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Using Events with Asynchronous Calls

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[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Frequently, when using methods that are called asynchronously, you will want to halt further processing of your application until after the method completes processing. You can implement any technique you like to handle this situation. This section describes using an event to wait for asynchronous calls in the calling thread. This technique is frequently used with the Windows Media Format SDK, and is demonstrated in some of the sample applications.

The following list summarizes the use of events to wait for asynchronous calls.

  1. Create an event for use with your application by calling the CreateEvent function of the Platform SDK.
  2. When implementing the appropriate callbacks for your application, trap the messages for which you need to wait. In the message handling logic for the desired messages, signal the event by calling the SetEvent function of the Platform SDK.
  3. After calls to asynchronous events are made in your application, wait for the event to signal by calling the WaitForSingleObject function of the Platform SDK. If you are designing a Windows application, you should create a loop to check for Windows messages and include a call to WaitForSingleObject in the loop with a short wait time.

Using the Callback Methods