Re: Win32 latch implementation revisited

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> It just occurred to me that the Windows latch implementation goes
> through a lot of trouble to dynamically assign the shared Windows event
> handles to the latches in OwnLatch, but there's really no reason why
> they can't be statically assigned in InitSharedLatch instead. We have to
> allocate the same amount of event handles anyway.

> That makes the implementation a lot simpler, eliminating the shared
> memory block dedicated to latches altogether, and all the related
> bookkeeping. We no longer need NumSharedLatches() function anymore
> either, each InitSharedLatch call can allocate a new event handle directly.

That sounds real good. The only possible downside I can see is this:

> + * InitSharedLatch needs to be called in postmaster before forking child
> + * processes, usually right after allocating the shared memory block
> + * containing the latch with ShmemInitStruct. The Unix implementation
> + * doesn't actually require that, but the Windows one does.

But realistically I think we have to insist on InitSharedLatch being
done during shared memory setup anyway, else there will be race
condition issues. So no objection here.

regards, tom lane