bug#10664: 24.0.93; JIT font-lock infloops in a C file

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> > I don't have a recipe starting from "emacs -Q", sorry.

>> > I left my freshly built Emacs 24.0.93 running, and when I returned to
>> > it a few hours later, I found it unresponsive, endlessly showing in
>> > the echo area "JIT lock socket.c", interspersed with GC messages
>> > (I have garbage-collection-messages set non-nil).

>> > Breaking into Emacs with a debugger produced the backtrace below (it's
>> > an optimized build, so the backtrace may be inaccurate, sorry).  I
>> > attach the file socket.c (part of the Guile sources) as well.

> I got something similar for this socket.c.  I load it into emacs -Q, then
> start scrolling downwards, a page at a time.  The first five scrolls are
> fine.  Then it hangs on the sixth.

While not easy, it should be theoretically possible to reproduce the
problem with (setq font-lock-support-mode nil) which would make it much
easier to debug.  If the problem doesn't appear right when enabling
font-lock, then it needs to be triggered by cutting and re-inserting
a chunk of text (and you need to find a chunk that triggers the problem).


        Stefan