Drinking from both glasses: combining pessimistic and optimistic tracking of cross-thread dependences

Abstract

It is notoriously challenging to develop parallel software systems that are both scalable and correct. Runtime support for parallelism---such as multithreaded record & replay, data race detectors, transactional memory, and enforcement of stronger memory models---helps achieve these goals, but existing commodity solutions slow programs substantially in order to track (i.e., detect or control) an execution's cross-thread dependences accurately. Prior work tracks cross-thread dependences either "pessimistically," slowing every program access, or "optimistically," allowing for lightweight instrumentation of most accesses but dramatically slowing accesses involved in cross-thread dependences.