The java processes spawned by our Lucene nightly benchmarks sometimes randomly hang, apparently while loading classes across threads, under contention.
It is rare, maybe once a week in the nightly benchmarks (which spawn many java processes with many threads across 128 CPU cores). It is clearly a deadlock – when it strikes, the process hangs forever until I notice and kill -9 it. I posted a coupled jstacks in the issue above.
Robert Muir suggested using classcycle to maybe statically dig into possible deadlocks ... I have not tried that yet.