On 2013-10-16 14:30:34 -0400, Robert Haas wrote: > > But _and, _or are really useful because they can be used to atomically > > clear and set flag bits. > > Until we have some concrete application that requires this > functionality for adequate performance, I'd be inclined not to bother. > I think we have bigger fish to fry, and (to extend my nautical > metaphor) trying to get this working everywhere might amount to trying > to boil the ocean.
Well, I actually have a very, very preliminary patch using them in the course of removing the spinlocks in PinBuffer() (via LockBufHdr()). I think it's also going to be easier to add all required atomics at once than having to go over several platforms in independent feature patches adding atomics one by one. > > I was thinking of something like: > > include/storage/atomic.h > > include/storage/atomic-gcc.h > > include/storage/atomic-msvc.h > > include/storage/atomic-acc-ia64.h > > where atomic.h first has a list of #ifdefs including the specialized > > files and then lots of #ifndef providing generic variants if not > > already provided by the platorm specific file. > Seems like we might want to put some of this in one of the various > directories called "port", or maybe a new subdirectory of one of them. Hm. I'd have to be src/include/port, right? Not sure if putting some files there will be cleaner, but I don't mind it either. > This basically sounds sane, but I'm unwilling to commit to dropping > support for all obscure platforms we currently support unless there > are about 500 people +1ing the idea, so I think we need to think about > what happens when we don't have platform support for these primitives. I think the introduction of the atomics really isn't much dependent on the removal. The only thing I'd touch around platforms in that patch is adding a generic fallback pg_atomic_test_and_set() to s_lock.h and remove the special case usages of __sync_lock_test_and_set() (Arm64, some 32 bit arms). It's the patches that would like to rely on atomics that will have the problem :( 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
