PRB: Oleaut32 Hidden Window Blocks Apps Broadcasting Messages

   Date        Time    Version      Size      File name     
   -------------------------------------------------------
   05/29/2001  06:23p  2.40.4518.0  143,632   Asycfilt.dll
   05/29/2001  06:23p  2.40.4518.0  626,960   Oleaut32.dll
   05/29/2001  06:23p  5.0.4518.0   164,112   Olepro32.dll

				

MORE INFORMATION

Steps to Reproduce Behavior

Use the following code to develop a console application:

Sample Code

    #define _WIN32_DCOM
    #include <windows.h>

    void main()
    {
   CoInitializeEx(NULL, COINIT_MULTITHREADED);
   VARIANT var,var1;
   VariantInit(&var);
   VariantInit(&var1);
   BSTR str = SysAllocString(L"Test");
   var.vt = VT_BSTR;
   var.bstrVal = str;
   VariantChangeType(&var, &var, 0, VT_I2);
   VariantClear(&var);
   VariantClear(&var1);
   while (1)
   {
      ;
   }
   CoUninitialize();

    }
				

Run this application. Run another application that broadcasts a message (for example, double click a .doc icon on the desktop). A message is broadcast to all the top-level windows that are using either SendMessage or a non-blocking variation of the SendMessage API (such as SendMessageTimeout). The broadcasting application is either blocked (hung) indefinitely or hung for the period of time it takes the call to timeout.

One work around for the problem is to create a secondary thread from the primary thread. After you have done this, call an automation method on the secondary thread's procedure (the secondary thread will create the hidden top-level window). Create a message loop to process the messages in the secondary thread. After everything is finished, close the secondary thread from the primary thread. Since there is a message pump in the secondary thread, any broadcasted message will be processed.

Sample Code

   #define _WIN32_DCOM
   #include <windows.h>

   HANDLE g_EventHandle;

   DWORD WINAPI SecondaryThread(LPVOID pInputParam)
   {

      HRESULT hr = S_OK;
      // Initialize COM with Mutithreaded.
      hr = CoInitializeEx(NULL,COINIT_MULTITHREADED);

      VARIANT var, var1;

      VariantInit(&var);
      VariantInit(&;var1);
      BSTR str = SysAllocString(L"Test");
      var.vt = VT_BSTR;
      var.bstrVal = str;

      // This will create a hidden window in this thread.
      hr = VariantChangeType(&var, &var, 0, VT_I2);

      // Set the global event.
      SetEvent(g_EventHandle);

      VariantClear(&var);
      VariantClear(&var1);

      MSG msg;

       // msg-pump.
       while (GetMessage(&msg, NULL, 0, 0))
       {
            // This was the message -- time to work.
            if ( msg.message == WM_USER+1)
            {
                // When done:
      break;
        }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        CoUninitialize();
        return 0;
   }

   void main()
   {

      DWORD dwThreadID;
      HANDLE hThread;

      // Create a global Event.
      g_EventHandle = CreateEvent(NULL, FALSE, FALSE, NULL);
      // Spin the secondary thread.
      hThread = CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)
                             SecondaryThread,0,0,&dwThreadID);
      DWORD ret;
      // Wait until the event is set in the secondary thread.
      ret = WaitForSingleObject(g_EventHandle, INFINITE);

      CoInitializeEx(NULL, COINIT_MULTITHREADED);
       // Any other code.
       while (1)
      {
         ;
      }
      CoUninitialize();

      // Clean up the secondary thread.
      PostThreadMessage(dwThreadID,WM_USER+1,0,0);
      WaitForSingleObject(hThread, INFINITE);
      CloseHandle(hThread);
   }