Generative Operational Semantics for Relaxed Memory Models ⋆

Abstract. The specification of the Java Memory Model (JMM) is phrased in terms of acceptors of execution sequences rather than the standard generative view of operational semantics. This creates a mismatch with language-based techniques, such as simulation arguments and proofs of type safety. We describe a semantics for the JMM using standard programming language techniques that captures its full expressivity. For data-race-free programs, our model coincides with the JMM. For lockless programs, our model is more expressive than the JMM. The stratification properties required to avoid causality cycles are derived, rather than mandated in the style of the JMM. The JMM is arguably non-canonical in its treatment of the interaction of data races and locks as it fails to validate roach-motel reorderings and various peephole optimizations. Our model differs from the JMM in these cases. We develop a theory of simulation and use it to validate the legality of the above optimizations in any program context.