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From: news@bbn.com (News system owner ID)
Newsgroups: comp.windows.x
Subject: Re: "Close" window operation under mwm (Motif Window Manager)...
Keywords: mwm, error, close, window manager
Message-ID: <64235@bbn.BBN.COM>
Date: 17 May 91 04:37:46 GMT
References: <1991May5.070402.2985@cs.ucla.edu>
Reply-To: rnewman@bbn.com (Ron Newman)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 63


william@oahu.cs.ucla.edu (William Cheng) writes:

|> Under mwm (Motif Window Manager), if an application is CLOSED by
|> selecting the "Close" entry in the popup menu which is generated
|> by clicking the button on the left top portion of the window,
|> an XIO error often occures with the following messages:
|> 
|> XIO:  fatal IO error 32 (Broken pipe) on X server "rye:0.0"
|>       after 445 requests (89 known processed) with 0 events remaining.
|>       The connection was probably broken by a server shutdown or KillClient.
|> 
|> This happens with many applications (bitmap, xdvi, idraw, xfd, xlogo...)
|> but not with xloadimage, xclock, xload.  Apparently, any application that
|> has more than one window will get the error message.

The "Close" item in the Motif Window Manager menu invokes mwm's "f.kill"
function, which does one of two things:

    1) Sends a ClientMessage event to the window, with 
           message_type = WM_PROTOCOLS atom
           format = 32
           data.l[0] = WM_DELETE_WINDOW atom

or
 
    2) calls XKillClient on the window, which rudely breaks
          its application's connection to the X server.

If the application has registered for the WM_DELETE_WINDOW protocol, mwm
(or any other ICCCM-compliant window manager) will do the first, giving the
application a chance to shut down gracefully (or, for that matter, to 
refuse to shut down).   xclock, for example, contains this code to
register for the protocol

    wm_delete_window = XInternAtom (XtDisplay(toplevel), "WM_DELETE_WINDOW",
                                    False);
    (void) XSetWMProtocols (XtDisplay(toplevel), XtWindow(toplevel),
                            &wm_delete_window, 1);

and this code to handle the resulting ClientMessage event:

    XtOverrideTranslations(toplevel,
                    XtParseTranslationTable ("<Message>WM_PROTOCOLS: quit()"));

along with a quit() action procedure that calls XCloseDisplay() and exit().

If the application hasn't registered for WM_DELETE_WINDOW,
mwm does the second action (XKillClient).  The application will die with an
XIOError the next time it tries to read from the (now closed) X
socket.  That's what you're seeing.  Many of MIT's officially distributed
X clients don't register for WM_DELETE_WINDOW.

For more information, look at sections 4.1.2.7, 4.2.8, and (especially)
5.2.2 of the Inter-Client Communication Conventions Manual (ICCCM).  Also
section 14.3.4 ("MWM Functions") of the OSF/Motif Programmer's Guide, 
which describes the "f.kill" function.

Note that the Open Look window manager calls this same function "Quit"
(their "Close" is more like Motif's "Minimize").

/Ron Newman	rnewman@bbn.com
Ron Newman		rnewman@bbn.com