Parallel programming with object assemblies

We present Chorus, a high-level parallel programming model suitable for irregular, heap-manipulating applications like mesh refinement and epidemic simulations, and JChorus, an implementation of the model on top of Java. One goal of Chorus is to express the dynamic and instance-dependent patterns of memory access that are common in typical irregular applications. Its other focus is locality of effects: the property that in many of the same applications, typical imperative commands only affect small, local regions in the shared heap. Chorus addresses dynamism and locality through the unifying abstraction of an object assembly: a local region in a shared data structure equipped with a short-lived, speculative thread of control. The thread of control in an assembly can only access objects within the assembly. While objects can migrate from assembly to assembly, such migration is local--i.e., objects only move from one assembly to a neighboring one--and does not lead to aliasing. Programming primitives include a merge operation, by which an assembly merges with an adjacent assembly, and a split operation, which splits an assembly into smaller ones. Our abstractions are race and deadlock-free, and inherently data-centric. We demonstrate that Chorus and JChorus allow natural programming of several important applications exhibiting irregular data-parallelism. We also present an implementation of JChorus based on a many-to-one mapping of assemblies to lower-level threads, and report on preliminary performance numbers.