It is difficult to write programs that behave correctly in the presence of run-time errors. Proper behavior in the face of exceptional situations is important to the reliability of long-running programs. Existing programming language features often provide poor support for executing clean-up code and for restoring invariants. We present a data-flow analysis for finding a certain class of exception-handling defects: those related to a failure to release resources or to clean up properly along all paths. Many real-world programs violate such resource usage rules because of incorrect exception handling. Our flow-sensitive analysis keeps track of outstanding obligations along program paths and does a precise modeling of control flow in the presence of exceptions. Using it, we have found over 1,300 exception handling defects in over 5 million lines of Java code. Based on those defects we propose a programming language feature, the compensation stack, that keeps track of obligations at run time and ensures that they are discharged. We present a type system for compensation stacks that tracks collections of obligations. Finally, we present case studies to demonstrate that this feature is natural, efficient, and can improve reliability.

Exceptional Situations and Program Reliability, Westley Weimer and George C. Necula, ACM Trans. Program. Lang. Syst., 2008.