Technical Q&A's

PS 01 - Problem with Process Manager's WakeUpProcess Function (1-May-95)

Q I call the Process Manager's WakeUpProcess function from a completion routine to tell my application that my asynchronous request has completed. However, sometimes it seems that WakeUpProcess is ignored and my application doesn't wake up until the sleep value passed to WaitNextEvent expires. Does WakeUpProcess really work?

A You're running into a bug in the Process Manager that is fixed in System 7.1.2 (and later). Before System 7.1.2, WakeUpProcess doesn't do anything if the process being targeted is the active process and is executing the code in its event loop when WakeUpProcess is called. There are three things you can do to work around this problem.

First, in your completion routine, change the value of the sleep variable your application passes to WaitNextEvent to 0. That way, your next call to WaitNextEvent will give up as little time as possible.

Second, check the sleep variable just before you call WaitNextEvent and verify that it is zero (meaning your completion routine has been called). That should prevent WaitNextEvent from even being called when you don't need it to be called.

Third, for the sleep value you pass to WaitNextEvent while waiting for the call to complete, use a value that's small enough so that even if you hit the very small race window left by the first two suggestions above, your overall performance won't be affected very much.

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