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Date:	Thu, 5 Feb 1998 00:01:30 -0500
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From:	smarry@pantransit.smar.reptiles.org
To:	broman@nosc.mil, culliton@clark.net
Subject: Re: "rc" shell maintainer?
Cc:	debian-devel@lists.debian.org, rc@hawkwind.utcs.toronto.edu

Hello, this is Marc Moorcroft.  I joined the list shortly after
running into two problems with rc-1.5b2 under Linux.

One definite bug (reported to Tim Goodwin) will cause rc to spin calling
wait(2) if you do:

{ls & wait} | cat

There is another problem with signal handling that is a little more
complicated.  When I upgraded to the 2.0.33 kernel, rc began hanging
occasionally when I interrupted programs, and when I finally got irritated
enough to check it thoroughly, I found that it failed trip.rc at:

kill -2 $pid

The relevant code is rc_wait() in wait.c:

static pid_t rc_wait(int *stat) {
	int r;
	interrupt_happened = FALSE;
	if (!setjmp(slowbuf.j)) {
		slow = TRUE;
		if (!interrupt_happened)
			r = wait(stat);
		else
			r = -1;
	} else
		r = -1;
	slow = FALSE;
	return r;
}

It appears that some of the time, Linux will return from the wait(2)
for the 'kill' process before the signal gets delivered.  On Linux
installations where signal(2) has the System V behaviour (system calls
are interrupted for signals that are caught via signal(2)) rc longjmps
out of the signal handler (a rather alarming practice in itself) to the
top of the enclosing code in rc_wait().  The sequence of events appears
to be:

	The signal is sent,

	the process exits,

	wait(2) returns successfully, and

	before the longjmp gadgetry can be turned off (slow = FALSE),
	the signal handler IMMEDIATELY runs,

	longjmps back to the top of the setjmp block,

and the PID that wait(2) returned is lost.  rc loops forever calling
wait(2) with no children, waiting for the lost PID to turn up.

I've talked to others who have had different problems on other Linux
installations, where caught signals do not interrupt system calls, as
in BSD.  This appears to be due to a difference of opinion between the
libc and glibc people about how signals should behave, but I haven't
investigated it myself.