An Effect System and Language for Deterministic - by - Default Parallel Programming

This thesis presents a new, Java-based object-oriented parallel language called Deterministic Parallel Java (DPJ). DPJ uses a novel effect system to guarantee determinism by default. That means that parallel programs are guaranteed to execute deterministically unless nondeterminism is explicitly requested. This is in contrast to the shared-memory models in widespread use today, such as threads and locks (including threads in ordinary Java). Those models are inherently nondeterministic, do not provide any way to check or enforce that a computation is deterministic, and can even have unintended data races, which can lead to strange and unexpected behaviors. Because deterministic programs are much easier to reason about than arbitrary parallel code, determinism by default simplifies parallel programming. This thesis makes several broad contributions to the state of the art in programming languages and effect systems. First, it presents a comprehensive research agenda for achieving determinism by default in parallel languages with reference aliasing and shared mutable state. It argues that an object-oriented effect system is a good approach to managing shared memory conflicts. It also raises several technical challenges, many of which are taken up in the rest of the thesis. Second, this thesis presents an effect system and language for deterministic parallel programming using a fork-join model of parallel control. With simple modular checking, and with no runtime checking overhead, the effect system guarantees at compile time that there are no conflicting memory accesses between any pairs of parallel tasks. The effect system supports several important patterns of deterministic parallelism that previous systems cannot express. We describe the effect system and language both formally and informally, and prove soundness for the formal language. We also describe our evaluation showing that the language can express a range of parallel programming patterns with good performance. Third, this thesis extends the effect system and language for determinism to support a controlled form of nondeterminism. Conflicting accesses are allowed only for an explicitly identified nondeterministic parallel construct, so the language is deterministic by default. A transactional runtime provides isolation for atomic