public TreeMap<Long, WorkerState> workerStates() throws Exception {
        try (ShutdownManager.Reference ref = shutdownManager.takeReference()) {
            return stateChangeExecutor.submit(new GetWorkerStates()).get();
        }
    }
Cleans up the resources associated with a worker.  Processed by the worker
cleanup thread pool.
trogdor/src/main/java/org/apache/kafka/trogdor/agent/WorkerManager.java