A thought i had the other day... When you shutdown windows, all programs close, but how do they know to close?

My first thought was that GetMessage would return WM_QUIT, in which case apps would close themselves.

Then not long after, i realized that method would in effect just terminate applications, not giving them the chance the close file handles and stuff in the normal way - on receive of WM_DESTROY, or whatever...

I am out of ideas, and don't exactly know what to test to find out - if i try to shutdown, everything will close and i wont see my results...

So does anyone know how applications know to close when windows is shutting down?


This is not an urgent thing or anything, i just couldn't think of a way it could be done Probably something really simple which I didn't think of

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I think windows just sends WM_CLOSE to apps, and then terminates those which don't respond in time.

Windows also sends the WM_ENDSESSION message. An application should process the message if it needs to do any special actions during shutdown.

ok... but what about processes with no message loop? would they just terminate after so many seconds?

Apps without message loops and apps that are not responding to the WM_CLOSE message cannot be nicely closed. Windows will wait up to 30 seconds for the app to close, it will also display a window allowing the user to "End Now" without waiting. In either case (the user clicks "End Now" or 30 seconds have passed) Windows will forcibly terminate the process.

The closing of a process quite simple. a process just needs to call the API TerminateProcess. it's the programs responsibility to determine how this happens i usually let windows do it for me by returning from my program to the system where the kernel calls it for me.

As for messages it is usually a good idea to direct WM_CLOSE code that will eventually call TerminateProcess, after you have done all of your cleanup of course.

If you want to see this in action try using my little KILL app, I've attached the source. to use this drag from it's the windows grey over any window window and it will die instantly no wait, no saving, no messages. Warning this will kill explorer and the desktop too. I did code an exception so it wont kill it's self.

Warning the new version of AntiVir seems to detect this as a virus which is why i didn't include the binary. if you are worried about it then just check the source.

Also note that some frozen windows will be treated as though they are the desktop, I personally consider this a flaw in windows as i have done some testing and found that this error is a result of what appears to be a windows bug.

I am not responsible for any crashes or data loss due to use of this program. this is a test model and not to be considered a tool. The Icon and Cursor are My art work and you may not use them with out my permission (If you want to use them just ask, I don't intend to be a hard ass about people using them i just want credit if you place them in your app)

Anyway in answer to your question, windows just loops through all the process handles and terminates them one at a time. of course it does give them a chance to close first usually a few seconds, you can change that value in the registry to let it wait longer or close faster)

Just to note that calling ExitProcess is preferred to TerminateProcess. The Exit version allows the process to shut down cleanly whereas the Terminate version will abruptly stop the process uncleanly.

from msdn


This is why i use TerminateProcess it's a guaranteed kill, while exit process may be cleaner but it isn't as effective. the truely best result would be to call ExitProcess and if the process still exists one or two seconds later to call TerminateProcess.