Microsoft KB Archive/40669

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HOWTO: Post Frequent Messages Within an Application

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Q40669

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The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK)
 * Microsoft Windows Software Development Kit (SDK)

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SUMMARY
The object-oriented nature of Windows programming can create a situation in which an application posts a message to itself. When such an application is designed, care must be taken to avoid posting messages so frequently that system messages to the application are not processed. This article discusses two methods of using the PeekMessage function to combat this situation.

MORE INFORMATION
In the first method, a PeekMessage loop is used to check for system messages to the application. If none are pending, the SendMessage function is used from within the PeekMessage loop to send a message to the appropriate window. The following code demonstrates this technique:

  while (fProcessing) {       if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {            if (msg.message == WM_QUIT) break; /* Process system messages. */             }        else {            /* Perform other processing. */             ...             /* Send WM_USER message to window procedure. */             SendMessage(hWnd, WM_USER, wParam, lParam); }       } In the second method, two PeekMessage loops are used, one to look for system messages and one to look for application messages. PostMessage can be used from anywhere in the application to send the messages to the appropriate window. The following code demonstrates this technique:

  while (fProcessing) {       if (PeekMessage(&msg, NULL, 0, WM_USER-1, PM_REMOVE)) {            if (msg.message == WM_QUIT) break; /* Process system messages. */             }        else if (PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_REMOVE)) /* Process application messages. */        } An application should use a PeekMessage loop for as little time as possible. To be compatible with battery-powered computers and to optimize system performance, every Windows-based application should inform Windows that it is idle as soon and as often as possible. An application is idle when the GetMessage or WaitMessage function is called and no messages are waiting in the application's message queue.

Additional query words:

Keywords : kbOSWinNT kbOSWin2000 kbSDKWin32 kbGrpDSUser kbOSWin kbWndw kbWndwMsg kbWndwProc

Issue type : kbhowto

Technology : kbWin32SDKSearch kbAudDeveloper kbSDKSearch kbWin32sSearch kbWinSDKSearch