Re: spinlocks on HP-UX

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I'm actually not convinced that we're entirely consistent here about
> what we require the semantics of acquiring and releasing a spinlock to
> be. For example, on x86 and x86_64, we acquire the lock using xchgb,
> which acts a full memory barrier. But when we release the lock, we
> just zero out the memory address, which is NOT a full memory barrier.
> Stores can't cross it, but non-dependent loads of different locations
> can back up over it. That's pretty close to a full barrier, but it
> isn't, quite.

Right. That's why I wrote the comment as I did; it says what the actual
requirement is. There probably are cases where our implementations are
more restrictive than necessary (I hope none where they are weaker).

regards, tom lane