Q89738: INFO: Handling WM_QUIT While Not in Primary GetMessage() Loop

Article: Q89738
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly kbSDKPlatform kbGrpDSUser kbWndw kbWndwMsg
Last Modified: 12-JUN-1999

3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

An application can terminate while in a message loop that is different from the
primary GetMessage() loop. If this secondary message loop retrieves the WM_QUIT
message from the message queue, the message must be reposted so that the primary
GetMessage() loop can exit.

MORE INFORMATION
================

An application can get into a secondary message loop that is different from the
primary GetMessage() loop in order to track drag messages, yield periodically
during lengthy processing, and so on. The user may be able to terminate the
application while the secondary message loop is being used to retrieve messages
from the message queue.

If the GetMessage()/PeekMessage() call used in the secondary loop specifies a
message filter that does not include WM_QUIT, WM_QUIT will not be retrieved from
the message queue. When the loop terminates, control will be returned to the
primary GetMessage() loop, which retrieves the WM_QUIT message.

If the GetMessage()/PeekMessage() call in the secondary loop retrieves all
messages or specifies a message filter that includes the WM_QUIT message, the
WM_QUIT message that is retrieved must be reposted and control must be returned
to the primary message loop. The primary message loop will then retrieve the
reposted WM_QUIT message and exit.

     while (bNotDone)
     {

     // Secondary message loop
     while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
     {
        if (msg.message == WM_QUIT)
        {
           // Repost the QUIT message so that it will be retrieved by the
           // primary GetMessage() loop.
           PostQuitMessage(msg.wParam);
           return FALSE;
        }
        // Pre-process message if required (TranslateAccelerator etc.)
        TranslateMessage(&msg);
        DispatchMessage(&msg);
        :
        :
     }
     :

  }

The primary message loop will not exit if the secondary message loop does not
repost the WM_QUIT message. Consequently, the application will remain in memory
even though all its windows are destroyed.

An alternative solution is to prevent the user from terminating the application
while the application is in the secondary message loop.

Additional query words: 3.00 3.10 close

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Keywords          : kb16bitonly kbSDKPlatform kbGrpDSUser kbWndw kbWndwMsg 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

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