Re: [EXTERNAL] Re: Add non-blocking version of PQcancel

(resent because it was blocked from the mailing-list due to inclusion of a blocked email address in the To line)

From: Andres Freund <andres(at)anarazel(dot)de>
> On 2022-04-04 15:21:54 +0000, Jelte Fennema wrote:
> > 2. Added some extra sleeps to the cancellation test, to remove random
> > failures on FreeBSD.
>
> That's extremely extremely rarely the solution to address test reliability
> issues. It'll fail when running test under valgrind etc.
>
> Why do you need sleeps / can you find another way to make the test reliable?

The problem they are solving is racy behaviour between sending the query
and sending the cancellation. If the cancellation is handled before the query
is started, then the query doesn't get cancelled. To solve this problem I used
the sleeps to wait a bit before sending the cancelation request.

When I wrote this, I couldn't think of a better way to do it then with sleeps.
But I didn't like it either (and I still don't). These emails made me start to think
again, about other ways of solving the problem. I think I've found another
solution (see attached patch). The way I solve it now is by using another
connection to check the state of the first one.

Jelte