code: public static void registerShutdownHook(int priority, boolean runOnCrash, Runnable action)
      {
          m_instance.addHook(priority, runOnCrash, action);
          //Any hook registered lets print crash messsage.
          ShutdownHooks.m_crashMessage = true;
      }
docs: Register an action to be run when the JVM exits.
  @param priority The priority level at which this action should be run.  Lower values will run earlier.
  @param runOnCrash  Whether or not this action should be performed if the server is shutting down
  due to a call to crashVoltDB()
  @param action   A Runnable containing the action to be run on shutdown.