From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Andres Freund <andres@anarazel.de>,
        Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Issue with cancel_before_shmem_exit while searching to remove a
 particular registered exit callbacks
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Mon, 10 Aug 2020 15:33:15 -0400"
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Date: Mon, 10 Aug 2020 15:41:33 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> Perhaps we really have four categories here:
> (1) Temporary handlers for PG_ENSURE_ERROR_CLEANUP().
> (2) High-level cleanup that needs to run after aborting out of the
> current transaction.
> (3) Per-subsystem shutdown for shared memory stuff.
> (4) Per-subsystem shutdown for backend-private stuff.

Hmm, I don't think we actually have any of (2) do we?  Or at least
we aren't using ipc.c callbacks for them.

> What I do think we should do, after thinking about it more,
> is discourage the casual use of before_shmem_exit() for things where
> on_shmem_exit() or on_proc_exit() would be just as good. I think
> that's what would avoid the most problems here.

I think we're mostly in violent agreement here.  The interesting
question seems to be Andres' one about whether before_shmem_exit
actually has any safe use except for PG_ENSURE_ERROR_CLEANUP.
It may not, in which case perhaps we oughta rename it?

			regards, tom lane