I wrote:
>> So that's trouble waiting to happen, for sure.  At the very least we
>> need to do a single fetch of WalRcv->latch, not two.  I wonder whether
>> even that is sufficient, though: this coding requires an atomic fetch of
>> a pointer, which is something we generally don't assume to be safe.

BTW, I had supposed that this bug was of long standing, but actually it's
new in v10, dating to 597a87ccc9a6fa8af7f3cf280b1e24e41807d555.  Before
that walreceiver start/stop just changed the owner of a long-lived shared
latch, and there was no question of stale pointers.

I considered reverting that decision, but the reason for it seems to have
been to let libpqwalreceiver.c manipulate MyProc->procLatch rather than
having to know about a custom latch.  That's probably a sufficient reason
to justify some squishiness in the wakeup logic.  Still, we might want to
revisit it if we find any other problems here.

                        regards, tom lane

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