LeaderElectionCallback.java

/*
 * Copyright 2010 Outerthought bvba
 *
 * Licensed 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.lilyproject.util.zookeeper;

/**
 * Used by {@link LeaderElection} to notify when to become leader and when to step down as leader.
 *
 * <p>The callback methods are not called from within a ZooKeeper Watcher callback, so you do not have
 * to worry that they might take some time or that they should not perform ZooKeeper operations
 * by themselves.
 *
 * <p>The {@link #activateAsLeader()} and {@link #deactivateAsLeader()} will never be called
 * concurrently.
 *
 * <p>This callback is not called for every state change. If the state would switch multiple times
 * between leader and not-leader during the processing of this callback, there will be only one
 * call to this callback to bring it to the current state.
 */
public interface LeaderElectionCallback {
    void activateAsLeader() throws Exception;

    void deactivateAsLeader() throws Exception;
}