Writing a Timer Callback Function

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[The feature associated with this page, Multimedia Timers, is a legacy feature. It has been superseded by Multimedia Class Scheduler Service. Multimedia Class Scheduler Service has been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Multimedia Class Scheduler Service instead of Multimedia Timers, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Note

This topic describes an obsolete function. New applications should use the CreateTimerQueueTimer function to create timers.

 

The following callback function, OneShotTimer, invalidates the identifier for the single timer event and calls a timer routine to handle the application-specific tasks. For more information, see TimeProc.

void CALLBACK OneShotTimer(UINT wTimerID, UINT msg, 
    DWORD dwUser, DWORD dw1, DWORD dw2) 
{ 
    NPSEQ npSeq;             // pointer to sequencer data 
    npSeq = (NPSEQ)dwUser;
    npSeq->wTimerID = 0;     // invalidate timer ID (no longer in use)
    TimerRoutine(npSeq);     // handle tasks 
}

Using Multimedia Timers