This is a rare case found by my colleague which really happened on our production env.
Thread may hang(or enter a infinite loop ) when try to call IdLock.getLockEntry(). Here is the case:
1. Thread1 owned the IdLock, while Thread2(the only one waiting) was waiting for it.
2. Thread1 called releaseLockEntry, it will set IdLock.locked = false, but since Thread2 was waiting, it won't call map.remove(entry.id)
3. While Thread1 was calling releaseLockEntry, Thread2 was interrupted. So no one will remove this IdLock from the map.
4. If another thread try to call getLockEntry on this IdLock， it will end up in a infinite loop. Since existing = map.putIfAbsent(entry.id, entry)) != null and existing.locked=false
It is hard to write a UT since it is a very rare race condition.