Major Description
Currently we don't track LearnerHandler threads in leader; we rely on the socket timeout to raise an exception and use that exception as a signal to let the LearnerHandler thread kills itself. In cases where the learners restarts, if the time between restart beginning to finishing is less than the socket timeout value (currently hardcoded as initLimit * tickTime), then there will be no exception raised and the previous LearnerHandler thread corresponding to this learner will leak.
I have a test case and a proposed fix which I will submit later.