Re: [HACKERS] 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@anarazel.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?

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