PFix: Fixing Concurrency Bugs Based on Memory Access Patterns

Abstract

Concurrency bugs of a multi-threaded program may only manifest with certain scheduling, i.e., they are heisenbugs which are observed only from time to time if we execute the same program with the same input multiple times. They are notoriously hard to fix. In this work, we propose an approach to automatically fix concurrency bugs. Compared to previous approaches, our key idea is to systematically fix concurrency bugs by inferring locking policies from failure inducing memory-access patterns. That is, we automatically identify memory-access patterns which are correlated with the manifestation of the bug, and then conjecture what is the intended locking policy of the program. Afterwards, we fix the program by implementing the locking policy so that the failure inducing memory-access patterns are made impossible. We have implemented our approach in a toolkit called PFix which supports Java programs. We applied PFix to a set of 23 concurrency bugs and are able to automatically fix 19 of them. In comparison, Grail which is the state-of-the-art tool for fixing concurrency bugs in Java programs can only fix 3 of them correctly.