Running a Windows program and detect when it ends with C++

Question

Suppose I run an application, after some time this app will get closed by user. Is it possible to find out when the program exits? Can I get it\'s process id when I run that

Answer 1

CreateProcess and WaitForSingleObject is the simple way to achieve this: you get the process handle from CreateProcess, then wait for it with WFSO, not forgetting to close any handles you use. But wait... there's a problem. The problem is that - for GUI processes - both processes can hang. Why?

The problem arises because your application has a window but isn't pumping messages. If the spawned application invokes SendMessage with one of the broadcast targets (HWND_BROADCAST or HWND_TOPMOST), then the SendMessage won't return to the new application until all applications have handled the message - but your app can't handle the message because it isn't pumping messages.... so the new app locks up, so your wait never succeeds.... DEADLOCK.

If you have absolute control over the spawned application, then there are measures you can take, such as using SendMessageTimeout rather than SendMessage (e.g. for DDE initiations, if anybody is still using that). But there are situations which cause implicit SendMessage broadcasts over which you have no control, such as using the SetSysColors API for instance.

The only safe ways round this are (a) split off the Wait into a separate thread, (b) use a timeout on the Wait and use PeekMessage in your Wait loop to ensure that you pump messages, (c) use the MsgWaitForMultipleObjects API instead of WaitForSingleObject.