Re: git does not wait on hook exes (^C)

From: Anthony Sottile <asottile@umich.edu>
To: Jeff King <peff@peff.net>
Cc: "brian m. carlson" <sandals@crustytoothpaste.net>,
	Git Mailing List <git@vger.kernel.org>
Subject: Re: git does not wait on hook exes (^C)
Date: Thu, 20 Feb 2020 22:08:08 -0800	[thread overview]
Message-ID: <CA+dzEBkGWdBm_=fbw97UmWg8DXtVrfGUFLDDrtmX-+bmkQaFjA@mail.gmail.com> (raw)
In-Reply-To: <20200221053221.GC1280313@coredump.intra.peff.net>

On Thu, Feb 20, 2020 at 9:32 PM Jeff King <peff@peff.net> wrote:
>
> On Fri, Feb 21, 2020 at 02:25:58AM +0000, brian m. carlson wrote:
>
> > On 2020-02-21 at 01:20:51, Anthony Sottile wrote:
> > > My hook in question is a python process: https://pre-commit.com
> > >
> > > It doesn't really do all that much on SIGINT but prints "(^C)
> > > Interrupted" and offers a crash log when receiving ^C -- this races
> > > with the git process terminating and causes terminal spew (sometimes
> > > with pretty bad consequences with input breaking until `reset`
> > > depending on which thing wins the tty reset race).
> >
> > Thanks, this is helpful context.  I don't know that Git waiting for the
> > process is going to fix the broken terminal state, although it will
> > likely fix the jumbled output.
> >
> > I'm not planning on writing a patch, but I think an interesting patch to
> > see might be if we called wait(2) in a loop in a SIGINT handler but
> > didn't reinstall the signal handler, which means that a second Ctrl-C
> > would kill Git.  I believe that's what certain other programs do, and
> > that might address many of the problems in both scenarios.
>
> The run-command struct has a clean_on_exit flag, as well as a
> wait_after_clean flag, that would do what you want: when we're killed by
> SIGINT, we'd pass the signal on to the child and then wait for to
> finish.  That first step should generally be unnecessary for SIGINT
> (since as you noted, it will usually be delivered to the whole process
> group), but it shouldn't hurt.
>
> To get the double-^C behavior, I think cleanup_children_on_signal()
> would have to be reordered to pop the signal handler first before
> calling cleanup_children().
>
> I'm not quite convinced that's all worth doing, or wouldn't have other
> unforeseen consequences. But if anybody is interested in experimenting,
> I think the patch would only be a few lines (set those flags when
> running hooks, and then that reordering).
>
> -Peff

The small patch at least solves my issues and prevents the zombie
processes so I've sent it to the mailing list -- thanks for the
pointer.  I had found `wait_after_clean` in my initial investigation
but had missed the `clean_on_exit` flag!

Anthony