Stephen J. Turnbull <[email protected]> added the comment:
Re: msg124528
Yes, XEmacs installs a signal handler on what are normally fatal errors. (I
don't know about GNU Emacs but they probably do too.)
The handler has two functions: to display a Lisp backtrace and to output a
message explaining how to report bugs (even including a brief introduction to
the "bt" command in gdb. ;-)
I personally have never found the Lisp backtrace useful, except that it can be
used as a bug signature of sorts ("oh, I think I've seen this one before...").
However, I suspect this is mostly because in Emacs Lisp very often you don't
have the name of the function in the backtrace, only a compiled code object.
So in many cases it's almost no help in localizing the fault. Victor's patch
does a lot better on this than XEmacs can, I suspect.
The bug reporting message, OTOH, has been useful to us for the reasons people
give for wanting the handler installed by default. We get more and better bug
reports, often including C backtraces, from people who have never participated
directly in XEmacs development before. (It also once served the function of
inhibiting people from sending us core files. Fortunately, I don't think that
happens much any more. :-) Occasionally a user will be all proud of themselves
because "I never used gdb before," so I'm pretty sure that message is effective.
Quite frequently we see the handler itself crash if there was memory
corruption, but certainly it gives useful output well over half the time. So I
want to back up Victor on those aspects.
Finally, although our experience has be very positive, qnote that XEmacs is not
an embeddable library, nor is there provision in the mainline versions for
embedding other interpreters in XEmacs. So we've never had to worry about the
issues that come with that.
For more technical details, you could ask Ben Wing <[email protected]> who put a
lot of effort into the signal handling implementation, or Hrvoje Niksic (sorry,
no address offhand) who posts on python-dev occasionally. (I don't know if
Hrvoje ever worked on the signal handlers, and he hasn't worked on XEmacs for
years, but he was more familiar with internals than me then, and might very
well still remember more than I ever knew. :-) I don't think either will
disagree with my general statements above, though.
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