Verifying Synchronization for Atomicity Violation Fixing

Atomicity is a fundamental property to guarantee the isolation of a work unit (i.e., a sequence of related events in a thread) from concurrent threads. However, ensuring atomicity is often very challenging due to complex thread interactions. We present an approach to help developers verify whether such work units, which have triggered bugs due to certain violations of atomicity, are sufficiently synchronized or not by locks introduced for fixing the bugs. A key feature of our approach is that it combines the fortes of both bug-driven and change-aware techniques, which enables it to effectively verify synchronizations by testing only a minimal set of suspicious atomicity violations without any knowledge on the to-be-isolated work units, thus being more efficient and practical than other approaches. Besides, unlike existing approaches, our approach effectively utilizes all the inferred execution traces even they may not be completely feasible, such that the verification algorithm can converge much faster. We demonstrate via extensive evaluation that our approach is much more effective and efficient than the state-of-the-arts. Besides, we show that although there have existed sound automatic fixing techniques for atomicity violations, our approach is still necessary and useful for quality assurance of concurrent programs, because the assumption behind our approach is much weaker. We have also investigated one of the largest bug databases and found that insufficient synchronizations are common and difficult to be found in software development.