signal when user kills process?

Question

I overloaded the 6 signals listed on this site http://www.cplusplus.com/reference/clibrary/csignal/signal.html

Then i ran my app (double click not ran through IDE) and tried 1) end task 2) X on topright and 3) kill process. I expected the first two to cause some kind of signal (i am on XP) but alas i got nothing. Am i not allowed to open files to write into when a signal occurs? i am guessing i am (SIGSEGV allowed me).

When firefox crashes or when i kill it, it remembers what pages i was. Does it log the address everytime i click a page or does it do that on a signal/crash?

my main question is what signal can i use to catch kill process

Answer 1

Win32 does not provide an option to intercept your program being killed with TerminateProcess (which is what will happen when you "End Task" from Task Manager or click on the [X]).

You can catch the SIGSEGV signal because the C runtime library provides an emulation of this signal when running on Windows. When your program causes a Windows access violation (exception 0xC0000005), the runtime library has the option to catch that and simulate a Unix style SIGSEGV for you. This is, however, not the best way to handle such an exception. If you are writing a Win32 program, you shouldn't generally try to use Unix style services.

Answer 2

You can catch runtime error like an access violation if you override the default exception handler calling SetUnhandledExceptionFilter (this is a win32 function and as such doesn't rely on C library emulation). This is the method can used to provide "minidumps" when a program crashes.

But this exception handler will not be called when you normally close your application, or when your application is closed from Task manager. In the last case windows is calling TerminateProcess, is not a clean shutdown but it is forcing your program to terminate.

I'm not aware of which is the implementation used by Firefox, but to save the current tabs open is likely to have a timer running, and each time it is run it save the history to a file and some kind of dirty mark.

Other more complex solutions to detect when a program is closed (implemented by antivirus and similar programs) is to have two unrelated programs running, each checking that the other is still running, and if one detect the other was closed the run it again.

Answer 3

Windows apps are either console apps or GUI apps. Console apps tend to get WM_CLOSE, console apps CTRL_CLOSE_EVENT. Neither are signals; neither would be sent if your app is ended via TerminateProcess().

If you want to store where you were, use a memory-mapped file and update that on every action. When your process exits, the dirty page in memory is written back to file by the OS, possibly at other moments too. This solution allows the OS to manage disk I/O for you, and it's in a better position to do so.