/**
* 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 leader;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.recipes.leader.LeaderSelector;
import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;
import org.apache.curator.framework.state.ConnectionState;
import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
/**
* An example leader selector client
*/
public class ExampleClient implements Closeable, LeaderSelectorListener
{
private final String name;
private final LeaderSelector leaderSelector;
private final AtomicInteger leaderCount = new AtomicInteger();
private volatile Thread ourThread = null;
public ExampleClient(CuratorFramework client, String path, String name)
{
this.name = name;
// create a leader selector using the given path for management
// all participants in a given leader selection must use the same path
// ExampleClient here is also a LeaderSelectorListener but this isn't required
leaderSelector = new LeaderSelector(client, path, this);
// for most cases you will want your instance to requeue when it relinquishes leadership
leaderSelector.autoRequeue();
}
public void start() throws IOException
{
// the selection for this instance doesn't start until the leader selector is started
// leader selection is done in the background so this call to leaderSelector.start() returns immediately
leaderSelector.start();
}
@Override
public void close() throws IOException
{
leaderSelector.close();
}
@Override
public void takeLeadership(CuratorFramework client) throws Exception
{
// we are now the leader. This method should not return until we want to relinquish leadership
final int waitSeconds = (int)(5 * Math.random()) + 1;
ourThread = Thread.currentThread();
System.out.println(name + " is now the leader. Waiting " + waitSeconds + " seconds...");
System.out.println(name + " has been leader " + leaderCount.getAndIncrement() + " time(s) before.");
try
{
Thread.sleep(TimeUnit.SECONDS.toMillis(waitSeconds));
}
catch ( InterruptedException e )
{
System.err.println(name + " was interrupted.");
Thread.currentThread().interrupt();
}
finally
{
ourThread = null;
System.out.println(name + " relinquishing leadership.\n");
}
}
@Override
public void stateChanged(CuratorFramework client, ConnectionState newState)
{
// you MUST handle connection state changes. This WILL happen in production code.
if ( (newState == ConnectionState.LOST) || (newState == ConnectionState.SUSPENDED) )
{
if ( ourThread != null )
{
ourThread.interrupt();
}
}
}
}