From: Jeff King <peff@peff.net>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: "Junio C Hamano" <gitster@pobox.com>,
git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: Is t7006-pager.sh racy?
Date: Sun, 21 Nov 2021 13:40:02 -0500 [thread overview]
Message-ID: <YZqSgu4XjPWnURju@coredump.intra.peff.net> (raw)
In-Reply-To: <20211024170349.GA2101@szeder.dev>
On Sun, Oct 24, 2021 at 07:03:49PM +0200, SZEDER Gábor wrote:
> > What makes us expect that the "git log" invocation should trigger a
> > SIGPIPE in the first place?
>
> A misunderstanding, perhaps, because those 'git log' commands with
> their early-exiting pagers rarely trigger SIGPIPE.
I happened to be looking in this area today[1], and I think it turns out
not to be "rarely", but rather "never" for some of the tests.
The test in question sets the pager to "does-not-exist". But in that
case we will realize immediately via run-command.c that we could not run
the pager, and will not even redirect our stdout to it.
For example, doing this:
GIT_PAGER=does-not-exist git -c alias.foo='!yes' -p foo
will never get SIGPIPE; it will just write infinitely to the original
stdout, and return success.
Whereas this:
GIT_PAGER=false git -c alias.foo='!yes' -p foo
will reliably get SIGPIPE. But even if we used it (with a while loop to
instead of "yes" address the portability concern), the tests in t7006
would still be wrong, because they are sending test-terminal's output to
a closed pipe (so we'd still see SIGPIPE regardless of Git's behavior).
They should be sending test_terminal's output to a file or /dev/null.
It seems like this thread stalled. Ævar, were you planning to fix these
tests?
It's not too hard to swap out a "yes" as I showed above, but it further
confuses the trace2 output, because now we have the child yes (or its
shell equivalent) exiting as well.
The non-child "log --stdin" example I gave earlier in the thread avoids
that, but the fifo hackery is so horrible that I'd just as soon avoid
it. I guess yet another option is a builtin which produces infinite
output. Perhaps:
oid=$(git rev-parse HEAD)
while true; do echo $oid; done |
test_terminal git -p cat-file --batch-check
That's guaranteed to get SIGPIPE eventually if the pager stops reading.
I seem to recall that test_terminal's handling of stdin is somewhat
broken, though, and would probably get in our way[2]. Possibly we could
just rip it out, as nobody is relying on it (they can't be, because it's
broken).
-Peff
[1] https://lore.kernel.org/git/YZqSBlvzz2KgOMnJ@coredump.intra.peff.net/
[2] https://lore.kernel.org/git/20190520125016.GA13474@sigill.intra.peff.net/
next prev parent reply other threads:[~2021-11-21 18:40 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-24 0:04 Is t7006-pager.sh racy? Junio C Hamano
2021-10-24 17:03 ` SZEDER Gábor
2021-10-25 17:41 ` Jeff King
2021-10-28 19:55 ` SZEDER Gábor
2021-10-28 22:10 ` Jeff King
2021-11-21 18:40 ` Jeff King [this message]
2021-11-21 22:05 ` Jeff King
2021-11-21 22:54 ` [PATCH] t7006: clean up SIGPIPE handling in trace2 tests Jeff King
2021-11-21 23:10 ` Jeff King
2021-11-22 2:17 ` Junio C Hamano
2021-11-22 4:51 ` Jeff King
2021-11-22 4:54 ` Jeff King
2021-11-22 5:49 ` Junio C Hamano
2021-11-22 6:05 ` Junio C Hamano
2021-11-22 19:11 ` Jeff King
2021-11-22 21:28 ` [PATCH] run-command: unify signal and regular logic for wait_or_whine() Jeff King
2021-12-01 14:03 ` Is t7006-pager.sh racy? Ævar Arnfjörð Bjarmason
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