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The system offers a function called SwitchToThread that allows another schedulable thread to run if one exists:

 BOOL SwitchToThread(); 

When you call this function, the system checks to see whether there is a thread that is being starved of CPU time. If no thread is starving, SwitchToThread returns immediately. If there is a starving thread, SwitchToThread schedules that thread (which might have a lower priority than the thread calling SwitchToThread). The starving thread is allowed to run for one time quantum and then the system scheduler operates as usual.

This function allows a thread that wants a resource to force a lower-priority thread that might currently own the resource to relinquish the resource. If no other thread can run when SwitchToThread is called, the function returns FALSE; otherwise, it returns a nonzero value.

Calling SwitchToThread is similar to calling Sleep and passing it a timeout of 0 milliseconds. The difference is that SwitchToThread allows lower-priority threads to execute. Sleep reschedules the calling thread immediately even if lower-priority threads are being starved.

Windows 98

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Windows 98 does not have a useful implementation for this function.