A thread can also tell the system that it does not want to be schedulable for a certain amount of time. This is accomplished by calling Sleep:

VOID Sleep(DWORD dwMilliseconds);

This function causes the thread to suspend itself until dwMilliseconds have elapsed. There are a few important things to notice about Sleep:

• Calling Sleep allows the thread to voluntarily give up the remainder of its time slice.

• The system makes the thread not schedulable for approximately the number of milliseconds specified. That's right—if you tell the system you want to sleep for 100 milliseconds, you will sleep approximately that long but possibly several seconds or minutes more. Remember that Windows is not a real-time operating system. Your thread will probably wake up at the right time, but whether it does depends on what else is going on in the system.

• You can call Sleep and pass INFINITE for the dwMilliseconds parameter. This tells the system to never schedule the thread. This is not a useful thing to do. It is much better to have the thread exit and to recover its stack and kernel object.

• You can pass 0 to Sleep. This tells the system that the calling thread relinquishes the remainder of its time slice and forces the system to schedule another thread. However, the system can reschedule the thread that just called Sleep. This will happen if there are no more schedulable threads at the same priority.