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Leader Election Pattern (#923)

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* 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 2019-10-08 23:29:59 +08:00 committed by Ilkka Seppälä
parent 41b8d80479
commit 90ea4506ca
22 changed files with 1719 additions and 0 deletions
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---
layout: pattern
title: Leader Election
folder: leader-election
permalink: /patterns/leader-election/
categories: Other
tags:
- Java
- Difficulty-Beginner
---
## Intent
Leader Election pattern is commonly used in cloud system design. It can help to ensure that task instances selec the leader instance correctly and do not conflict with each other, cause contention for shared resources, or inadvertently interfere with the work that other task instances are performing.
## Applicability
Use this pattern when
* the tasks in a distributed application, such as a cloud-hosted solution, require careful coordination and there is no natural leader.
Do not use this pattern when
* there is a natural leader or dedicated process that can always act as the leader. For example, it may be possible to implement a singleton process that coordinates the task instances. If this process fails or becomes unhealthy, the system can shut it down and restart it.
* the coordination between tasks can be easily achieved by using a more lightweight mechanism. For example, if several task instances simply require coordinated access to a shared resource, a preferable solution might be to use optimistic or pessimistic locking to control access to that resource.
## Real world examples
* [Raft Leader Election](https://github.com/ronenhamias/raft-leader-election)
## Credits
* [ Cloud Design Patterns: Prescriptive Architecture Guidance for Cloud Applications](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/dn568104(v=pandp.10))

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<?xml version="1.0" encoding="UTF-8"?>
<!--
The MIT License
Copyright (c) 2014-2016 Ilkka Seppälä
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THFE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
-->
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<artifactId>java-design-patterns</artifactId>
<groupId>com.iluwatar</groupId>
<version>1.22.0-SNAPSHOT</version>
</parent>
<artifactId>leader-election</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
</project>

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
/**
* Abstract class of all the instance implementation classes.
*/
public abstract class AbstractInstance implements Instance, Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(AbstractInstance.class);
protected static final int HEARTBEAT_INTERVAL = 5000;
protected MessageManager messageManager;
protected Queue<Message> messageQueue;
protected final int localId;
protected int leaderId;
protected boolean alive;
/**
* Constructor of BullyInstance.
*/
public AbstractInstance(MessageManager messageManager, int localId, int leaderId) {
this.messageManager = messageManager;
this.messageQueue = new ConcurrentLinkedQueue<>();
this.localId = localId;
this.leaderId = leaderId;
this.alive = true;
}
/**
* The instance will execute the message in its message queue periodically once it is alive.
*/
@Override
public void run() {
while (true) {
if (!this.messageQueue.isEmpty()) {
this.processMessage(this.messageQueue.remove());
}
}
}
/**
* Once messages are sent to the certain instance, it will firstly be added to the queue and wait to be executed.
* @param message Message sent by other instances
*/
@Override
public void onMessage(Message message) {
messageQueue.offer(message);
}
/**
* Check if the instance is alive or not.
* @return {@code true} if the instance is alive.
*/
@Override
public boolean isAlive() {
return alive;
}
/**
* Set the health status of the certain instance.
* @param alive {@code true} for alive.
*/
@Override
public void setAlive(boolean alive) {
this.alive = alive;
}
/**
* Process the message according to its type.
* @param message Message polled from queue.
*/
private void processMessage(Message message) {
switch (message.getType()) {
case ELECTION:
LOGGER.info("Instance " + localId + " - Election Message handling...");
handleElectionMessage(message);
break;
case LEADER:
LOGGER.info("Instance " + localId + " - Leader Message handling...");
handleLeaderMessage(message);
break;
case HEARTBEAT:
LOGGER.info("Instance " + localId + " - Heartbeat Message handling...");
handleHeartbeatMessage(message);
break;
case ELECTION_INVOKE:
LOGGER.info("Instance " + localId + " - Election Invoke Message handling...");
handleElectionInvokeMessage();
break;
case LEADER_INVOKE:
LOGGER.info("Instance " + localId + " - Leader Invoke Message handling...");
handleLeaderInvokeMessage();
break;
case HEARTBEAT_INVOKE:
LOGGER.info("Instance " + localId + " - Heartbeat Invoke Message handling...");
handleHeartbeatInvokeMessage();
break;
default:
break;
}
}
/**
* Abstract methods to handle different types of message. These methods need to be implemented in concrete instance
* class to implement corresponding leader-selection pattern.
*/
protected abstract void handleElectionMessage(Message message);
protected abstract void handleElectionInvokeMessage();
protected abstract void handleLeaderMessage(Message message);
protected abstract void handleLeaderInvokeMessage();
protected abstract void handleHeartbeatMessage(Message message);
protected abstract void handleHeartbeatInvokeMessage();
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/**
* Abstract class of all the message manager classes.
*/
public abstract class AbstractMessageManager implements MessageManager {
/**
* Contain all the instances in the system. Key is its ID, and value is the instance itself.
*/
protected Map<Integer, Instance> instanceMap;
/**
* Construtor of AbstractMessageManager
*/
public AbstractMessageManager(Map<Integer, Instance> instanceMap) {
this.instanceMap = instanceMap;
}
/**
* Find the next instance with smallest ID.
* @return The next instance.
*/
protected Instance findNextInstance(int currentId) {
Instance result = null;
List<Integer> candidateList = instanceMap.keySet()
.stream()
.filter((i) -> i > currentId && instanceMap.get(i).isAlive())
.sorted()
.collect(Collectors.toList());
if (candidateList.isEmpty()) {
int index = instanceMap.keySet()
.stream()
.filter((i) -> instanceMap.get(i).isAlive())
.sorted()
.collect(Collectors.toList())
.get(0);
result = instanceMap.get(index);
} else {
int index = candidateList.get(0);
result = instanceMap.get(index);
}
return result;
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
/**
* Instance interface
*/
public interface Instance {
/**
* Check if the instance is alive or not.
* @return {@code true} if the instance is alive.
*/
boolean isAlive();
/**
* Set the health status of the certain instance.
* @param alive {@code true} for alive.
*/
void setAlive(boolean alive);
/**
* Consume messages from other instances.
* @param message Message sent by other instances
*/
void onMessage(Message message);
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
import java.util.Objects;
/**
* Message used to transport data between instances.
*/
public class Message {
private MessageType type;
private String content;
public Message() {}
public Message(MessageType type, String content) {
this.type = type;
this.content = content;
}
public MessageType getType() {
return type;
}
public void setType(MessageType type) {
this.type = type;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Message message = (Message) o;
return type == message.type && Objects.equals(content, message.content);
}
@Override
public int hashCode() {
return Objects.hash(type, content);
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
/**
* MessageManager interface
*/
public interface MessageManager {
/**
* Send heartbeat message to leader instance to check whether the leader instance is alive.
* @param leaderId Instance ID of leader instance.
* @return {@code true} if leader instance is alive, or {@code false} if not.
*/
boolean sendHeartbeatMessage(int leaderId);
/**
* Send election message to other instances.
* @param currentId Instance ID of which sends this message.
* @param content Election message content.
* @return {@code true} if the message is accepted by the target instances.
*/
boolean sendElectionMessage(int currentId, String content);
/**
* Send new leader notification message to other instances.
* @param currentId Instance ID of which sends this message.
* @param leaderId Leader message content.
* @return {@code true} if the message is accepted by the target instances.
*/
boolean sendLeaderMessage(int currentId, int leaderId);
/**
* Send heartbeat invoke message. This will invoke heartbeat task in the target instance.
* @param currentId Instance ID of which sends this message.
*/
void sendHeartbeatInvokeMessage(int currentId);
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
/**
* Message Type enum
*/
public enum MessageType {
/**
* Start the election. The content of the message stores ID(s) of the candidate instance(s).
*/
ELECTION,
/**
* Nodify the new leader. The content of the message should be the leader ID.
*/
LEADER,
/**
* Check health of current leader instance.
*/
HEARTBEAT,
/**
* Inform target instance to start election.
*/
ELECTION_INVOKE,
/**
* Inform target instance to notify all the other instance that it is the new leader.
*/
LEADER_INVOKE,
/**
* Inform target instance to start heartbeat.
*/
HEARTBEAT_INVOKE
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import com.iluwatar.leaderelection.Instance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageManager;
import com.iluwatar.leaderelection.MessageType;
import java.util.HashMap;
import java.util.Map;
/**
* Example of how to use bully leader election. Initially 5 instances is created in the clould
* system, and the instance with ID 1 is set as leader. After the system is started stop the
* leader instance, and the new leader will be elected.
*/
public class BullyApp {
/**
* Program entry point
*/
public static void main(String[] args) {
Map<Integer, Instance> instanceMap = new HashMap<>();
MessageManager messageManager = new BullyMessageManager(instanceMap);
BullyInstance instance1 = new BullyInstance(messageManager, 1, 1);
BullyInstance instance2 = new BullyInstance(messageManager, 2, 1);
BullyInstance instance3 = new BullyInstance(messageManager, 3, 1);
BullyInstance instance4 = new BullyInstance(messageManager, 4, 1);
BullyInstance instance5 = new BullyInstance(messageManager, 5, 1);
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
instanceMap.put(4, instance4);
instanceMap.put(5, instance5);
instance4.onMessage(new Message(MessageType.HEARTBEAT_INVOKE, ""));
Thread thread1 = new Thread(instance1);
Thread thread2 = new Thread(instance2);
Thread thread3 = new Thread(instance3);
Thread thread4 = new Thread(instance4);
Thread thread5 = new Thread(instance5);
thread1.start();
thread2.start();
thread3.start();
thread4.start();
thread5.start();
instance1.setAlive(false);
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import com.iluwatar.leaderelection.AbstractInstance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Impelemetation with bully algorithm. Each instance should have a sequential id and is able to
* communicate with other instances in the system. Initially the instance with smallest (or largest)
* ID is selected to be the leader. All the other instances send heartbeat message to leader periodically
* to check its health. If one certain instance finds the server done, it will send an election message
* to all the instances of which the ID is larger. If the target instance is alive, it will return an
* alive message (in this sample return true) and then send election message with its ID. If not,
* the original instance will send leader message to all the other instances.
*/
public class BullyInstance extends AbstractInstance {
private static final Logger LOGGER = LoggerFactory.getLogger(BullyInstance.class);
/**
* Constructor of BullyInstance.
*/
public BullyInstance(MessageManager messageManager, int localId, int leaderId) {
super(messageManager, localId, leaderId);
}
/**
* Process the heartbeat invoke message. After receiving the message, the instance will send a heartbeat
* to leader to check its health. If alive, it will inform the next instance to do the heartbeat. If not,
* it will start the election process.
*/
@Override
protected void handleHeartbeatInvokeMessage() {
try {
boolean isLeaderAlive = messageManager.sendHeartbeatMessage(leaderId);
if (isLeaderAlive) {
LOGGER.info("Instance " + localId + "- Leader is alive.");
Thread.sleep(HEARTBEAT_INTERVAL);
messageManager.sendHeartbeatInvokeMessage(localId);
} else {
LOGGER.info("Instance " + localId + "- Leader is not alive. Start election.");
boolean electionResult = messageManager.sendElectionMessage(localId, String.valueOf(localId));
if (electionResult) {
LOGGER.info("Instance " + localId + "- Succeed in election. Start leader notification.");
messageManager.sendLeaderMessage(localId, localId);
}
}
} catch (InterruptedException e) {
LOGGER.info("Instance " + localId + "- Interrupted.");
}
}
/**
* Process election invoke message. Send election message to all the instances with smaller ID. If any
* one of them is alive, do nothing. If no instance alive, send leader message to all the alive instance
* and restart heartbeat.
*/
@Override
protected void handleElectionInvokeMessage() {
if (!isLeader()) {
LOGGER.info("Instance " + localId + "- Start election.");
boolean electionResult = messageManager.sendElectionMessage(localId, String.valueOf(localId));
if (electionResult) {
LOGGER.info("Instance " + localId + "- Succeed in election. Start leader notification.");
leaderId = localId;
messageManager.sendLeaderMessage(localId, localId);
messageManager.sendHeartbeatInvokeMessage(localId);
}
}
}
/**
* Process leader message. Update local leader information.
*/
@Override
protected void handleLeaderMessage(Message message) {
leaderId = Integer.valueOf(message.getContent());
LOGGER.info("Instance " + localId + " - Leader update done.");
}
private boolean isLeader() {
return localId == leaderId;
}
/**
* Not used in Bully instance.
*/
@Override
protected void handleLeaderInvokeMessage() {}
@Override
protected void handleHeartbeatMessage(Message message) {}
@Override
protected void handleElectionMessage(Message message) {}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import com.iluwatar.leaderelection.AbstractMessageManager;
import com.iluwatar.leaderelection.Instance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageType;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/**
* Implementation of BullyMessageManager
*/
public class BullyMessageManager extends AbstractMessageManager {
/**
* Constructor of BullyMessageManager.
*/
public BullyMessageManager(Map<Integer, Instance> instanceMap) {
super(instanceMap);
}
/**
* Send heartbeat message to current leader instance to check the health.
* @param leaderId leaderID
* @return {@code true} if the leader is alive.
*/
@Override
public boolean sendHeartbeatMessage(int leaderId) {
Instance leaderInstance = instanceMap.get(leaderId);
boolean alive = leaderInstance.isAlive();
return alive;
}
/**
* Send election message to all the instances with smaller ID.
* @param currentId Instance ID of which sends this message.
* @param content Election message content.
* @return {@code true} if no alive instance has smaller ID, so that the election is accepted.
*/
@Override
public boolean sendElectionMessage(int currentId, String content) {
List<Integer> candidateList = findElectionCandidateInstanceList(currentId);
if (candidateList.isEmpty()) {
return true;
} else {
Message electionMessage = new Message(MessageType.ELECTION_INVOKE, "");
candidateList.stream()
.forEach((i) -> instanceMap.get(i).onMessage(electionMessage));
return false;
}
}
/**
* Send leader message to all the instances to notify the new leader.
* @param currentId Instance ID of which sends this message.
* @param leaderId Leader message content.
* @return {@code true} if the message is accepted.
*/
@Override
public boolean sendLeaderMessage(int currentId, int leaderId) {
Message leaderMessage = new Message(MessageType.LEADER, String.valueOf(leaderId));
instanceMap.keySet()
.stream()
.filter((i) -> i != currentId)
.forEach((i) -> instanceMap.get(i).onMessage(leaderMessage));
return false;
}
/**
* Send heartbeat invoke message to the next instance.
* @param currentId Instance ID of which sends this message.
*/
@Override
public void sendHeartbeatInvokeMessage(int currentId) {
Instance nextInstance = this.findNextInstance(currentId);
Message heartbeatInvokeMessage = new Message(MessageType.HEARTBEAT_INVOKE, "");
nextInstance.onMessage(heartbeatInvokeMessage);
}
/**
* Find all the alive instances with smaller ID than current instance.
* @param currentId ID of current instance.
* @return ID list of all the candidate instance.
*/
private List<Integer> findElectionCandidateInstanceList(int currentId) {
return instanceMap.keySet()
.stream()
.filter((i) -> i < currentId && instanceMap.get(i).isAlive())
.collect(Collectors.toList());
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import com.iluwatar.leaderelection.Instance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageManager;
import com.iluwatar.leaderelection.MessageType;
import java.util.HashMap;
import java.util.Map;
/**
* Example of how to use ring leader election. Initially 5 instances is created in the clould
* system, and the instance with ID 1 is set as leader. After the system is started stop the
* leader instance, and the new leader will be elected.
*/
public class RingApp {
/**
* Program entry point
*/
public static void main(String[] args) {
Map<Integer, Instance> instanceMap = new HashMap<>();
MessageManager messageManager = new RingMessageManager(instanceMap);
RingInstance instance1 = new RingInstance(messageManager, 1, 1);
RingInstance instance2 = new RingInstance(messageManager, 2, 1);
RingInstance instance3 = new RingInstance(messageManager, 3, 1);
RingInstance instance4 = new RingInstance(messageManager, 4, 1);
RingInstance instance5 = new RingInstance(messageManager, 5, 1);
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
instanceMap.put(4, instance4);
instanceMap.put(5, instance5);
instance2.onMessage(new Message(MessageType.HEARTBEAT_INVOKE, ""));
Thread thread1 = new Thread(instance1);
Thread thread2 = new Thread(instance2);
Thread thread3 = new Thread(instance3);
Thread thread4 = new Thread(instance4);
Thread thread5 = new Thread(instance5);
thread1.start();
thread2.start();
thread3.start();
thread4.start();
thread5.start();
instance1.setAlive(false);
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import com.iluwatar.leaderelection.AbstractInstance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
/**
* Implementation with token ring algorithm. The instances in the system are organized as a ring.
* Each instance should have a sequential id and the instance with smallest (or largest) id should
* be the initial leader. All the other instances send heartbeat message to leader periodically
* to check its health. If one certain instance finds the server done, it will send an election
* message to the next alive instance in the ring, which contains its own ID. Then the next instance
* add its ID into the message and pass it to the next. After all the alive instances' ID are add
* to the message, the message is send back to the first instance and it will choose the instance
* with smallest ID to be the new leader, and then send a leader message to other instances to
* inform the result.
*/
public class RingInstance extends AbstractInstance {
private static final Logger LOGGER = LoggerFactory.getLogger(RingInstance.class);
/**
* Constructor of RingInstance.
*/
public RingInstance(MessageManager messageManager, int localId, int leaderId) {
super(messageManager, localId, leaderId);
}
/**
* Process the heartbeat invoke message. After receiving the message, the instance will send a heartbeat
* to leader to check its health. If alive, it will inform the next instance to do the heartbeat. If not,
* it will start the election process.
*/
@Override
protected void handleHeartbeatInvokeMessage() {
try {
boolean isLeaderAlive = messageManager.sendHeartbeatMessage(this.leaderId);
if (isLeaderAlive) {
LOGGER.info("Instance " + localId + "- Leader is alive. Start next heartbeat in 5 second.");
Thread.sleep(HEARTBEAT_INTERVAL);
messageManager.sendHeartbeatInvokeMessage(this.localId);
} else {
LOGGER.info("Instance " + localId + "- Leader is not alive. Start election.");
messageManager.sendElectionMessage(this.localId, String.valueOf(this.localId));
}
} catch (InterruptedException e) {
LOGGER.info("Instance " + localId + "- Interrupted.");
}
}
/**
* Process election message. If the local ID is contained in the ID list, the instance will select the
* alive instance with smallest ID to be the new leader, and send the leader inform message. If not,
* it will add its local ID to the list and send the message to the next instance in the ring.
*/
@Override
protected void handleElectionMessage(Message message) {
String content = message.getContent();
LOGGER.info("Instance " + localId + " - Election Message: " + content);
List<Integer> candidateList =
Arrays.stream(content.trim().split(","))
.map(Integer::valueOf)
.sorted()
.collect(Collectors.toList());
if (candidateList.contains(localId)) {
int newLeaderId = candidateList.get(0);
LOGGER.info("Instance " + localId + " - New leader should be " + newLeaderId + ".");
messageManager.sendLeaderMessage(localId, newLeaderId);
} else {
content += "," + localId;
messageManager.sendElectionMessage(localId, content);
}
}
/**
* Process leader Message. The instance will set the leader ID to be the new one and send the message to
* the next instance until all the alive instance in the ring is informed.
*/
@Override
protected void handleLeaderMessage(Message message) {
int newLeaderId = Integer.valueOf(message.getContent());
if (this.leaderId != newLeaderId) {
LOGGER.info("Instance " + localId + " - Update leaderID");
this.leaderId = newLeaderId;
messageManager.sendLeaderMessage(localId, newLeaderId);
} else {
LOGGER.info("Instance " + localId + " - Leader update done. Start heartbeat.");
messageManager.sendHeartbeatInvokeMessage(localId);
}
}
/**
* Not used in Ring instance.
*/
@Override
protected void handleLeaderInvokeMessage() {}
@Override
protected void handleHeartbeatMessage(Message message) {}
@Override
protected void handleElectionInvokeMessage() {}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import com.iluwatar.leaderelection.AbstractMessageManager;
import com.iluwatar.leaderelection.Instance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageType;
import java.util.Map;
/**
* Implementation of RingMessageManager
*/
public class RingMessageManager extends AbstractMessageManager {
/**
* Constructor of RingMessageManager.
*/
public RingMessageManager(Map<Integer, Instance> instanceMap) {
super(instanceMap);
}
/**
* Send heartbeat message to current leader instance to check the health.
* @param leaderId leaderID
* @return {@code true} if the leader is alive.
*/
@Override
public boolean sendHeartbeatMessage(int leaderId) {
Instance leaderInstance = instanceMap.get(leaderId);
boolean alive = leaderInstance.isAlive();
return alive;
}
/**
* Send election message to the next instance.
* @param currentId currentID
* @param content list contains all the IDs of instances which have received this election message.
* @return {@code true} if the election message is accepted by the target instance.
*/
@Override
public boolean sendElectionMessage(int currentId, String content) {
Instance nextInstance = this.findNextInstance(currentId);
Message electionMessage = new Message(MessageType.ELECTION, content);
nextInstance.onMessage(electionMessage);
return true;
}
/**
* Send leader message to the next instance.
* @param currentId Instance ID of which sends this message.
* @param leaderId Leader message content.
* @return {@code true} if the leader message is accepted by the target instance.
*/
@Override
public boolean sendLeaderMessage(int currentId, int leaderId) {
Instance nextInstance = this.findNextInstance(currentId);
Message leaderMessage = new Message(MessageType.LEADER, String.valueOf(leaderId));
nextInstance.onMessage(leaderMessage);
return true;
}
/**
* Send heartbeat invoke message to the next instance.
* @param currentId Instance ID of which sends this message.
*/
@Override
public void sendHeartbeatInvokeMessage(int currentId) {
Instance nextInstance = this.findNextInstance(currentId);
Message heartbeatInvokeMessage = new Message(MessageType.HEARTBEAT_INVOKE, "");
nextInstance.onMessage(heartbeatInvokeMessage);
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;
/**
* Message test case.
*/
public class MessageTest {
@Test
public void testGetType() {
Message message = new Message(MessageType.HEARTBEAT, "");
assertEquals(MessageType.HEARTBEAT, message.getType());
}
@Test
public void testGetContent() {
String content = "test";
Message message = new Message(MessageType.HEARTBEAT, content);
assertEquals(content, message.getContent());
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import org.junit.jupiter.api.Test;
/**
* BullyApp unit test.
*/
public class BullyAppTest {
@Test
public void test() {
String[] args = {};
BullyApp.main(args);
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import com.iluwatar.leaderelection.*;
import com.iluwatar.leaderelection.ring.RingInstance;
import com.iluwatar.leaderelection.ring.RingMessageManager;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
import java.util.Queue;
import static org.junit.jupiter.api.Assertions.*;
/**
* BullyMessageManager unit test.
*/
public class BullyMessageManagerTest {
@Test
public void testSendHeartbeatMessage() {
Instance instance1 = new BullyInstance(null, 1, 1);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
MessageManager messageManager = new BullyMessageManager(instanceMap);
assertTrue(messageManager.sendHeartbeatMessage(1));
}
@Test
public void testSendElectionMessageNotAccepted() {
try {
Instance instance1 = new BullyInstance(null, 1, 1);
Instance instance2 = new BullyInstance(null, 1, 2);
Instance instance3 = new BullyInstance(null, 1, 3);
Instance instance4 = new BullyInstance(null, 1, 4);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
instanceMap.put(4, instance4);
instance1.setAlive(false);
MessageManager messageManager = new BullyMessageManager(instanceMap);
boolean result = messageManager.sendElectionMessage(3, "3");
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message message2 = ((Queue<Message>) messageQueueField.get(instance2)).poll();
int instance4QueueSize = ((Queue<Message>) messageQueueField.get(instance4)).size();
Message expectedMessage = new Message(MessageType.ELECTION_INVOKE, "");
assertEquals(message2, expectedMessage);
assertEquals(instance4QueueSize, 0);
assertEquals(result, false);
} catch (IllegalAccessException | NoSuchFieldException e) {
fail("Error to access private field.");
}
}
@Test
public void testElectionMessageAccepted() {
Instance instance1 = new BullyInstance(null, 1, 1);
Instance instance2 = new BullyInstance(null, 1, 2);
Instance instance3 = new BullyInstance(null, 1, 3);
Instance instance4 = new BullyInstance(null, 1, 4);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
instanceMap.put(4, instance4);
instance1.setAlive(false);
MessageManager messageManager = new BullyMessageManager(instanceMap);
boolean result = messageManager.sendElectionMessage(2, "2");
assertEquals(result, true);
}
@Test
public void testSendLeaderMessage() {
try {
Instance instance1 = new BullyInstance(null, 1, 1);
Instance instance2 = new BullyInstance(null, 1, 2);
Instance instance3 = new BullyInstance(null, 1, 3);
Instance instance4 = new BullyInstance(null, 1, 4);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
instanceMap.put(4, instance4);
instance1.setAlive(false);
MessageManager messageManager = new BullyMessageManager(instanceMap);
messageManager.sendLeaderMessage(2, 2);
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message message3 = ((Queue<Message>) messageQueueField.get(instance3)).poll();
Message message4 = ((Queue<Message>) messageQueueField.get(instance4)).poll();
Message expectedMessage = new Message(MessageType.LEADER, "2");
assertEquals(message3, expectedMessage);
assertEquals(message4, expectedMessage);
} catch (IllegalAccessException | NoSuchFieldException e) {
fail("Error to access private field.");
}
}
@Test
public void testSendHeartbeatInvokeMessage() {
try {
Instance instance1 = new BullyInstance(null, 1, 1);
Instance instance2 = new BullyInstance(null, 1, 2);
Instance instance3 = new BullyInstance(null, 1, 3);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
MessageManager messageManager = new BullyMessageManager(instanceMap);
messageManager.sendHeartbeatInvokeMessage(2);
Message message = new Message(MessageType.HEARTBEAT_INVOKE, "");
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message messageSent = ((Queue<Message>) messageQueueField.get(instance3)).poll();
assertEquals(messageSent.getType(), message.getType());
assertEquals(messageSent.getContent(), message.getContent());
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Error to access private field.");
}
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.bully;
import com.iluwatar.leaderelection.AbstractInstance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageType;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Field;
import java.util.Queue;
import static org.junit.jupiter.api.Assertions.*;
/**
* BullyInstance unit test.
*/
public class BullyinstanceTest {
@Test
public void testOnMessage() {
try {
final BullyInstance bullyInstance = new BullyInstance(null, 1, 1);
Message bullyMessage = new Message(MessageType.HEARTBEAT, "");
bullyInstance.onMessage(bullyMessage);
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
assertEquals(bullyMessage, ((Queue<Message>) messageQueueField.get(bullyInstance)).poll());
} catch (IllegalAccessException | NoSuchFieldException e) {
fail("fail to access messasge queue.");
}
}
@Test
public void testIsAlive() {
try {
final BullyInstance bullyInstance = new BullyInstance(null, 1, 1);
Class instanceClass = AbstractInstance.class;
Field aliveField = instanceClass.getDeclaredField("alive");
aliveField.setAccessible(true);
aliveField.set(bullyInstance, false);
assertFalse(bullyInstance.isAlive());
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Fail to access field alive.");
}
}
@Test
public void testSetAlive() {
final BullyInstance bullyInstance = new BullyInstance(null, 1, 1);
bullyInstance.setAlive(false);
assertFalse(bullyInstance.isAlive());
}
}

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/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import org.junit.jupiter.api.Test;
/**
* RingApp unit test.
*/
public class RingAppTest {
@Test
public void test() {
String[] args = {};
RingApp.main(args);
}
}

76
leader-election/src/test/java/com/iluwatar/leaderelection/ring/RingInstanceTest.java Normal file
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@ -0,0 +1,76 @@
/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import com.iluwatar.leaderelection.AbstractInstance;
import com.iluwatar.leaderelection.Message;
import com.iluwatar.leaderelection.MessageType;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Field;
import java.util.Queue;
import static org.junit.jupiter.api.Assertions.*;
/**
* RingInstance unit test.
*/
public class RingInstanceTest {
@Test
public void testOnMessage() {
try {
final RingInstance ringInstance = new RingInstance(null, 1, 1);
Message ringMessage = new Message(MessageType.HEARTBEAT, "");
ringInstance.onMessage(ringMessage);
Class ringInstanceClass = AbstractInstance.class;
Field messageQueueField = ringInstanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
assertEquals(ringMessage, ((Queue<Message>) messageQueueField.get(ringInstance)).poll());
} catch (IllegalAccessException | NoSuchFieldException e) {
fail("fail to access messasge queue.");
}
}
@Test
public void testIsAlive() {
try {
final RingInstance ringInstance = new RingInstance(null, 1, 1);
Class ringInstanceClass = AbstractInstance.class;
Field aliveField = ringInstanceClass.getDeclaredField("alive");
aliveField.setAccessible(true);
aliveField.set(ringInstance, false);
assertFalse(ringInstance.isAlive());
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Fail to access field alive.");
}
}
@Test
public void testSetAlive() {
final RingInstance ringInstance = new RingInstance(null, 1, 1);
ringInstance.setAlive(false);
assertFalse(ringInstance.isAlive());
}
}

123
leader-election/src/test/java/com/iluwatar/leaderelection/ring/RingMessageManagerTest.java Normal file
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@ -0,0 +1,123 @@
/**
* The MIT License
* Copyright (c) 2014-2016 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.leaderelection.ring;
import com.iluwatar.leaderelection.*;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
import java.util.Queue;
import static org.junit.jupiter.api.Assertions.*;
/**
* RingMessageManager unit test.
*/
public class RingMessageManagerTest {
@Test
public void testSendHeartbeatMessage() {
Instance instance1 = new RingInstance(null, 1, 1);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
MessageManager messageManager = new RingMessageManager(instanceMap);
assertTrue(messageManager.sendHeartbeatMessage(1));
}
@Test
public void testSendElectionMessage() {
try {
Instance instance1 = new RingInstance(null, 1, 1);
Instance instance2 = new RingInstance(null, 1, 2);
Instance instance3 = new RingInstance(null, 1, 3);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
MessageManager messageManager = new RingMessageManager(instanceMap);
String messageContent = "2";
messageManager.sendElectionMessage(2, messageContent);
Message ringMessage = new Message(MessageType.ELECTION, messageContent);
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message ringMessageSent = ((Queue<Message>) messageQueueField.get(instance3)).poll();
assertEquals(ringMessageSent.getType(), ringMessage.getType());
assertEquals(ringMessageSent.getContent(), ringMessage.getContent());
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Error to access private field.");
}
}
@Test
public void testSendLeaderMessage() {
try {
Instance instance1 = new RingInstance(null, 1, 1);
Instance instance2 = new RingInstance(null, 1, 2);
Instance instance3 = new RingInstance(null, 1, 3);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
MessageManager messageManager = new RingMessageManager(instanceMap);
String messageContent = "3";
messageManager.sendLeaderMessage(2, 3);
Message ringMessage = new Message(MessageType.LEADER, messageContent);
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message ringMessageSent = ((Queue<Message>) messageQueueField.get(instance3)).poll();
assertEquals(ringMessageSent, ringMessage);
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Error to access private field.");
}
}
@Test
public void testSendHeartbeatInvokeMessage() {
try {
Instance instance1 = new RingInstance(null, 1, 1);
Instance instance2 = new RingInstance(null, 1, 2);
Instance instance3 = new RingInstance(null, 1, 3);
Map<Integer, Instance> instanceMap = new HashMap<>();
instanceMap.put(1, instance1);
instanceMap.put(2, instance2);
instanceMap.put(3, instance3);
MessageManager messageManager = new RingMessageManager(instanceMap);
messageManager.sendHeartbeatInvokeMessage(2);
Message ringMessage = new Message(MessageType.HEARTBEAT_INVOKE, "");
Class instanceClass = AbstractInstance.class;
Field messageQueueField = instanceClass.getDeclaredField("messageQueue");
messageQueueField.setAccessible(true);
Message ringMessageSent = ((Queue<Message>) messageQueueField.get(instance3)).poll();
assertEquals(ringMessageSent.getType(), ringMessage.getType());
assertEquals(ringMessageSent.getContent(), ringMessage.getContent());
} catch (NoSuchFieldException | IllegalAccessException e) {
fail("Error to access private field.");
}
}
}

2
pom.xml
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@ -176,7 +176,9 @@
<module>commander</module>
<module>typeobjectpattern</module>
<module>bytecode</module>
<module>leader-election</module>
<module>data-locality</module>
</modules>
<repositories>