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 com.alibaba.wasp.zookeeper;
  
  import com.alibaba.wasp.ServerName;
  import com.alibaba.wasp.master.FServerManager;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.Abortable;
  import org.apache.zookeeper.KeeperException;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.NavigableSet;
  import java.util.TreeSet;
  
  /**
   * Tracks the online fservers via ZK.
   * 
   * <p>
   * Handling of new RSs checking in is done via RPC. This class is only
   * responsible for watching for expired nodes. It handles listening for changes
   * in the RS node list and watching each node.
   * 
   * <p>
   * If an FS node gets deleted, this automatically handles calling of
   * {@link com.alibaba.wasp.master.FServerManager#expireServer(com.alibaba.wasp.ServerName)}
   */
  public class FServerTracker extends ZooKeeperListener {
    protected static final Log LOG = LogFactory.getLog(FServerTracker.class);
    private NavigableSet<ServerName> fservers = new TreeSet<ServerName>();
    private FServerManager serverManager;
    private Abortable abortable;
  
    public FServerTracker(ZooKeeperWatcher watcher, Abortable abortable,
        FServerManager serverManager) {
      super(watcher);
      this.abortable = abortable;
      this.serverManager = serverManager;
    }
  
    /**
     * Starts the tracking of online FServers.
     *
     * <p>
     * All RSs will be tracked after this method is called.
     *
     * @throws org.apache.zookeeper.KeeperException
     * @throws java.io.IOException
     */
    public void start() throws KeeperException, IOException {
      watcher.registerListener(this);
      List<String> servers = ZKUtil.listChildrenAndWatchThem(watcher,
          watcher.fsZNode);
      add(servers);
    }
  
    protected void add(final List<String> servers) throws IOException {
      synchronized (this.fservers) {
        this.fservers.clear();
        for (String n : servers) {
          ServerName sn = ServerName.parseServerName(ZKUtil.getNodeName(n));
          this.fservers.add(sn);
        }
      }
    }
  
    protected void remove(final ServerName sn) {
      synchronized (this.fservers) {
        this.fservers.remove(sn);
      }
    }
  
    @Override
    public void nodeDeleted(String path) {
      if (path.startsWith(watcher.fsZNode)) {
        String serverName = ZKUtil.getNodeName(path);
        LOG.info("FServer ephemeral node deleted, processing expiration ["
            + serverName + "]");
        ServerName sn = ServerName.parseServerName(serverName);
        if (!serverManager.isServerOnline(sn)) {
          LOG.warn(serverName.toString()
              + " is not online or isn't known to the master."
              + "The latter could be caused by a DNS misconfiguration.");
          return;
        }
        remove(sn);
        this.serverManager.expireServer(sn);
      }
    }
  
    @Override
    public void nodeChildrenChanged(String path) {
      if (path.equals(watcher.fsZNode)) {
        try {
          List<String> servers = ZKUtil.listChildrenAndWatchThem(watcher,
              watcher.fsZNode);
          add(servers);
        } catch (IOException e) {
          abortable.abort("Unexpected zk exception getting RS nodes", e);
        } catch (KeeperException e) {
          abortable.abort("Unexpected zk exception getting RS nodes", e);
        }
      }
    }
  
    /**
     * Gets the online servers.
     * 
     * @return list of online servers
     */
    public List<ServerName> getOnlineServers() {
      synchronized (this.fservers) {
        return new ArrayList<ServerName>(this.fservers);
      }
    }
  }
  