storm-client/src/jvm/org/apache/storm/nimbus/ILeaderElector.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.storm.nimbus;

import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import org.apache.storm.shade.com.google.common.annotations.VisibleForTesting;

/**
 * The interface for leader election.
 */
public interface ILeaderElector extends AutoCloseable {

    /**
     * Method guaranteed to be called as part of initialization of leader elector instance.
     * @param conf configuration
     */
    void prepare(Map<String, Object> conf);

    /**
     * queue up for leadership lock. The call returns immediately and the caller must
     * check isLeader() to perform any leadership action. This method can be called
     * multiple times so it needs to be idempotent.
     */
    void addToLeaderLockQueue() throws Exception;

    /**
     * Removes the caller from leadership election, relinquishing leadership if acquired, then requeues for leadership after the specified
     * delay.
     * @param delayMs The delay to wait before re-entering the election
     */
    void quitElectionFor(int delayMs) throws Exception;

    /**
     * Decide if the caller currently has the leader lock.
     * @return true if the caller currently has the leader lock.
     */
    boolean isLeader() throws Exception;

    /**
     * Get the current leader's address.
     * @return the current leader's address, may return null if no one has the lock.
     */
    NimbusInfo getLeader();
    
    /**
     * Wait for the caller to gain leadership. This should only be used in single-Nimbus clusters, and is only useful to allow testing
     * code to wait for a LocalCluster's Nimbus to gain leadership before trying to submit topologies.
     *
     * @return true is leadership was acquired, false otherwise
     */
    @VisibleForTesting
    boolean awaitLeadership(long timeout, TimeUnit timeUnit) throws InterruptedException;

    /**
     * Get list of current nimbus addresses.
     * @return list of current nimbus addresses, includes leader.
     */
    List<NimbusInfo> getAllNimbuses() throws Exception;

    /**
     * Method called to allow for cleanup. Relinquishes leadership if owned by the caller.
     */
    @Override
    void close() throws Exception;
}