Isolating Determinism in Multi-threaded Programs

Futures are a program abstraction that express a simple form of fork-join parallelism. The expression future (e) declares that e can be evaluated concurrently with the future’s continuation. Safe-futures provide additional deterministic guarantees, ensuring that all data dependencies found in the original (non-future annotated) version are respected. In this paper, we present a dynamic analysis for enforcing determinism of safe-futures in an ML-like language with dynamic thread creation and first-class references. Our analysis tracks the interaction between futures (and their continuations) with other explicitly defined threads of control, and enforces an isolation property that prevents the effects of a continuation from being witnessed by its future, indirectly through their interactions with other threads. Our analysis is defined via a lightweight capability-based dependence tracking mechanism that serves as a compact representation of an effect history. Implementation results support our premise that futures and threads can extract additional parallelism compared to traditional approaches for safe-futures.