Systematic Testing of Multithreaded Programs

We present a practical testing algorithm called ExitBlock that systematically and deterministically nds program errors resulting from unintended timing dependencies. ExitBlock executes a program or a portion of a program on a given input multiple times, enumerating meaningful schedules in order to cover all program behaviors. Previous work on systematic testing focuses on programs whose concurrent elements are processes that run in separate memory spaces and explicitly declare what memory they will be sharing. ExitBlock extends previous approaches to multithreaded programs in which all of memory is potentially shared. A key challenge is to minimize the number of schedules executed while still guaranteeing to cover all behaviors. Our approach relies on the fact that for a program following a mutual-exclusion locking discipline, enumerating possible orders of the synchronized regions of the program covers all possible behaviors of the program. We describe in detail the basic algorithm and extensions to take advantage of readwrite dependency information and to detect deadlocks.