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References: <CA+1R0Vg7b7YyvgDf1=or8oxskEX4BJwMJQxxTKYaUHWPQeD9iQ@mail.gmail.com>
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Date: Sun, 28 Dec 2025 11:52:36 -0800
Message-ID: <CA+1R0Vju3VQYaz-s00vCroEV3pH7vBeUhoMGqtUxi0x5k56vpQ@mail.gmail.com>
Subject: Re: flock deadlock
To: Takashi Yano <takashi.yano@nifty.ne.jp>, cygwin@cygwin.com
Content-Type: multipart/mixed; boundary="0000000000008d25320647087858"
From: Nahor via Cygwin <cygwin@cygwin.com>
Reply-To: Nahor <nahor.j+cygwin@gmail.com>
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie.com@cygwin.com>

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Attached is a reproducible example.
The example just calls `fork()` then open/flock/close a directory and
repeats (fork/open/flock/close). The forks optionally sleep then
open/flock/close the same directory and exit.

There is no issue if either the parent or the children don't call `flock()`.
Without sleeping, the example deadlocks immediately on my system 100%
of the time. Killing the child allow the parent to proceed, fork the
next child, which triggers the next deadlock.
When sleeping, _sometimes_ one child will deadlock with the parent.
Killing that child allows the parent and remaining children to proceed
(and potentially trigger another deadlock). Killing the parent also
unblocks all the children.

Regards,
Nahor.

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