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A resource leak occurs when a program allocates a resource, such as a socket or file handle, but fails to deallocate it. Resource leaks cause resource starvation, slowdowns, and crashes. Previous techniques to prevent resource leaks are either unsound, imprecise, inapplicable to existing code, slow, or a combination of these. Static detection of resource leaks requires checking that de-allocation methods are always invoked on relevant objects before they become unreachable. Our key insight is that leak detection can be reduced to an accumulation problem, a class of typestate problems amenable to sound and modular checking without the need for a heavyweight, whole-program alias analysis. The precision of an accumulation analysis can be improved by computing targeted aliasing information, and we augmented our baseline checker with three such novel techniques: a lightweight ownership transfer system; a specialized resource alias analysis; and a system to create a fresh obligation when a non-final resource field is updated. Our approach occupies a unique slice of the design space: it is sound and runs relatively quickly (taking minutes on programs that a state-of-the-art approach took hours to analyze). We implemented our techniques for Java in an open-source tool called the Resource Leak Checker. The Resource Leak Checker revealed 49 real resource leaks in widely-deployed software. It scales well, has a manageable false positive rate (comparable to the high-confidence resource leak analysis built into the Eclipse IDE), and imposes only a small annotation burden (1/1500 LoC) for developers. |
