Re: [HACKERS] Optional message to user when terminating/cancelling backend

On Fri, Aug 24, 2018 at 6:53 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> writes:
>> On Wed, Jul 25, 2018 at 7:27 PM, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:
>>> Seems the build of the updated patch built and tested Ok. Still have no idea
>>> why the previous one didn’t.
>
>> That problem apparently didn't go away. cfbot tested it 7 times in
>> the past week, and it passed only once on Windows:
>> https://ci.appveyor.com/project/postgresql-cfbot/postgresql/build/1.0.9691
>> The other times all failed like this:
>> https://ci.appveyor.com/project/postgresql-cfbot/postgresql/build/1.0.9833
>
> I think this is just a timing problem: the signal gets sent,
> but it might or might not get received before the current statement ends.
> It's possible that a signal-sent-to-self can be expected to be received
> synchronously on all Unix platforms, but I wouldn't entirely bet on that
> (in particular, the POSIX text for kill(2) does NOT guarantee it); and
> our Windows signal implementation certainly doesn't guarantee anything
> of the sort.

How about we just wait forever if the function manages to return?

select case when pg_cancel_backend(pg_backend_pid(), '...') then
pg_sleep('infinity') end;

--
Thomas Munro
http://www.enterprisedb.com