feature: resolve #1282 for Lockable Object pattern. (#1702)

* Added Lockable-Object pattern. Closes #1282. * Refactor method name. * Refactor sonar lint bugs. * Added tests and enum Constants. * Increase coverage. * Changed @Data to Getters and Setters. * Iluwatar's comment on pull request #1702. * Fixed codes mells. * Incremented wait time to 3 seconds. * Reduced wait time to 2 seconds. * Cleaned Code Smells. * Incremented wait time, removed cool down. * Refactored README.md file. Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>
2026-05-14 18:58:44 +00:00 · 2021-05-14 18:56:41 +03:00
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+package com.iluwatar.lockableobject;
+
+import com.iluwatar.lockableobject.domain.Creature;
+import com.iluwatar.lockableobject.domain.Elf;
+import com.iluwatar.lockableobject.domain.Feind;
+import com.iluwatar.lockableobject.domain.Human;
+import com.iluwatar.lockableobject.domain.Orc;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * The Lockable Object pattern is a concurrency pattern. Instead of using the "synchronized" word
+ * upon the methods to be synchronized, the object which implements the Lockable interface handles
+ * the request.
+ *
+ * <p>In this example, we create a new Lockable object with the SwordOfAragorn implementation of it.
+ * Afterwards we create 6 Creatures with the Elf, Orc and Human implementations and assign them each
+ * to a Fiend object and the Sword is the target object. Because there is only one Sword and it uses
+ * the Lockable Object pattern, only one creature can hold the sword at a given time. When the sword
+ * is locked, any other alive Fiends will try to lock, which will result in a race to lock the
+ * sword.
+ *
+ * @author Noam Greenshtain
+ */
+@Slf4j
+public class App implements Runnable {
+
+  private static final int WAIT_TIME = 3;
+  private static final int WORKERS = 2;
+  private static final int MULTIPLICATION_FACTOR = 3;
+
+  /**
+   * main method.
+   *
+   * @param args as arguments for the main method.
+   */
+  public static void main(String[] args) {
+    var app = new App();
+    app.run();
+  }
+
+  @Override
+  public void run() {
+    // The target object for this example.
+    var sword = new SwordOfAragorn();
+    // Creation of creatures.
+    List<Creature> creatures = new ArrayList<>();
+    for (var i = 0; i < WORKERS; i++) {
+      creatures.add(new Elf(String.format("Elf %s", i)));
+      creatures.add(new Orc(String.format("Orc %s", i)));
+      creatures.add(new Human(String.format("Human %s", i)));
+    }
+    int totalFiends = WORKERS * MULTIPLICATION_FACTOR;
+    ExecutorService service = Executors.newFixedThreadPool(totalFiends);
+    // Attach every creature and the sword is a Fiend to fight for the sword.
+    for (var i = 0; i < totalFiends; i = i + MULTIPLICATION_FACTOR) {
+      service.submit(new Feind(creatures.get(i), sword));
+      service.submit(new Feind(creatures.get(i + 1), sword));
+      service.submit(new Feind(creatures.get(i + 2), sword));
+    }
+    // Wait for program to terminate.
+    try {
+      if (!service.awaitTermination(WAIT_TIME, TimeUnit.SECONDS)) {
+        LOGGER.info("The master of the sword is now {}.", sword.getLocker().getName());
+      }
+    } catch (InterruptedException e) {
+      LOGGER.error(e.getMessage());
+      Thread.currentThread().interrupt();
+    } finally {
+      service.shutdown();
+    }
+  }
+}