On Thu, Jun 26, 2014 at 5:20 AM, Andres Freund <and...@2ndquadrant.com> wrote: > On 2014-06-25 20:16:08 -0400, Robert Haas wrote: >> On Wed, Jun 25, 2014 at 4:36 PM, Andres Freund <and...@2ndquadrant.com> >> wrote: >> > Since it better be legal to manipulate a atomic variable while holding a >> > spinlock we cannot simply use an arbitrary spinlock as backing for >> > atomics. That'd possibly cause us to wait on ourselves or cause >> > deadlocks. >> >> I think that's going to fall afoul of Tom's previously-articulated "no >> loops inside spinlocks" rule. Most atomics, by nature, are >> loop-until-it-works. > > Well, so is TAS itself :). > > More seriously, I think we're not going to have much fun if we're making > up the rule that you can't do an atomic add/sub while a spinlock is > held. That just precludes to many use cases and will make the code much > harder to understand. I don't think we're going to end up having many > problems if we allow atomic read/add/sub/write in there.
That rule seems reasonable -- why would you ever want to do this? While you couldn't properly deadlock it seems like it could lead to unpredictable and hard to diagnose performance stalls. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
