/**
* 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.DeserializationException;
import com.alibaba.wasp.ServerName;
import org.apache.hadoop.hbase.Abortable;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
/**
* Manages the location of the current active FMaster for the FServer.
* <p>
* Listens for ZooKeeper events related to the master address. The node
* <code>/master</code> will contain the address of the current master. This
* listener is interested in <code>NodeDeleted</code> and
* <code>NodeCreated</code> events on <code>/master</code>.
* <p>
* Utilizes {@link ZooKeeperNodeTracker} for zk interactions.
* <p>
* You can get the current master via {@link #getMasterAddress()} or via
* {@link #getMasterAddress(ZooKeeperWatcher)} if you do not have a running
* instance of this Tracker in your context.
* <p>
* This class also includes utility for interacting with the master znode, for
* writing and reading the znode content.
*/
public class MasterAddressTracker extends ZooKeeperNodeTracker {
/**
* Construct a master address listener with the specified
* <code>zookeeper</code> reference.
* <p>
* This constructor does not trigger any actions, you must call methods
* explicitly. Normally you will just want to execute {@link #start()} to
* begin tracking of the master address.
*
* @param watcher
* zk reference and watcher
* @param abortable
* abortable in case of fatal error
*/
public MasterAddressTracker(ZooKeeperWatcher watcher, Abortable abortable) {
super(watcher, watcher.getMasterAddressZNode(), abortable);
}
/**
* Get the address of the current master if one is available. Returns null if
* no current master.
*
* @return Server name or null if timed out.
*/
public ServerName getMasterAddress() {
return getMasterAddress(false);
}
/**
* Get the address of the current master if one is available. Returns null if
* no current master. If refresh is set, try to load the data from ZK again,
* otherwise, cached data will be used.
*
* @param refresh
* whether to refresh the data by calling ZK directly.
* @return Server name or null if timed out.
*/
public ServerName getMasterAddress(final boolean refresh) {
try {
return ServerName.parseFrom(super.getData(refresh));
} catch (DeserializationException e) {
LOG.warn("Failed parse", e);
return null;
}
}
/**
* Get master address. Use this instead of {@link #getMasterAddress()} if you
* do not have an instance of this tracker in your context.
*
* @param zkw
* ZooKeeperWatcher to use
* @return ServerName stored in the the master address znode or null if no
* znode present.
* @throws org.apache.zookeeper.KeeperException
* @throws java.io.IOException
*/
public static ServerName getMasterAddress(final ZooKeeperWatcher zkw)
throws KeeperException, IOException {
byte[] data = ZKUtil.getData(zkw, zkw.getMasterAddressZNode());
if (data == null) {
throw new IOException(
"Can't get master address from ZooKeeper; znode data == null");
}
try {
return ServerName.parseFrom(data);
} catch (DeserializationException e) {
KeeperException ke = new KeeperException.DataInconsistencyException();
ke.initCause(e);
throw ke;
}
}
/**
* Set master address into the <code>master</code> znode or into the backup
* subdirectory of backup masters; switch off the passed in <code>znode</code>
* path.
*
* @param zkw
* The ZooKeeperWatcher to use.
* @param znode
* Where to create the znode; could be at the top level or it could
* be under backup masters
* @param master
* ServerName of the current master
* @return true if node created, false if not; a watch is set in both cases
* @throws org.apache.zookeeper.KeeperException
*/
public static boolean setMasterAddress(final ZooKeeperWatcher zkw,
final String znode, final ServerName master) throws KeeperException {
return ZKUtil.createEphemeralNodeAndWatch(zkw, znode, toByteArray(master));
}
/**
* Check if there is a master available.
*
* @return true if there is a master set, false if not.
*/
public boolean hasMaster() {
return super.getData(false) != null;
}
/**
* @param sn
* @return Content of the master znode as a serialized pb with the pb magic as
* prefix.
*/
static byte[] toByteArray(final ServerName sn) {
return sn.toByte();
}
/**
* delete the master znode if its content is same as the parameter
*/
public static boolean deleteIfEquals(ZooKeeperWatcher zkw,
final String content) {
if (content == null) {
throw new IllegalArgumentException("Content must not be null");
}
try {
Stat stat = new Stat();
byte[] data = ZKUtil.getDataNoWatch(zkw, zkw.getMasterAddressZNode(),
stat);
ServerName sn = ServerName.parseFrom(data);
if (sn != null && content.equals(sn.toString())) {
return (ZKUtil.deleteNode(zkw, zkw.getMasterAddressZNode(),
stat.getVersion()));
}
} catch (KeeperException e) {
LOG.warn("Can't get or delete the master znode", e);
} catch (DeserializationException e) {
LOG.warn("Can't get or delete the master znode", e);
}
return false;
}
}