On Thu, 29 Jun 2017, Andrew Haley wrote: > I think I now properly understand Richard Earnshaw's point: that we > *do* support a full set of atomic primitives for 16-byte types via > libatomic, but for them to work as a sequentially-consistent set we > must use the same locking scheme for all of them. It's ugly, and > horrible for anyone who simply wants a double-word CAS, but it is what > it is. We can't use LDXP because it isn't atomic on its own, and the > ARM manual is quite explicit about this. Anyone who wants to use > a real compare-and-swap-16 is on their own. Note that there's no 'atomic read' primitive among __sync builtins, so IMO it gives a way out: expose native doubleword cas via __sync_compare_and_swap, use a locking scheme for its __atomic counterpart. Alexander
