What makes a process appear as Not responding in Windows?

What is it exactly that "triggers" Windows to mark a process as Not responding in the Task Manager and Resource开发者_C百科 Monitor?

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The API behind this is IsHungAppWindow. Basically, if the application has not pumped a message within 5 seconds it can be marked as not responding.

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If a process does not collect Windows messages from its queue using the GetMessage function or something related, it will be tagged as "not responding" -- because it is not responding to user interface events.

This does not necessarily mean that the application is actually hung -- it may just be too busy to pay attention to the user.

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Basically, it get's it self into a state where the program does not return to a point where it can process it's message queue.

Usually, this is either a loop that doesn't end or a blocking operation, such as reading from a socket, etc.

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The fact that they don't empty their message queue, by polling it GetMessge API and the like.