A customer had a program which performed a long-running operation on its main UI thread. They wanted to display a “Please wait” dialog from a background thread, so they did something like this: void OnClick(HWND mainWindow) { PleaseWaitDialog dialog; dialog.Start(mainWindow); DoSomeReallyLongOperation(); The post Why can’t I create a “Please wait” dialog from a background thread to inform the user that the main UI thread is busy? appeared first on The Old New Thing....