Exception-handling bugs in java and a language extension to avoid them

Abstract. It is difficult to write programs that behave correctly in the presence of exceptions. We describe a dataflow analysis for finding a cer-tain class of mistakes made while programs handle exceptions. These mistakes involve resource leaks and failures to restore program-specific invariants. Using this analysis we have found over 1,200 bugs in 4 million lines of Java. We give some evidence of the importance of the bugs we found and use them to highlight some limitations of destructors and final-izers. We propose and evaluate a new language feature, the compensation stack, to make it easier to write solid code in the presence of exceptions. These compensation stacks track obligations and invariants at run-time. Two case studies demonstrate that they can yield more natural source code and more consistent behavior in long-running programs.