Using SetWaitableTimer

Posted on 1998-10-21
Last Modified: 2009-07-29
I am trying to use a one-shot timer, when I start the timer with the call SetWaitableTimer(timer, &DueTime, 0,func,NULL, false), DueTime.QuadPart = -10000, the timer starts ok but it expires periodically and I can not stop it with CancelWaitableTimer(). Also, I trap the timer expiration in the WaitForMultipleObjects() but the CALLBACK function is never executed automatically (I do reset the event after it is detected). Can Someone show me an example of how to start a one-shot timer for a duration of one second?. Thank You.
Question by:gtanoni
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Author Comment

ID: 1175711
Edited text of question

Author Comment

ID: 1175712
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Expert Comment

ID: 1175713
Are you using a waitable timer because you are using threads? If you are not using threads you should look at the multi-media timers (timeSetEvent and timeKillEvent funcitons)
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Accepted Solution

alexo earned 50 total points
ID: 1175714
First, you should create a manual reset timer thus:
    HAHDLE timer = CreateWaitableTimer(NULL, TRUE, NULL);

Then, start it thus:
    SetWaitableTimer(timer, &DueTime, 0, NULL, NULL, FALSE);

Note that a completion routine is not used (you either WaitForMultipleObjects() or use a completion routine, not both).  Also note the uppercase 'FALSE' (it is an int constant, not a bool).

Or, use a completion routhine thus:
    SetWaitableTimer(timer, &DueTime, 0, func, NULL, FALSE);

However, in order to allow the completion routhine to be executed by the thread, the thread *must* ne in an alertable wait state.  Entering an alertable wait state is done by calling one of the following APIs: MsgWaitForMultipleObjectsEx(), SignalObjectAndWait(), WaitForMultipleObjectsEx() or WaitForSingleObjectEx().  This state should be entered immediately after calling SetWaitableTimer().

Author Comment

ID: 1175715
I have tried the manual reset option on the CreateWaitableTimer call but I was not able to reset the event with ResetEvent(g_hEvents[TIMEOUT_EVENT]). So I set the CreateWaitableTimer flag to auto-reset and then it works fine. Thank you Alex for your answer.

Author Comment

ID: 1175716
rwilson: The reason why I need a waitable timer is because I am writing a service which implements a specific real-time protocol on a COM port and I do not want to implement a message pump (dispatch loop) that uses all the CPU. It is a multi-thread appplication.

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