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From: Junio C Hamano <gitster@pobox.com>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH] t9300-fast-import: don't hang if background fast-import exits too early
Date: Sun, 01 Dec 2019 07:38:52 -0800	[thread overview]
Message-ID: <xmqq36e412er.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20191201093148.GH23183@szeder.dev> ("SZEDER =?utf-8?Q?G?= =?utf-8?Q?=C3=A1bor=22's?= message of "Sun, 1 Dec 2019 10:31:48 +0100")

SZEDER Gábor <szeder.dev@gmail.com> writes:

>> > -	test_when_finished "
>> > +	test_when_finished '
>> >  		exec 8>&-; exec 9>&-;
>> > -		kill $(cat V.pid) && wait $(cat V.pid)
>> > -		true"
>> > +		kill $(cat V.sh.pid) && wait $(cat V.sh.pid)
>> > +		kill $(cat V.fi.pid) && wait $(cat V.sh.pid)
>> > +		true'
>> 
>> The original interpolates the PID of the fast-import when
>> "when-finished" program is registered, so it is OK if somebody else
>> removed V.pid file; the new one interpolates when "when-finished"
>> program is run, reading from V.??.pid, so somebody needs to make
>> sure these pid files will stay around.  I do not think it is an
>> issue as I suspect we've left it to the global clean-up procedure
>> that removes the trash directory to remove the pid file.
>
> In the original the same shell process starts 'git fast-import',
> writes its pidfile, and registers the test_when_finished commands, so
> we can be sure that the pid file is already present when the shell
> runs the $(cat V.pid) command substitutions.

Yes.  It also means that V.pid file was not very useful in the
when-finished handler in the original.  We could have just used a
shell variable.

> With this patch that's not the case anymore, because the background
> subshell starts 'git fast-import' and writes the pidfile, but the main
> shell process registers the test_when_finished commands.  IOW these
> two shell processes are racing, and it's possible that the
> test_when_finished command is executed before the background subshell
> can write the pidfile.  So double quotes around the block of
> test_when_finished commands are not good.

Oh, I was not questioning that.  I wanted to make sure, and I was
doing so aloud, that these files are

 (1) created way before, and 
 (2) left on the filesystem

when-finished handler actually runs, because the original did not
need any guarantee for (2), but now the sq version does.

  reply	other threads:[~2019-12-01 15:39 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-30 10:46 [PATCH] t9300-fast-import: don't hang if background fast-import exits too early SZEDER Gábor
2019-11-30 21:16 ` Junio C Hamano
2019-12-01  9:31   ` SZEDER Gábor
2019-12-01 15:38     ` Junio C Hamano [this message]
2019-12-06 19:03 ` [PATCH v2 0/2] " SZEDER Gábor
2019-12-06 19:03   ` [PATCH v2 1/2] t9300-fast-import: store the PID in a variable instead of pidfile SZEDER Gábor
2019-12-06 19:03   ` [PATCH v2 2/2] t9300-fast-import: don't hang if background fast-import exits too early SZEDER Gábor

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