Strictly speaking, the Java Memory Model derives from the data-race-free model of the early '90s. Java was the first programming language to explicitly incorporate it as part of the specification, but the main derivation actually comes from the C++ memory model, which built into it the basic atomic memory model that most derivatives rely on--Java doesn't have the weaker atomics support that C++ added, just sequentially-consistent. Java also introduced some frankly confusing (and incorrect, per my understanding) semantics for what happens in the face of data races that everybody else just shrugged and said "let's make it be UB and call it a day."
Okay, it looks like those were added in Java 9, which was after I stopped following Java (and well after the C++ memory model was largely settled, in 2007).
Not with the Unsafe class. It was never intended to be used by anything except the built-in concurrency support classes, and it was just barely good enough. External libraries which made use of the Unsafe class did so by studying how it was used, and then assumed/concluded how it worked. Java 9 formalized everything with the VarHandle class, and it offers much more features than the Unsafe class.
Thanks for the clarification. Java was obviously a trailblazer on formally introducing advanced memory models on practical languages, but it did take a few tries to get it correct.
Why is Hanz Boehm referring to memory model fixes and the JMM in the C++11 spec (Java started tackling this problem in 2004, see Goetz) if Java copied C++?
