content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.cassandra.gms;
  
  import org.apache.cassandra.locator.InetAddressAndPort;
  
  /**
   * An interface that provides an application with the ability
   * to query liveness information of a node in the cluster. It
   * also exposes methods which help an application register callbacks
   * for notifications of liveness information of nodes.
   */
  
  public interface IFailureDetector
  {
      /**
       * Failure Detector's knowledge of whether a node is up or
       * down.
       *
       * @param ep endpoint in question.
       * @return true if UP and false if DOWN.
       */
      public boolean isAlive(InetAddressAndPort ep);
  
      /**
       * This method is invoked by any entity wanting to interrogate the status of an endpoint.
       * In our case it would be the Gossiper. The Failure Detector will then calculate Phi and
       * deem an endpoint as suspicious or alive as explained in the Hayashibara paper.
       *
       * param ep endpoint for which we interpret the inter arrival times.
       */
      public void interpret(InetAddressAndPort ep);
  
      /**
       * This method is invoked by the receiver of the heartbeat. In our case it would be
       * the Gossiper. Gossiper inform the Failure Detector on receipt of a heartbeat. The
       * FailureDetector will then sample the arrival time as explained in the paper.
       *
       * param ep endpoint being reported.
       */
      public void report(InetAddressAndPort ep);
  
      /**
       * remove endpoint from failure detector
       */
      public void remove(InetAddressAndPort ep);
  
      /**
       * force conviction of endpoint in the failure detector
       */
      public void forceConviction(InetAddressAndPort ep);
  
      /**
       * Register interest for Failure Detector events.
       *
       * @param listener implementation of an application provided IFailureDetectionEventListener
       */
      public void registerFailureDetectionEventListener(IFailureDetectionEventListener listener);
  
      /**
       * Un-register interest for Failure Detector events.
       *
       * @param listener implementation of an application provided IFailureDetectionEventListener
       */
      public void unregisterFailureDetectionEventListener(IFailureDetectionEventListener listener);
  }
  