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Problem with the message pump hanging

Posted on 1997-08-29
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Last Modified: 2013-12-03
I have a very strange problem. I am working with an application that
uses many different threads. At some point I seem to get into a
situation where there are no threads to pump the message queue. The code
in question create an event and posts a WM_USER style message to the
window queue and then does a WaitForSingleObject(). The message pump is
supposed to see the message and post the event to cause the wait to
finish. The problem appears to be that the thread that is supposed to be
pumping is the one waiting. I tried using WaitForMultipleObjects() and
dispatching the messages myself but that also doesn't seem to work.
I am looking for any other clues that prople might be able to give me.

The purpose of this logic is to insure that the message queue is empty
before killing the window. The processing must be synchonous. I don't think I can allow the window to
go down asynchronously
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Question by:sasjaa
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3 Comments
 
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Expert Comment

by:vinniew
ID: 1405120
You shouldn't do it like that.  It's much easier to control if you use a global flag (bool) variable to control things like that.  As for checking the queue before you 'kill' the process, I think you should use Mutexes (see CreateMutex) instead of events.  The event processing is what's causing problems.  You can use mutexes in the same way, but they work inside the main process.

In any case, I can't be sure about this solution without seeing code or without a general outline of what's happening, so post more if you need more.
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Author Comment

by:sasjaa
ID: 1405121
I don't see how a Mutex can help. A window destroy request comes in and we need to make sure that there are no pending messages in the queue for this window before we delete the object. Microsoft documentation clearly states that a CEvent should be used if we must wait for something else to happen before continuing. The problem is that we are waiting on messages and there seems to be nothing to process the messages.
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Accepted Solution

by:
vinniew earned 400 total points
ID: 1405122
You could start up another message 'pump within a pump' to handle the wm_destroy message.  Use the while.. peekmessage.. sendmessage... loop in the handler for wm_destroy.  That would definitely empty the queue.

V
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