VarHandle.compareAndSet is strong in two ways - non-spurious and sequentially consistent.
VarHandle.weakCompareAndSet is weak in both these ways. (That seems like a mistake to me. The fact that j.u.c. Atomic classes are a precedent for this seems unfortunate.) http://download.java.net/java/jdk9/docs/api/java/lang/invoke/VarHandle.html#weakCompareAndSet-java.lang.Object...- Sequential consistency should always be the default behavior of an unqualified cas operation - users should have to go out of their way to request relaxed reads or writes. C++ reasonably makes you use e.g. std::atomic_compare_exchange_weak_explicit. I was surprised that weakCompareAndSetAcquire used relaxed writes! I would expect that almost everyone would be happy with sequentially consistent, and almost everyone else would be happy with acquire-release, a variant we don't offer! And a few others would be happy with fully relaxed but single-variable sequentially consistent (but Java, unlike C++, doesn't promise that!).
