Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!bbn.com!metasoft!alan
From: alan@metasoft.UUCP (Alan Epstein)
Newsgroups: comp.windows.x
Subject: Re: Debugging X11/Motif
Message-ID: <2150@metasoft.UUCP>
Date: 8 May 91 09:16:11 GMT
References: <259@picker.picker.com>
Distribution: na
Organization: Meta Software Corporation, Cambridge MA
Lines: 90

kobetitsch@picker.picker.com (harry kobetitsch) writes:
>I would like to know how to approach debugging X11/Motif applications...
>	X Protocol error: BadFont, invalid Font Parameter...
>Are there debugging guides out there for X11/Motif ?
>How does one interpret the above error message?

IMHO these protocol errors are just fine for server writers, but
don't help much with application level debugging. One easy method
of learning more about who did what wrong is to implement the
following:
1- Add an X protocol error handler in your application. This
   allows access to the error without terminating your application.

   Sometime after starting up your X connection, execute:
	XSetErrorHandler(My_XErrorHandler);
   My_XErrorHandler gets called instead of the normal error dumper,
   and you can breakpoint there for further information.

   My_XErrorHandler(), which is really a copy of the X error dumper,
   follows at the end of this message.

2- In order for My_XErrorHandler to be really useful, it is necessary
   to synchronize the display, probably after setting up the error
   routine. This is due to the asynchronicity of the protocol, wherein
   messages are not exchanged sequentially. Synching means that when
   the error handler is called, the backtrace will be accurate as
   far as who made the offending X call.

   call:
	XSynchronize((Display *) dpy, 1)
   'dpy' can be obtained via:
	TopLevel = XtInitialize(NULL, MyClassName, XtCommandLine,
				XtNumber(XtCommandLine),
				argcP, argv);
	dpy = XtDisplay(TopLevel);


Hope this helps.

-----------------------------
Alan Epstein
Meta Software Corp                   UUCP:  ...bbn!metasoft!alan
150 Cambridgepark Dr        Internet/ARPA:  alan%metasoft@bbn.com
Cambridge, MA 02140  USA
-----------------------------


___________________________ cut here _____________________________________


int My_XErrorHandler(Display * dpy, XErrorEvent * event)
{
#ifdef	DEBUG
    char buffer[BUFSIZ];
    char mesg[BUFSIZ];
    char number[32];
    char *mtype = "XlibMessage";
    FILE *fp = stderr;

    XGetErrorText(dpy, event->error_code, buffer, BUFSIZ);
    XGetErrorDatabaseText(dpy, mtype, "XError", "X Error", mesg, BUFSIZ);
    (void) fprintf(fp, "%s:  %s\n  ", mesg, buffer);
    XGetErrorDatabaseText(dpy, mtype, "MajorCode", "Request Major code %d", 
	mesg, BUFSIZ);
    (void) fprintf(fp, mesg, event->request_code);
    sprintf(number, "%d", event->request_code);
    XGetErrorDatabaseText(dpy, "XRequest", number, "", 	buffer, BUFSIZ);
    (void) fprintf(fp, " (%s)", buffer);
    fputs("\n  ", fp);
    XGetErrorDatabaseText(dpy, mtype, "MinorCode", "Request Minor code", 
	mesg, BUFSIZ);
    (void) fprintf(fp, mesg, event->minor_code);
    fputs("\n  ", fp);
    XGetErrorDatabaseText(dpy, mtype, "ResourceID", "ResourceID 0x%x",
	mesg, BUFSIZ);
    (void) fprintf(fp, mesg, event->resourceid);
    fputs("\n  ", fp);
    XGetErrorDatabaseText(dpy, mtype, "ErrorSerial", "Error Serial #%d", 
	mesg, BUFSIZ);
    (void) fprintf(fp, mesg, event->serial);
    fputs("\n  ", fp);
    XGetErrorDatabaseText(dpy, mtype, "CurrentSerial", "Current Serial #%d",
	mesg, BUFSIZ);
    (void) fprintf(fp, mesg, dpy->request);
    fputs("\n", fp);
#endif

    return 0;
    
}