On Wed, Nov 16, 2022 at 8:42 PM Andres Freund <andres@anarazel.de> wrote:
> Afaict the problem is that
> proc = (PGPROC *) &(waitQueue->links);
>
> is a gross gross hack - this isn't actually a PGPROC, it's pointing to an
> SHM_QUEUE, but *not* one embedded in PGPROC. It kinda works because ->links
> is at offset 0 in PGPROC, which means that
> SHMQueueInsertBefore(&(proc->links), &(MyProc->links));
> will turn &proc->links back into waitQueue->links. Which we then can enqueue
> again.
Not that I object to a targeted fix, but it's been 10 years since
slist and dlist were committed, and we really ought to eliminate
SHM_QUEUE entirely in favor of using those. It's basically an
open-coded implementation of something for which we now have a
toolkit. Not that it's impossible to make this kind of mistake with a
toolkit, but in general open-coding the same logic in multiple places
increases the risk of bugs.
--
Robert Haas
EDB: http://www.enterprisedb.com