/**
* 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 com.google.common.collect.Lists;
import org.apache.curator.utils.CloseableUtils;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.test.TestingServer;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.List;
public class LeaderSelectorExample
{
private static final int CLIENT_QTY = 3;
private static final String PATH = "/examples/leader";
public static void main(String[] args) throws Exception
{
// all of the useful sample code is in ExampleClient.java
System.out.println("Create " + CLIENT_QTY + " clients, have each negotiate for leadership and then wait a random number of seconds before letting another leader election occur.");
System.out.println("Notice that leader election is fair: all clients will become leader and will do so the same number of times.");
List<CuratorFramework> clients = Lists.newArrayList();
List<ExampleClient> examples = Lists.newArrayList();
TestingServer server = new TestingServer();
try
{
for ( int i = 5; i < 7; ++i )
{
CuratorFramework client = CuratorFrameworkFactory.
newClient(server.getConnectString(), new ExponentialBackoffRetry(1000, 3));
clients.add(client);
ExampleClient example = new ExampleClient(client, PATH, "Client==== #" + i);
examples.add(example);
client.start();
example.start();
}
for ( int i = 1; i < 3; ++i )
{
CuratorFramework client2 = CuratorFrameworkFactory.newClient(server.getConnectString(), new ExponentialBackoffRetry(1000, 3));
clients.add(client2);
ExampleClient example = new ExampleClient(client2, PATH, "Client==== #" + i);
examples.add(example);
client2.start();
example.start();
}
System.out.println("Press enter/return to quit\n");
new BufferedReader(new InputStreamReader(System.in)).readLine();
}
finally
{
System.out.println("Shutting down...");
for ( ExampleClient exampleClient : examples )
{
CloseableUtils.closeQuietly(exampleClient);
}
for ( CuratorFramework client : clients )
{
CloseableUtils.closeQuietly(client);
}
CloseableUtils.closeQuietly(server);
}
}
}
package leader;
import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.recipes.leader.LeaderSelector;
import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;
/**
* An example leader selector client. Note that {@link LeaderSelectorListenerAdapter} which
* has the recommended handling for connection state issues
*/
public class ExampleClient extends LeaderSelectorListenerAdapter implements Closeable
{
private final String name;
private final LeaderSelector leaderSelector;
private final AtomicInteger leaderCount = new AtomicInteger();
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();
}
public void close() throws IOException
{
leaderSelector.close();
}
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;
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
{
System.out.println(name + " relinquishing leadership.\n");
}
}
}