On Wed, Oct 16, 2013 at 12:52 PM, Andres Freund <and...@2ndquadrant.com> wrote: >> I have a related problem, which is that some code I'm currently >> working on vis-a-vis parallelism can run lock-free on platforms with >> atomic 8 bit assignment but needs a spinlock or two elsewhere. So I'd >> want to use pg_atomic_store_u64(), but I'd also need a clean way to >> test, at compile time, whether it's available. > > Yes, definitely. There should be a couple of #defines that declare > whether non-prerequisite options are supported. I'd guess we want at least: > * 8byte math > * 16byte compare_and_swap
I'm not terribly excited about relying on 16-byte CAS, but I agree that 8-byte math, at least, is important. I've not been successful in finding any evidence that gcc has preprocessor symbols to tell us about the properties of 8-byte loads and stores. The closest thing that I found is: http://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html That page provides intrinsics for 8-byte atomic loads and stores, among other things. But it seems that the only method for determining whether they work on a particular target is to compile a test program and see whether it complains about __atomic_load_n and/or __atomic_store_n being unresolved symbols. I suppose we could add a configure test for that. Yuck. Anyone have a better idea? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
