Dynamic Error Remediation: A Case Study with Null Pointer Exceptions

Managed programming languages have improved the robustness of software by reducing some classes of errors. Despite these improvements, programs still contain errors. Even with help from existing static and dynamic analysis tools, the errors are often difficult to detect and can be even more difficult to successfully eliminate. This work introduces a new approach, called dynamic error remediation, that further improves the robustness of software, by tolerating some null pointer exceptions until a patch can be created to fix the exception. This paper describes dynamic error remediation, and its effectiveness, with different strategies for handling the exceptions. We show that dynamic error remediation is successful in allowing programs to continue execution and to do meaningful work in many cases. We then describe the bug suite created to test dynamic error remediation, as well as providing a methodology for creating other bug suites. Finally, we describe origin tracking, a JVM modification which exposes the origin of null values that cause null pointer exceptions. Because dynamic error remediation is successful in many cases, we assert that it is a viable strategy for increasing availability and reliability in many programs. While increasing availability over correctness is not ideal in all cases, we show that there are real examples where it is preferred, and we provide dynamic error remediation as a tool for developers and users to survive null pointer exception bugs.