Your threadLocal prevents a thread from unlocking a lock taken by a different thread. That's not good, as there are legitimate uses for this scenario (some producer-consumer).
What I also dislike is silently ignoring the unlock request. If it's forbidden, then it should probably throw.
Anyway, you can what you did without any thread local just by using AtomicReference<Thread> (with the content being the locking thread, or null, if it's free).
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Should I?
