
Implementation note: the exact semantics of
Yieldvaries widely from system to system. You shouldn't use it without consulting the detailed documentation for your implementation.
PROCEDURE DisableSwitching (); PROCEDURE EnableSwitching ();
Increment/decrement the counter that controls whether user-level thread switches may occur. The counter is initialized to zero. If the counter is greater than zero, switching is disabled. It's a checked runtime error to use any thread primitives (e.g. LOCK, Wait, Signal, Yield, ...) that would result in thread switches while switching is disabled.