Hello, everyone. I'm trying to get my feet wet with some Linux/OSS programming by fixing some bugs in packages I use all the time. At the moment I have this X application (raw X, doesn't use GTK or Qt or anything like that) that spawns a subprocess when it starts. However, if you close the X application with anything other than the program's "Quit" button, like the X "Close" button in the window manager, the subprocess is not stopped and continues running ad infinitum, taking up a lot of resources in the process. I essentially want to catch the event of the user clicking the "X" button, so I can close it properly.
At first I naively thought that X would simply send a SIGTERM signal when the user closed the window. So I registered a SIGTERM handler in main():
Code:
1839 // Register SIGTERM callback
1840 struct sigaction sa;
1841 sa.sa_handler = handler;
1842 sa.sa_flags = 0;
1843 sigaction(SIGKILL, &sa, NULL);
1844 puts("Registered sigkill handler");
where "handler" is simply:
Code:
1865 void handler(int status) {
1866 puts("In the handler function");
1867 exit(EXIT_SUCCESS);
1868 }
If I use "kill -TERM", then the handler works, and I see the "In the handler function" output. But it doesn't get called at all when closing the X window, so I figured some other type of mechanism was being used. So I looked up the comp.windows.x FAQ and found something that looked promising:
Quote:
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Originally Posted by comp.windows.x FAQ Question 188
188) How do I catch the "close window" event to avoid "fatal IO error"?
Several windows managers offer a function such as f.kill or f.delete
which sends a message to the application that it should delete its window;
this is usually interpreted as a shutdown message.
The application needs to catch the WM_DELETE_WINDOW client message.
There is a good example in the xcalc sources in X11R5.
Motif-based applications should in addition set the resource
XmNdeleteResponse on the top-level shell to XmDO_NOTHING, whether they are
using the Motif window manager or not.
If the application doesn't handle this message the window manager may
wind up calling XKillClient, which disconnects the client from the display and
typically gives an Xlib error along the lines of "fatal IO error 32 (Broken
pipe)".
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However, I'm not sure what "catch the WM_DELETE_WINDOW client message" entails, and Google'ing hasn't helped me. I checked the source of xcalc as they said, but I found nothing helpful there. The only reference to WM_DELETE_WINDOW was here:
Code:
146 dpy = XtDisplay(toplevel);
147 wm_delete_window = XInternAtom(dpy, "WM_DELETE_WINDOW", False);
148 (void) XSetWMProtocols(dpy, XtWindow(toplevel), &wm_delete_window, 1);
But I don't really understand what that does.
I'm hoping one of the gurus here can help me out
I have little experience with X and C, so please use simple language
. Thanks in advance!
