Re: [PATCH 1/4] tests: factor portable signal check out of t0005

[Jeff King <peff@peff.net>]

On Fri, Jun 24, 2016 at 10:52:32PM +0200, Johannes Sixt wrote:

> Am 24.06.2016 um 21:43 schrieb Jeff King:
> > In POSIX shells, a program which exits due to a signal
> > generally has an exit code of 128 plus the signal number.
> > However, some platforms do other things. ksh uses 256 plus
> > the signal number, and on Windows, all signals are just "3".
> 
> That's not true, see below.

I was worried about that. Git for Windows seems like a labyrinth of
bizarre special cases.

> > I didn't get into the weirdness of SIGPIPE on Windows here, but I think
> > this is probably a first step toward handling it better. E.g., it may be
> > that test_match_signal should respect 128 (or even any code) when we are
> > checking for SIGPIPE.
> 
> The Windows behavior is most closely described as having signal(SIGPIPE,
> SIG_IGN) at the very beginning of the program.

Right, but then we would get EPIPE. So what does git do in such cases?
I'd expect it generally to either hit the check_pipe() part of
write_or_die(), or to end up complaining via die() that the write didn't
go as expected.

> > +# Returns true if the numeric exit code in "$2" represents the expected signal
> > +# in "$1". Signals should be given numerically.
> > +test_match_signal () {
> > +	if test "$2" = "$((128 + $1))"
> > +	then
> > +		# POSIX
> > +		return 0
> > +	elif test "$2" = "$((256 + $1))"
> > +	then
> > +		# ksh
> > +		return 0
> > +	elif test "$2" = "3"; then
> > +		# Windows
> 
> You meant well here, but this is close to pointless as a general check. We
> check for this exit code in t0005 because there program termination happens
> via raise(), which on Window just calls exit(3). This exit code is not an
> indication that something related to SIGPIPE (or any signal) happened.
> 
> IMO there is too much danger to trigger a false positive if exit code 3 is
> treated special in this generality.

Yeah, I agree. But what _should_ it do? E.g., what happens to git-daemon
when it is killed via TERM?

-Peff