To help with analyzing fork-heavy scenarios, it would help if we could see at one glance which process a process reaper thread is waiting on. A pragmatic way would be to add the pid to its name - that way, e.g. thread dumps with lots of reaper threads would be more enlightening.

Since reaper threads get reused, we would have to change the name back to some base name when the reaper is done with the process. This has the additional benefit of showing us in the thread dump which reapers are actually reaping, and which are just ideling around (admittedly, the callstack can be user for that too, but with a pid showing one could grep a thread dump and see immediately which processes were forked by this VM).