public void restart(DiscoveryNode masterNode, String reason) {
   synchronized (masterNodeMutex) {
     if (logger.isDebugEnabled()) {
       logger.debug(
           "[master] restarting fault detection against master [{}], reason [{}]",
           masterNode,
           reason);
     }
     innerStop();
     innerStart(masterNode);
   }
 }
 public void stop(String reason) {
   synchronized (masterNodeMutex) {
     if (masterNode != null) {
       if (logger.isDebugEnabled()) {
         logger.debug(
             "[master] stopping fault detection against master [{}], reason [{}]",
             masterNode,
             reason);
       }
     }
     innerStop();
   }
 }