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
2026-05-17 14:59:37 +00:00 · 2019-10-08 23:29:59 +08:00
parent 41b8d80479
commit 90ea4506ca
22 changed files with 1719 additions and 0 deletions
@@ -0,0 +1,148 @@
+/**
+ * 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();
+
+}