Re: libpqrcv_PQexec() seems to violate latch protocol

On 06/06/17 23:17, Andres Freund wrote:
> On 2017-06-06 17:14:59 -0400, Tom Lane wrote:
>> Andres Freund <andres(at)anarazel(dot)de> writes:
>>> The function in $subject does:
>>
>>> ResetLatch(&MyProc->procLatch);
>>> rc = WaitLatchOrSocket(&MyProc->procLatch,
>>> WL_POSTMASTER_DEATH | WL_SOCKET_READABLE |
>>> WL_LATCH_SET,
>>> PQsocket(streamConn),
>>> 0,
>>> WAIT_EVENT_LIBPQWALRECEIVER);
>>
>> Yeah, this is certainly broken.
>>
>>> Afaict, the ResetLatch() really should just instead be in the if (rc & WL_LATCH_SET) block.
>>
>> And, to be specific, it should be before the CHECK_FOR_INTERRUPTS call,
>> since that is the useful work that we want to be sure occurs after
>> any latch-setting event.
>
> Right. I found a couple more instance of similarly iffy, although not
> quite as broken, patterns in launcher.c. It's easy to get this wrong,
> but it's a lot easy if you do it differently everywhere you use a
> latch. It's not good if code in the same file, by the same author(s),
> has different ways of using latches.

Huh? I see same pattern everywhere in launcher.c, what am I missing?

--
Petr Jelinek http://www.2ndQuadrant.com/
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