Using an Event Callback to Process Driver Messages

To use an event callback, use the CreateEvent function to retrieve the handle of an event. In the call to the waveOutOpen function, specify CALLBACK_EVENT for the fdwOpen parameter. After calling the waveOutPrepareHeader function but before sending waveform-audio data to the device, create a nonsignaled event by calling the ResetEvent function, specifying the event handle retrieved by CreateEvent. Then, inside a loop that checks whether the WHDR_DONE bit is set in the dwFlags member of the WAVEHDR structure, call the WaitForSingleObject function, specifying as parameters the event handle and a time-out value of INFINITE.

Because event callbacks do not receive specific close, done, or open notifications, an application might have to check the status of the process it is waiting for after the event occurs. It is possible that a number of tasks could have been completed by the time WaitForSingleObject returns.