Exploiting Implicit Parallelism in Dynamic Array Programming

We have built an interpreter for the array programming language J. The interpreter exploits implicit data parallelism in the language to achieve good parallel speedups on a variety of benchmark applications. Many array programming languages operate on entire arrays without the need to write loops. Writing without loops simplifies the programs. Array programs without loops allow an interpreter to parallelize the execution of the code without complex analysis or input from the programmer. The J programming language includes the usual idioms of operations on arrays of the same size and shape, where the operations can often be performed in parallel for each individual item of the operands. Another opportunity comes from Js reduction operations, where suitable operations can be performed in parallel for all the items of an operand. J has a notion of verb rank, which allows programmers to simplify programs by declaring how operations are applied to operands. The verb rank mechanism allows us to extract further parallelism. Our implementation of an implicitly parallelizing interpreter for J is written entirely in Java. We have written the interpreter in a framework that produces native code for the interpreter, giving good scalar performance. The interpreter itself is responsible for exploiting the parallelism available in the applications. Our results show we attain good parallel speed-up on a variety of benchmarks, including near perfect linear speed-up on inherently parallel benchmarks. We believe that the lessons learned from our approach to exploiting data parallelism in an interpreter can be applied to other interpreted languages as well.