Re: HandleParallelMessages contains CHECK_FOR_INTERRUPTS?

I wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
>> I notice you just removed the CHECK_FOR_INTERRUPTS in
>> HandleParallelMessages().  Did you notice that HandleParallelMessages
>> calls shm_mq_receive(), which calls shm_mq_receive_bytes(), which
>> contains a CHECK_FOR_INTERRUPTS() call?

After study, I believe that that CHECK_FOR_INTERRUPTS() is unreachable
given that HandleParallelMessages passes nowait = true.  But it's not
unlikely that future changes in shm_mq.c might introduce such calls that
are reachable.

> I wonder whether we should make use of HOLD_INTERRUPTS/RESUME_INTERRUPTS
> to avoid the recursion scenario here.

I concluded that that would be good future-proofing, whether or not it's
strictly necessary today, so I pushed it.
        regards, tom lane