LeaderInquireClient.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 tachyon;

import java.util.List;
import java.util.HashMap;

import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.log4j.Logger;
import org.apache.zookeeper.data.Stat;
import tachyon.util.CommonUtils;

/**
 * Utility to get leader from zookeeper.
 */
public class LeaderInquireClient {
  private static final int MAX_TRY = 10;

  public static synchronized LeaderInquireClient getClient(String zookeeperAddress,
      String leaderPath) {
    String key = zookeeperAddress + leaderPath;
    if (!createdClients.containsKey(key)) {
      createdClients.put(key, new LeaderInquireClient(zookeeperAddress, leaderPath));
    }
    return createdClients.get(key);
  }

  private final Logger LOG = Logger.getLogger(Constants.LOGGER_TYPE);
  private final String ZOOKEEPER_ADDRESS;
  private final String LEADER_PATH;

  private final CuratorFramework CLIENT;

  private static HashMap<String, LeaderInquireClient> createdClients =
      new HashMap<String, LeaderInquireClient>();

  private LeaderInquireClient(String zookeeperAddress, String leaderPath) {
    ZOOKEEPER_ADDRESS = zookeeperAddress;
    LEADER_PATH = leaderPath;

    CLIENT =
        CuratorFrameworkFactory.newClient(ZOOKEEPER_ADDRESS, new ExponentialBackoffRetry(Constants.SECOND_MS, 3));
    CLIENT.start();
  }

  public synchronized String getMasterAddress() {
    int tried = 0;
    try {
      while (tried < MAX_TRY) {
        if (CLIENT.checkExists().forPath(LEADER_PATH) != null) {
          List<String> masters = CLIENT.getChildren().forPath(LEADER_PATH);
          LOG.info(masters);
          if (masters.size() >= 1) {
            if (masters.size() == 1) {
              return masters.get(0);
            }

            long maxTime = 0;
            String leader = "";
            for (String master : masters) {
              Stat stat = CLIENT.checkExists().forPath(CommonUtils.concat(LEADER_PATH, master));
              if (stat != null && stat.getCtime() > maxTime) {
                maxTime = stat.getCtime();
                leader = master;
              }
            }
            return leader;
          }
        } else {
          LOG.info(LEADER_PATH + " does not exist (" + (++ tried) + ")");
        }
        CommonUtils.sleepMs(LOG, Constants.SECOND_MS);
      }
    } catch (Exception e) {
      LOG.error(e.getMessage(), e);
    }

    return null;
  }
}