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DispatchMessage Implementation Notes

• DispatchMessage takes one argument - a pointer to an object of type MSG whose members hold complete information about the message. This includes a handle to the window for which the message is meant.
• This handle will always have a valid value except when the message has been posted through a call to PostThreadMessage. Conversely, whenever this handle has a valid value (i.e., it is not NULL) we can assume that its for a window that already exists.
• If so we can safely derive that the function retrieves the pointer to the message handling function (from the WNDCLASS object registered with the system through a call to RegisterClass) using this handle and invokes it.
• Regardless of the actual message that is generated, in order for it to be placed in the thread's message queue, a call to PostMessage has to be made (SendMessage directly invokes the message processing function). The handle to the window for which the message is meant is supplied as a paramter to it. This message is ultimately retrieved from the queue through a call to GetMessage and delegated to DispatchMessage.
• This is understandable. But in the case that the message has been posted to the queue through a call to PostThreadMessage, the handle to the window in the MSG structure will be NULL. Therefore, DispatchMessage cannot retrieve a pointer to the message processing function. This begs a rather obvious question - to whom or what pray will DispatchMessage dispatch the message? The answer is, the message will not be dispatched anywhere! It will simply diappear into oblivion!

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