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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Cleaning up historical portability baggage
Date: Sat, 06 Aug 2022 18:42:03 -0400
Message-ID: <146576.1659825723@sss.pgh.pa.us> (raw)
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Thomas Munro <thomas.munro@gmail.com> writes:
> Did I understand correctly that the places that do kill(-pid) followed
> by kill(pid) really only need the kill(-pid)?

Uh ... did you read the comment right above signal_child?

 * There is a race condition for recently-forked children: they might not
 * have executed setsid() yet.  So we signal the child directly as well as
 * the group.  We assume such a child will handle the signal before trying
 * to spawn any grandchild processes.  We also assume that signaling the
 * child twice will not cause any problems.

It might be that this is wrong and signaling -pid will work even if
the child hasn't yet done setsid(), but I doubt it: the kill(2) man
page is pretty clear that it'll fail if "the process group doesn't
exist".

Perhaps we could finesse that by signaling -pid first, and then
signaling pid if that fails, but offhand it seems like that has
the described race condition w.r.t. grandchild processes.

			regards, tom lane





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  Cc: tgl@sss.pgh.pa.us, thomas.munro@gmail.com, robertmhaas@gmail.com, andrew@dunslane.net, andres@anarazel.de
  Subject: Re: Cleaning up historical portability baggage
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