TreeMap<String, Long> activeWorkerIds() {
            TreeMap<String, Long> activeWorkerIds = new TreeMap<>();
            for (Map.Entry<String, Long> entry : workerIds.entrySet()) {
                WorkerState workerState = workerStates.get(entry.getValue());
                if (!workerState.done()) {
                    activeWorkerIds.put(entry.getKey(), entry.getValue());
                }
            }
            return activeWorkerIds;
        }
If this is non-empty, a message describing how this task failed.
trogdor/src/main/java/org/apache/kafka/trogdor/coordinator/TaskManager.java