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From: janssen@titan.sw.mcc.com (Bill Janssen)
Newsgroups: comp.emacs,gnu.emacs.bug
Subject: Re: 18.52 and X11
Message-ID: <1464@titan.>
Date: 28 Oct 88 00:28:53 GMT
References: <4933@garfield.MUN.EDU> <358@infovax.lan.informatik.tu-muenchen.dbp.de> <88Oct25.175431edt.40365@dopey.white.toronto.edu>
Sender: janssen@titan.
Reply-To: janssen@titan.sw.mcc.com (Bill Janssen)
Followup-To: comp.emacs
Organization: MCC Software Technology
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In-reply-to: cks@white.toronto.edu (Chris Siebenmann)

I had a problem that may or may not be similar with a branch variant
of GNU Emacs we run here, under X.  Every so often it would go into a
very compute-intensive loop, but not doing anything to the X-window
it was running in.  We tracked this down to a bug in the "fcntl" code
for sockets, in that only the group leader of the process group
received SIGIO's, though the code *apparently* sets up the groups so
that all members of the group will receive SIGIO.  The emacs code under
X basically sits in a select statement, waiting for input to be delivered
from the X server or from some dependent process.  When input comes in
from the X server, it expects to see that a SIGIO has happened before
the select has returned.  When the select returns, Emacs checks a flag
to see if a SIGIO has been delivered.  If it has, it goes to read the
X socket.  If not, it goes back into its select.

Under some conditions, Emacs is not the group leader of its process group,
and never receives SIGIO.  If you are running with INTERRUPT_INPUT, it
will continue to bounce out of and back into that select statement forever.

A quick fix is to slap a "setpgrp" statement in somewhere, so that
Emacs is always the process leader of its process group.  Another fix,
and I thought this was already in the 18.51 code, was to check the
input a bit differently when coming out of the select statement.

Bill