Asynchronous Timers

DosSleep is useful for temporarily suspending a thread but is much less useful for timing. Typically, an application carries out part of its task and then waits an interval. If the execution time varies (as it will if the application runs on different hardware), the overall interval varies. In these situations, asynchronous timers provide greater precision than DosSleep.

OS/2 supports two types of asynchronous timers, single-interval (one-shot) and repeated. DosAsyncTimer starts a single-interval timer. During the timing interval, the application can carry out other tasks. The system posts an event semaphore when the timing interval elapses. The application can reset the semaphore with DosResetEventSem before starting the timer. DosAsyncTimer yields a more accurate timing interval than DosSleep because the interval is independent of the execution time.

DosStartTimer starts a repeated timer. The system posts an event semaphore each time the interval expires. The application can reset the semaphore before starting the timer and after each posting. When the application resets the semaphore with DosResetEventSem, it can check the cPosts value to determine how many times the semaphore has been posted. If the semaphore has been posted more than once, the application has missed a timer interval.

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