geode-core/src/main/java/org/apache/geode/distributed/internal/MembershipListener.java

/*
 * 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.geode.distributed.internal;

import java.util.List;
import java.util.Set;

import org.apache.geode.distributed.internal.membership.InternalDistributedMember;

/**
 * This interface specifies callback methods that are invoked when remote GemFire systems enter and
 * exit the distributed cache. Note that a {@code MembershipListener} can be added from any VM,
 * but the callback methods are always invoked in the GemFire manager VM. Thus, the callback methods
 * should not perform time-consuming operations.
 *
 * @see ClusterDistributionManager#addMembershipListener
 */
public interface MembershipListener {

  /**
   * This method is invoked when a new member joins the system
   *
   * @param distributionManager that is calling this listener
   * @param id The id of the new member that has joined the system
   */
  default void memberJoined(DistributionManager distributionManager, InternalDistributedMember id) {
    // implement if needed
  }

  /**
   * This method is invoked after a member has explicitly left the system. It may not get invoked if
   * a member becomes unreachable due to crash or network problems.
   *
   * @param distributionManager that is calling this listener
   * @param id The id of the new member that has joined the system
   * @param crashed True if member did not depart in an orderly manner.
   */
  default void memberDeparted(DistributionManager distributionManager, InternalDistributedMember id,
      boolean crashed) {
    // implement if needed
  }

  /**
   * This method is invoked after the group membership service has suspected that a member is no
   * longer alive, but has not yet been removed from the membership view
   *
   * @param distributionManager that is calling this listener
   * @param id the suspected member
   * @param whoSuspected the member that initiated suspect processing
   * @param reason the reason the member was suspected
   */
  default void memberSuspect(DistributionManager distributionManager, InternalDistributedMember id,
      InternalDistributedMember whoSuspected, String reason) {
    // implement if needed
  }

  /**
   * This is notification that more than 50% of member weight has been lost in a single view change.
   * Notification is performed before the view has been installed.
   *
   * @param distributionManager that is calling this listener
   * @param failures members that have been lost
   * @param remaining members that remain
   */
  default void quorumLost(DistributionManager distributionManager,
      Set<InternalDistributedMember> failures,
      List<InternalDistributedMember> remaining) {
    // implement if needed
  }
}