SHF: Medium: Collaborative Research: Chorus: Dynamic Isolation in Shared-Memory Parallelism

在复杂的共享内存数据结构上表示并行计算一直是并行编程中一个令人头疼的问题。一方面，流行的基于任务的编程模型没有为隔离和局部性提供一流的抽象。另一方面，基于Actor的编程自然会捕获局部性，但不适合在大型共享数据结构上进行计算。本项目通过Chorus部分地弥合了这两种并行风格之间的差距，Chorus是一种新的编程模型，用于在非结构化的、不断变化的共享内存数据结构上进行并行计算。Chorus的关键抽象是对象程序集：堆中配备了控制线程的本地隔离区域。程序集可以修改自身，与其他程序集合并，并拆分成更小的程序集？通过对程序集的这些操作，Chorus捕获了不可预测的、动态的并行度变化。这使得Chorus成为许多不规则数据并行应用程序(如网格、集群)的理想编程模型，这些应用程序在典型执行中表现出细粒度的数据并行，但在最坏的情况下没有并行，其并行化仍然是一个开放和困难的挑战。该项目的预测结果包括对Chorus的语义基础的新见解，以及将Chorus与现有抽象集成在一起的新语言构造，用于异步任务创建、定向同步和局部性。在系统构建方面，该项目将Chorus与Habanero Java并行编程语言集成在一起，并为生成的语言实现编译器和运行时。这种语言的性能和可编程性将使用主要由新出现的不规则工作负荷组成的基准进行彻底评估。

Expressing parallel computations over complex shared-memory data structures has always been a vexing issue in parallel programming. On one hand, popular task-based programming models do not provide first-class abstractions for isolation and locality. On the other, Actor-based programming naturally captures locality but is unsuitable for computations on large shared data structures. The present project partially bridges the gap between these two styles of parallelism through Chorus, a new programming model for parallel computations over unstructured, continually changing shared-memory data structures. The key abstraction of Chorus is an object assembly: a local, isolated region in the heap equipped with a thread of control. Assemblies can imperatively modify themselves, merge with other assemblies, and split into smaller assemblies?through these operations over assemblies, Chorus captures unpredictable, dynamic changes to parallelism. This makes Chorus an ideal programming model for many irregular data-parallel applications (e.g., meshing, clustering), which exhibit fine-grained data-parallelism in typical executions but no parallelism in the worst case, and whose parallelization remains an open and difficult challenge.The predicted outcomes of the project include new insights into the semantic foundations of Chorus and new language constructs integrating Chorus with existing abstractions for asynchronous task creation, directed synchronization, and locality. On the system-building end, the project will integrate Chorus with the Habanero Java parallel programming language, and implement a compiler and runtime for the resultant language. The performance and programmability of this language will be thoroughly evaluated using benchmarks largely consisting of emerging irregular workloads.