- memory_order_acquire: guarantees that subsequent loads are not moved before the current load or any preceding loads.
- memory_order_release: preceding stores are not moved past the current store or any subsequent stores.
- memory_order_acq_rel: combines the two previous guarantees.
- memory_order_consume: potentially weaker form of memory_order_acquire that enforces ordering of the current load before other operations that are data-dependent on it (for instance, when a load of a pointer
is marked memory_order_consume, subsequent operations that dereference this pointer won’t be moved before it (yes, even that is not guaranteed on all platforms!). - memory_order_relaxed: all reorderings are okay.
One can see more information about memory order from a paper called Shared Memory Consistency Models: A Tutorial