void handleDeadWorker(ServerName workerName) {
    // resubmit the tasks on the TimeoutMonitor thread. Makes it easier
    // to reason about concurrency. Makes it easier to retry.
    synchronized (deadWorkersLock) {
      if (deadWorkers == null) {
        deadWorkers = new HashSet<>(100);
      }
      deadWorkers.add(workerName);
    }
    LOG.info("Dead splitlog worker {}", workerName);
  }
Returns null on success, existing task on error
hbase-server/src/main/java/org/apache/hadoop/hbase/master/SplitLogManager.java