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From: Johannes Sixt <j6t@kdbg.org>
To: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Jeff King <peff@peff.net>
Subject: Re: [PATCH 0/4] t5552: fix flakiness by introducing proper locking for GIT_TRACE
Date: Fri, 10 Aug 2018 18:15:36 +0200	[thread overview]
Message-ID: <811ded48-6f33-c46e-7bae-b9f7c7e8764c@kdbg.org> (raw)
In-Reply-To: <pull.17.git.gitgitgadget@gmail.com>

Am 09.08.2018 um 19:35 schrieb Johannes Schindelin via GitGitGadget:
> I reported a couple of times that t5552 is not passing reliably. It has now
> reached next, and will no doubt infect master soon.
> 
> Turns out that it is not a Windows-specific issue, even if it occurs a lot
> more often on Windows than elsewhere.
> 
> The culprit is that two processes try simultaneously to write to the same
> file specified via GIT_TRACE_PACKET, and it is not well defined how that
> should work, even on Linux.

Thanks for digging down to the root cause. As has been said, the 
behavior of O_APPEND is well-defined under POSIX, but last time I looked 
for equivalent feature on Windows, I did not find any.

Last time was when I worked around the same failure in 
t5503-tagfollow.sh in my private builds:

https://github.com/j6t/git/commit/9a447a6844b50b43746d9765b3ac809e2793d742

It is basically the same as Peff suggests: log only one side of the fetch.

As this buglet looks like a recurring theme, and a proper fix is 
preferable over repeated work-arounds. To me it looks like we need some 
sort of locking on Windows. Unless your friends at Microsoft have an ace 
in their sleeves that lets us have atomic O_APPEND the POSIX way...

-- Hannes

  parent reply	other threads:[~2018-08-10 16:15 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-09 17:35 [PATCH 0/4] t5552: fix flakiness by introducing proper locking for GIT_TRACE Johannes Schindelin via GitGitGadget
2018-08-09 17:35 ` [PATCH 1/4] Introduce a function to lock/unlock file descriptors when appending Johannes Schindelin via GitGitGadget
2018-08-09 19:01   ` Junio C Hamano
2018-08-10 18:32     ` Johannes Schindelin
2018-08-09 17:35 ` [PATCH 2/4] mingw: implement lock_or_unlock_fd_for_appending() Johannes Schindelin via GitGitGadget
2018-08-09 17:35 ` [PATCH 3/4] trace: lock the trace file to avoid racy trace_write() calls Johannes Schindelin via GitGitGadget
2018-08-09 17:35 ` [PATCH 4/4] trace: verify that locking works Johannes Schindelin via GitGitGadget
2018-08-09 19:47 ` [PATCH 0/4] t5552: fix flakiness by introducing proper locking for GIT_TRACE Jeff King
2018-08-09 20:49   ` Junio C Hamano
2018-08-09 21:08     ` Junio C Hamano
2018-08-09 21:32       ` Jeff King
2018-08-10 14:09     ` Jeff King
2018-08-10 15:58       ` Junio C Hamano
2018-08-10 15:58       ` Junio C Hamano
2018-08-10 16:43       ` Johannes Schindelin
2018-08-10 17:15         ` Jeff King
2018-08-10 18:40           ` Junio C Hamano
2018-08-10 19:34           ` Johannes Schindelin
2018-08-10 16:15 ` Johannes Sixt [this message]
2018-08-10 16:51   ` Jeff Hostetler
2018-08-10 16:57     ` Jeff Hostetler
2018-08-10 17:08     ` Johannes Sixt
2018-08-10 18:34   ` Junio C Hamano
2018-08-10 18:56     ` Jeff King
2018-08-13 19:02     ` [PATCH] mingw: enable atomic O_APPEND Johannes Sixt
2018-08-13 20:20       ` Junio C Hamano
2018-08-13 21:05         ` Johannes Sixt
2018-08-13 21:22           ` Ævar Arnfjörð Bjarmason
2018-08-13 21:55             ` Junio C Hamano
2018-08-13 22:37             ` Jeff King
2018-08-14 13:47               ` Ævar Arnfjörð Bjarmason
2018-08-14 14:53                 ` Jeff King
2018-08-14 18:29               ` Johannes Sixt
2018-08-14 19:17                 ` Jeff King
2018-08-14 13:01       ` Jeff Hostetler
2018-08-14 14:38         ` Junio C Hamano
2018-08-10 19:47 ` [PATCH v2 0/4] t5552: fix flakiness by introducing proper locking for GIT_TRACE Johannes Schindelin via GitGitGadget
2018-08-10 19:47   ` [PATCH v2 1/4] Introduce a function to lock/unlock file descriptors when appending Johannes Schindelin via GitGitGadget
2018-08-10 20:05     ` Junio C Hamano
2018-08-10 21:31       ` Johannes Schindelin
2018-08-10 19:47   ` [PATCH v2 2/4] mingw: implement lock_or_unlock_fd_for_appending() Johannes Schindelin via GitGitGadget
2018-08-10 19:47   ` [PATCH v2 3/4] trace: lock the trace file to avoid racy trace_write() calls Johannes Schindelin via GitGitGadget
2018-08-10 19:47   ` [PATCH v2 4/4] trace: verify that locking works Johannes Schindelin via GitGitGadget

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