On 2014-06-27 13:04:02 -0400, Robert Haas wrote: > On Thu, Jun 26, 2014 at 6:40 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Andres Freund <and...@2ndquadrant.com> writes: > >> On 2014-06-26 14:13:07 -0700, Tom Lane wrote: > >>> Surely it had better be a read barrier as well? > > > >> I don't immediately see why it has to be read barrier? Hoisting a load > >> from after the release into the locked area of code should be safe? > > > > No doubt, but delaying a read till after the unlocking write would > > certainly not be safe. > > > > AFAICT, README.barrier completely fails to define what we think the > > semantics of pg_read_barrier and pg_write_barrier actually are, so if > > you believe that a write barrier prevents reordering of reads relative to > > writes, you'd better propose some new text for that file. It certainly > > doesn't say that today. > > The relevant text is in barrier.h
Note that that definition of a write barrier is *not* sufficient for the release of a lock... As I said elsewhere I think all the barrier definitions, except maybe alpha, luckily seem to be strong enough for that anyway. Do we want to introduce acquire/release barriers? Or do we want to redefine the current barriers to be strong enough for that? Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
