Re: Add non-blocking version of PQcancel

On Fri, Mar 25, 2022 at 2:47 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I think you misunderstand where the real pain point is. The reason
> that PQcancel's functionality is so limited has little to do with
> blocking vs non-blocking, and everything to do with the fact that
> it's designed to be safe to call from a SIGINT handler. That makes
> it quite impractical to invoke OpenSSL, and probably our GSS code
> as well. If we want support for all connection-time options then
> we have to make a new function that does not promise signal safety.

Well, that's a fair point, but it's somewhat orthogonal to the one I'm
making, which is that a non-blocking version of function X might be
expected to share code or at least functionality with X itself. Having
something that is named in a way that implies asynchrony without other
differences but which is actually different in other important ways is
no good.

> I'm prepared to yield on the question of whether we should provide
> a non-blocking version, though I still say that (a) an easier-to-call,
> one-step blocking alternative would be good too, and (b) it should
> not be designed around the assumption that there's a completely
> independent state object being used to perform the cancel. Even in
> the non-blocking case, callers should only deal with the original
> PGconn.

Well, this sounds like you're arguing for the first of the two
approaches I thought would be acceptable, rather than the second.

> > Leaving the question of approach aside, I think it's fairly clear that
> > this patch cannot be seriously considered for v15.
>
> Yeah, I don't think it's anywhere near fully baked yet. On the other
> hand, we do have a couple of weeks left.

We do?

--
Robert Haas
EDB: http://www.enterprisedb.com