Utilizing object reference graphs and garbage collection roots to detect memory leaks in offline memory monitoring

Complex software systems often suffer from performance problems caused by memory anomalies such as memory leaks. While the proliferation of objects is rather easy to detect using state-of-the-art memory monitoring tools, extracting a leak's root cause, i.e., identifying the objects that keep the accumulating objects alive, is still poorly supported. Most state-of-the-art tools rely on the dominator tree of the object graph and thus only support single-object ownership analysis. Multi-object ownership analysis, e.g., when the leaking objects are contained in multiple collections, is not possible by merely relying on the dominator tree. We present an efficient approach to continuously collect GC root information (e.g., static fields or thread-local variables) in a trace-based memory monitoring tool, as well as algorithms that use this information to calculate the transitive closure (i.e., all reachable objects) and the GC closure (i.e., objects that are kept alive) for arbitrary heap object groups. These closures allow to derive various metrics for heap object groups that can be used to guide the user during memory leak analysis. We implemented our approach in AntTracks, an offline memory monitoring tool, and demonstrate its usefulness by comparing it with other widely used tools for memory leak detection such as the Eclipse Memory Analyzer. Our evaluation shows that collecting GC root information tracing introduces about 1% overhead, in terms of run time as well as trace file size.