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
2026-05-16 08:58:49 +00:00 · 2019-10-08 23:29:59 +08:00
parent 41b8d80479
commit 90ea4506ca
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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());
+  }
+
+}