Re: Parallel worker hangs while handling errors.

On Fri, Aug 7, 2020 at 1:34 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Tue, Jul 28, 2020 at 5:35 AM Bharath Rupireddy
> <bharath.rupireddyforpostgres@gmail.com> wrote:
> > The v4 patch looks good to me. Hang is not seen, make check and make
> > check-world passes. I moved this to the committer for further review
> > in https://commitfest.postgresql.org/29/2636/.
>
> I don't think I agree with this approach. In particular, I don't
> understand the rationale for unblocking only SIGUSR1. Above, Vignesh
> says that he feels that unblocking only that signal would be the right
> approach, but no reason is given. I have two reasons why I suspect
> it's not the right approach. One, it doesn't seem to be what we do
> elsewhere; the only existing cases where we have special handling for
> particular signals are SIGQUIT and SIGPIPE, and those places have
> comments explaining the reason why they are handled in a special way.
> Two, SIGUSR1 is used for a LOT of things: look at all the different
> cases procsignal_sigusr1_handler() checks. If the intention is to only
> allow the things we know are safe, rather than all the signals there
> are, I think this coding utterly fails to achieve that - and for
> reasons that I don't think are really fixable.
>

My intention of blocking only SIGUSR1 over unblocking all signals
mainly because we are already in the error path and we are about to
exit after emitting the error report. I was not sure if we intended to
receive any other signal just before exiting.
The Solution Robert & Tom are suggesting by Calling
BackgroundWorkerUnblockSignals fixes the actual problem.

Regards,
Vignesh
EnterpriseDB: http://www.enterprisedb.com