code: public void restoreAfterSafeModeRestart() {
      // Put the sessionsToCtxFromDisk entries into their respective
      // SessionNotifierThreads instances
      for (Map.Entry<String, SessionNotificationCtx> entry :
            sessionsToCtxFromDisk.entrySet()) {
        // The conf and the conf related properties are missing in the
        // sessionsToCtx objects
        entry.getValue().setConf(conf);
        handleToNotifier(entry.getKey()).sessionsToCtx.put(entry.getKey(),
                                                            entry.getValue());
        sessionsToCtxFromDisk.remove(entry);
      }
  
      // Put the deletedSessions into the the respective SessionNotifierThreads
      for (String deletedSessionHandle : deletedSessionsFromDisk) {
        SessionNotifierThread notifierThread =
          handleToNotifier(deletedSessionHandle);
        if (notifierThread.sessionsToCtx.get(deletedSessionHandle) != null) {
          notifierThread.deletedSessions.put(deletedSessionHandle,
                                              notifierThread);
        }
        deletedSessionsFromDisk.remove(deletedSessionHandle);
      }
  
      // We can now start the notifier threads
      for (int i = 0; i < numNotifierThreads; i++) {
        notifierThreads[i].start();
      }
    }
docs: This method rebuilds members related to the SessionNotifier instance,
  which were not directly persisted themselves.