Evaluating Finalization-Based Object Lifetime Profiling

Using object lifetime information enables performance improvement through memory optimizations such as pretenuring and tuning garbage collector parameters. However, profiling object lifetimes is nontrivial and often requires a specialized virtual machine to instrument object allocations and dereferences. Alternative lifetime profiling could be done with less implementation effort using available finalization mechanisms such as weak references. In this paper, we study the impact of finalization on object lifetime profiling. We built an actionable lifetime profiler using the ephemeron finalization mechanism named FiLiP. FiLiP instruments object allocations to exactly record an object’s allocation time and it attaches an ephemeron to each allocated object to capture its finalization time. We show that FiLiP can be used in practice and achieves a significant overhead reduction by pretenuring the ephemeron objects. We further experiment with the impact of sampling object allocations, showing that sampling further reduces profiling overhead while still maintaining actionable lifetime measurements.