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达并行计算一直是并行编程中的一个棘手问题。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的编程自然地捕获局部性，但不适合在大型共享数据结构上进行计算。目前的项目通过Chorus部分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、不断变化的共享内存数据结构上进行并行计算。Chorus的关键抽象是对象组装：堆中配备了控制线程的局部隔离区域。程序集可以强制修改自己，与其他程序集合并，并分裂成更小的程序集？通过这些对程序集的操作，Chorus捕获了并行性的不可预测的动态变化。这使得Chorus成为许多不规则数据并行应用程序（例如，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性，但在最坏的情况下没有并行性，并且其并行化仍然是一个开放和困难的挑战。该项目的预期结果包括对Chorus语义基础的新见解，以及将Chorus与现有的异步任务创建、定向同步和局部性抽象集成在一起的新语言结构。在系统构建端，该项目将把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。该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载组成的基准进行全面评估。

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.