Leak pruning

Abstract

Managed languages improve programmer productivity with type safety and garbage collection, which eliminate memory errors such as dangling pointers, double frees, and buffer overflows. However, because garbage collection uses reachability to over-approximate live objects, programs may still leak memory if programmers forget to eliminate the last reference to an object that will not be used again. Leaks slow programs by increasing collector workload and frequency. Growing leaks eventually crash programs. This paper introduces leak pruning, which keeps programs running by predicting and reclaiming leaked objects at run time. It predicts dead objects and reclaims them based on observing data structure usage patterns. Leak pruning preserves semantics because it waits for heap exhaustion before reclaiming objects and poisons references to objects it reclaims. If the program later tries to access a poisoned reference, the virtual machine (VM) throws an error. We show leak pruning has low overhead in a Java VM and evaluate it on 10 leaking programs. Leak pruning does not help two programs, executes five substantial programs 1.6-81X longer, and executes three programs, including a leak in Eclipse, for at least 24 hours. In the worst case, leak pruning defers fatal errors. In the best case, it keeps leaky programs running with preserved semantics and consistent throughput.