Suspending Thread Execution

A thread can suspend and resume the execution of another thread using the SuspendThread and ResumeThread functions. While a thread is suspended, it is not scheduled for time on the processor.

The SuspendThread function is not particularly useful for synchronization because it does not control the point in the code at which the thread's execution is suspended. However, you might want to suspend a thread in a situation where you are waiting for user input that could cancel the work the thread is performing. If the user input cancels the work, have the thread exit; otherwise, call ResumeThread.

If a thread is created in a suspended state (with the CREATE_SUSPENDED flag), it does not begin to execute until another thread calls ResumeThread with a handle to the suspended thread. This can be useful for initializing the thread's state before it begins to execute. See Using a Multithreaded Multiple Document Interface Application for an example that uses this method to modify the thread's priority before it can run. Suspending a thread at creation can be useful for one-time synchronization, because this ensures that the suspended thread will execute the starting point of its code when you call ResumeThread.

A thread can temporarily yield its execution for a specified interval by calling the Sleep or SleepEx functions This is useful particularly in cases where the thread responds to user interaction, because it can delay execution long enough to allow users to observe the results of their actions. During the sleep interval, the thread is not scheduled for time on the processor.

The SwitchToThread function is similar to Sleep and SleepEx, except that you cannot specify the interval. SwitchToThread allows the thread to give up its time slice.