Re: NOTIFY does not work as expected

On 2018-10-18 18:39:34 -0400, Tom Lane wrote:
> Nope :-(. However, I got around to looking at this problem, and I concur
> with Jeff's diagnosis: the code around ProcessClientReadInterrupt is
> buggy because it does not account for the possibility that the process
> latch was cleared some time ago while unhandled interrupt-pending flags
> remain set. There are some other issues too:
>
> 1. ProcessClientWriteInterrupt has the same problem.
>
> 2. I don't believe the "blocked" vs "not-blocked" distinction one bit.
> At best, it creates race-condition-like changes in behavior depending
> on exactly when a signal arrives vs when data arrives or is sent.
> At worst, I think it creates the same problem it's purporting to solve,
> ie failure to respond to ProcDiePending at all. I think the
> before/during/after calls to ProcessClientXXXInterrupt should just all
> behave the same and always be willing to execute ProcDiePending.

That distinction was introduced because people (IIRC you actually) were
worried that we'd be less likely to get error messages out to the
client. Especially when you check unconditionally before actually doing
the write, it's going to be far less likely that we are able to send
something out to the client.

Greetings,

Andres Freund