Determine priority of a window message

Question

Is there any way to programmatically check the priority of a window messages in its message queue?

For example: Some of window messages, WM_PAINT and

Answer 1

That's just not how it works, Windows messages don't have a priority attached. It is mostly determined by how the message is generated. A message loop dispatches messages in this order:

• first any messages generated with SendMessage() are dispatched in the order in which the calls were made
• next, any messages generated with PostMessage() and stored in the message queue, in queue order
• next, any messages that are synthesized from the window state. WM_TIMER, WM_PAINT and WM_MOUSEMOVE fit this category.

The 'synthesized from the window state' clause is what makes WM_PAINT and WM_TIMER appear to have a low priority. And why moving the mouse rapidly doesn't flood the message queue with mouse messages. That is however not exclusive, you can for example call UpdateWindow() to force a WM_PAINT message to be sent, making it being dispatched with a 'high priority'.

Answer 2

The order is defined in GetMessage / PeekMessage documentation:

If no filter is specified, messages are processed in the following order:

• Sent messages
• Posted messages
• Input (hardware) messages and system internal events
• Sent messages (again)
• WM_PAINT messages
• WM_TIMER messages