Semantic Language Extensions for Implicit Parallel Programming

Several emerging fields of science and engineering are increasingly characterized by computationally intensive programs. Without parallelization, such programs do not benefit from the increasing core counts available in todays chip multiprocessors. However, writing correct and well-performing parallel programs is widely perceived to be an extremely hard problem. In order to understand the challenges faced by scientific programmers in effectively leveraging parallel computation, this dissertation first presents an in-depth field study of the practice of computational science. Based on the results of the field study, this dissertation proposes two new implicit parallel programming (IPP) solutions. With IPP, artificial constraints imposed by sequential models for automatic parallelization are overcome by use of semantic programming extensions. These preserve the ease of sequential programming and enable multiple parallelism forms without additional parallelism constructs, achieving the best of both automatic and explicit parallelization. The first IPP solution, Commutative Set, generalizes existing notions of semantic commutativity. It allows a programmer to relax execution orders prohibited under a sequential programming model with a high degree of expressiveness. The second IPP solution, WeakC, provides language extensions to relax strict consistency requirements of sequential data structures, and dynamically optimizes a parallel configuration of these data structures via a combined compiler-runtime system. This dissertation evaluates both Commutative Set and WeakC on real-world applications running on real hardware, including some that are actively used by some scientists in their day-to-day research. The detailed experimental evaluation results demonstrate the effectiveness of the proposed techniques.