InContext: simple parallelism for distributed applications

As networking services, such as DHTs, provide increasingly complex functionality, providing acceptable performance will require parallelizing their operations on individual nodes. Unfortunately, the event-driven style in which these applications have traditionally been written makes it difficult to reason about parallelism, and providing safe, efficient parallel implementations of distributed systems remains a challenge. In this paper, we introduce a declarative programming model based on contexts, which allows programmers to specify the sharing behavior of event handlers. Programs that adhere to the programming model can be safely parallelized according to an abstract execution model, with parallel behavior that is well-defined with respect to the expected sequential behavior. The declarative nature of the programming model allows conformance to be captured as a safety property that can be verified using a model checker. We develop a prototype implementation of our abstract execution model and show that distributed applications written in our programming model can be automatically and efficiently parallelized. To recover additional parallelism, we present an optimization to the implementation based on state snapshots that permits more events to proceed in parallel. We evaluate our prototype implementation through several case studies and demonstrate significant speedup over optimized sequential implementations.