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Leader Election Pattern (#923)
* Fix issue #761: ThreadSafeDoubleCheckLocking.java: Instantiating by Reflection call will be successful if you do that firstly * Create leader election module * Create Interface of Instance and MessageManager * Create implementations with token ring algorithm * Change package structure. Create basic message system. * Implement heartbeat and heartbeat invoking message system * Implement election message handler * Add leader message handler * Add main entry point * Add comments * Update README.md * Fix checkstyle issue * Add Unit Tests * Add Unit Tests * Add bully leader selection * Change System.out to log print. Add MIT license in each file. * Add More java doc comments * Add unit test * Add unit tests
This commit is contained in:
Azureyjt
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/**
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* The MIT License
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* Copyright (c) 2014-2016 Ilkka Seppälä
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* <p>
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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* <p>
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* <p>
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.leaderelection.bully;
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import com.iluwatar.leaderelection.Instance;
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import com.iluwatar.leaderelection.Message;
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import com.iluwatar.leaderelection.MessageManager;
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import com.iluwatar.leaderelection.MessageType;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* Example of how to use bully leader election. Initially 5 instances is created in the clould
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* system, and the instance with ID 1 is set as leader. After the system is started stop the
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* leader instance, and the new leader will be elected.
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*/
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public class BullyApp {
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/**
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* Program entry point
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*/
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public static void main(String[] args) {
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Map<Integer, Instance> instanceMap = new HashMap<>();
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MessageManager messageManager = new BullyMessageManager(instanceMap);
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BullyInstance instance1 = new BullyInstance(messageManager, 1, 1);
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BullyInstance instance2 = new BullyInstance(messageManager, 2, 1);
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BullyInstance instance3 = new BullyInstance(messageManager, 3, 1);
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BullyInstance instance4 = new BullyInstance(messageManager, 4, 1);
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BullyInstance instance5 = new BullyInstance(messageManager, 5, 1);
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instanceMap.put(1, instance1);
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instanceMap.put(2, instance2);
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instanceMap.put(3, instance3);
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instanceMap.put(4, instance4);
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instanceMap.put(5, instance5);
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instance4.onMessage(new Message(MessageType.HEARTBEAT_INVOKE, ""));
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Thread thread1 = new Thread(instance1);
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Thread thread2 = new Thread(instance2);
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Thread thread3 = new Thread(instance3);
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Thread thread4 = new Thread(instance4);
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Thread thread5 = new Thread(instance5);
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thread1.start();
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thread2.start();
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thread3.start();
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thread4.start();
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thread5.start();
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instance1.setAlive(false);
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}
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}
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/**
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* The MIT License
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* Copyright (c) 2014-2016 Ilkka Seppälä
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* <p>
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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* <p>
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* <p>
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.leaderelection.bully;
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import com.iluwatar.leaderelection.AbstractInstance;
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import com.iluwatar.leaderelection.Message;
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import com.iluwatar.leaderelection.MessageManager;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* Impelemetation with bully algorithm. Each instance should have a sequential id and is able to
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* communicate with other instances in the system. Initially the instance with smallest (or largest)
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* ID is selected to be the leader. All the other instances send heartbeat message to leader periodically
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* to check its health. If one certain instance finds the server done, it will send an election message
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* to all the instances of which the ID is larger. If the target instance is alive, it will return an
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* alive message (in this sample return true) and then send election message with its ID. If not,
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* the original instance will send leader message to all the other instances.
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*/
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public class BullyInstance extends AbstractInstance {
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private static final Logger LOGGER = LoggerFactory.getLogger(BullyInstance.class);
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/**
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* Constructor of BullyInstance.
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*/
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public BullyInstance(MessageManager messageManager, int localId, int leaderId) {
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super(messageManager, localId, leaderId);
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}
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/**
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* Process the heartbeat invoke message. After receiving the message, the instance will send a heartbeat
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* to leader to check its health. If alive, it will inform the next instance to do the heartbeat. If not,
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* it will start the election process.
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*/
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@Override
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protected void handleHeartbeatInvokeMessage() {
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try {
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boolean isLeaderAlive = messageManager.sendHeartbeatMessage(leaderId);
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if (isLeaderAlive) {
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LOGGER.info("Instance " + localId + "- Leader is alive.");
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Thread.sleep(HEARTBEAT_INTERVAL);
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messageManager.sendHeartbeatInvokeMessage(localId);
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} else {
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LOGGER.info("Instance " + localId + "- Leader is not alive. Start election.");
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boolean electionResult = messageManager.sendElectionMessage(localId, String.valueOf(localId));
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if (electionResult) {
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LOGGER.info("Instance " + localId + "- Succeed in election. Start leader notification.");
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messageManager.sendLeaderMessage(localId, localId);
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}
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}
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} catch (InterruptedException e) {
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LOGGER.info("Instance " + localId + "- Interrupted.");
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}
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}
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/**
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* Process election invoke message. Send election message to all the instances with smaller ID. If any
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* one of them is alive, do nothing. If no instance alive, send leader message to all the alive instance
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* and restart heartbeat.
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*/
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@Override
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protected void handleElectionInvokeMessage() {
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if (!isLeader()) {
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LOGGER.info("Instance " + localId + "- Start election.");
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boolean electionResult = messageManager.sendElectionMessage(localId, String.valueOf(localId));
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if (electionResult) {
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LOGGER.info("Instance " + localId + "- Succeed in election. Start leader notification.");
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leaderId = localId;
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messageManager.sendLeaderMessage(localId, localId);
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messageManager.sendHeartbeatInvokeMessage(localId);
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}
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}
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}
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/**
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* Process leader message. Update local leader information.
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*/
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@Override
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protected void handleLeaderMessage(Message message) {
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leaderId = Integer.valueOf(message.getContent());
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LOGGER.info("Instance " + localId + " - Leader update done.");
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}
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private boolean isLeader() {
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return localId == leaderId;
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}
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/**
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* Not used in Bully instance.
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*/
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@Override
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protected void handleLeaderInvokeMessage() {}
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@Override
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protected void handleHeartbeatMessage(Message message) {}
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@Override
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protected void handleElectionMessage(Message message) {}
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}
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+117
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/**
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* The MIT License
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* Copyright (c) 2014-2016 Ilkka Seppälä
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* <p>
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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* <p>
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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* <p>
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.leaderelection.bully;
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import com.iluwatar.leaderelection.AbstractMessageManager;
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import com.iluwatar.leaderelection.Instance;
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import com.iluwatar.leaderelection.Message;
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import com.iluwatar.leaderelection.MessageType;
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import java.util.List;
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import java.util.Map;
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import java.util.stream.Collectors;
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/**
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* Implementation of BullyMessageManager
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*/
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public class BullyMessageManager extends AbstractMessageManager {
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/**
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* Constructor of BullyMessageManager.
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*/
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public BullyMessageManager(Map<Integer, Instance> instanceMap) {
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super(instanceMap);
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}
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/**
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* Send heartbeat message to current leader instance to check the health.
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* @param leaderId leaderID
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* @return {@code true} if the leader is alive.
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*/
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@Override
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public boolean sendHeartbeatMessage(int leaderId) {
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Instance leaderInstance = instanceMap.get(leaderId);
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boolean alive = leaderInstance.isAlive();
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return alive;
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}
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/**
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* Send election message to all the instances with smaller ID.
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* @param currentId Instance ID of which sends this message.
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* @param content Election message content.
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* @return {@code true} if no alive instance has smaller ID, so that the election is accepted.
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*/
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@Override
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public boolean sendElectionMessage(int currentId, String content) {
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List<Integer> candidateList = findElectionCandidateInstanceList(currentId);
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if (candidateList.isEmpty()) {
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return true;
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} else {
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Message electionMessage = new Message(MessageType.ELECTION_INVOKE, "");
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candidateList.stream()
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.forEach((i) -> instanceMap.get(i).onMessage(electionMessage));
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return false;
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}
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}
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/**
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* Send leader message to all the instances to notify the new leader.
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* @param currentId Instance ID of which sends this message.
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* @param leaderId Leader message content.
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* @return {@code true} if the message is accepted.
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*/
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@Override
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public boolean sendLeaderMessage(int currentId, int leaderId) {
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Message leaderMessage = new Message(MessageType.LEADER, String.valueOf(leaderId));
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instanceMap.keySet()
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.stream()
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.filter((i) -> i != currentId)
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.forEach((i) -> instanceMap.get(i).onMessage(leaderMessage));
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return false;
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}
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/**
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* Send heartbeat invoke message to the next instance.
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* @param currentId Instance ID of which sends this message.
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*/
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@Override
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public void sendHeartbeatInvokeMessage(int currentId) {
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Instance nextInstance = this.findNextInstance(currentId);
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Message heartbeatInvokeMessage = new Message(MessageType.HEARTBEAT_INVOKE, "");
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nextInstance.onMessage(heartbeatInvokeMessage);
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}
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/**
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* Find all the alive instances with smaller ID than current instance.
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* @param currentId ID of current instance.
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* @return ID list of all the candidate instance.
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*/
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private List<Integer> findElectionCandidateInstanceList(int currentId) {
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return instanceMap.keySet()
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.stream()
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.filter((i) -> i < currentId && instanceMap.get(i).isAlive())
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.collect(Collectors.toList());
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}
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}
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