On the Usefulness of Liveness for Garbage Collection and Leak Detection

The effectiveness of garbage collectors and leak detectors in identifying dead objects depends on the “accuracy” of their reachability traversal. Accuracy has two orthogonal dimensions: (i) whether the reachability traversal can distinguish between pointers and non-pointers (type accuracy), and (ii) whether the reachability traversal can identify memory locations that will be dereferenced in the future (liveness accuracy). While prior work has investigated the importance of type accuracy, there has been little work investigating the importance of liveness accuracy for garbage collection or leak detection. This paper presents an experimental study of the importance of liveness on the accuracy of the reachability traversal. We show that while liveness can significantly improve the effectiveness of a garbage collector or leak detector, the simpler liveness schemes are largely ineffective. One must analyze globals using an interprocedural analysis to get significant benefit.