Why Did This Reviewed Code Crash? An Empirical Study of Mozilla Firefox

Code review, i.e., the practice of having other team members critique changes to a software system, is a pillar of modern software quality assurance approaches. Although this activity aims at improving software quality, some high-impact defects, such as crash-related defects, can elude the inspection of reviewers and escape to the field, affecting user satisfaction and increasing maintenance overhead. In this research, we investigate the characteristics of crash-prone code, observing that such code tends to have high complexity and depend on many other classes. In the code review process, developers often spend a long time on and have long discussions about crash-prone code. We manually classify a sample of reviewed crash-prone patches according to their purposes and root causes. We observe that most crash-prone patches aim to improve performance, refactor code, add functionality, or fix previous crashes. Memory and semantic errors are identified as major root causes of the crashes. Our results suggest that software organizations should apply more scrutiny to these types of patches, and provide better support for reviewers to focus their inspection effort by using static analysis tools.