Re: Race conditions with checkpointer and shutdown

On Wed, Apr 17, 2019 at 10:45 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I think what we need to look for is reasons why (1) the postmaster
> never sends SIGUSR2 to the checkpointer, or (2) the checkpointer's
> main loop doesn't get to noticing shutdown_requested.
>
> A rather scary point for (2) is that said main loop seems to be
> assuming that MyLatch a/k/a MyProc->procLatch is not used for any
> other purposes in the checkpointer process.  If there were something,
> like say a condition variable wait, that would reset MyLatch at any
> time during a checkpoint, then we could very easily go to sleep at the
> bottom of the loop and not notice that there's a pending shutdown request.

Agreed on the non-composability of that coding, but if there actually
is anything in that loop that can reach ResetLatch(), it's well
hidden...

-- 
Thomas Munro
https://enterprisedb.com