Fix Bug

Readme.md

@@ -11,8 +11,7 @@ This project demonstrates a simple implementation of distributed locking using A
 - [Usage](#usage)
 - [Dependencies](#dependencies)
 - [Running the Project](#running-the-project)
-- [Contributing](#contributing)
-- [License](#license)
+
 
 ## Overview
 
@@ -76,9 +75,9 @@ To use this distributed locking mechanism in your project, follow these steps:
    mvn clean install
    ```
 
-3. **Run the Application**:
+3. **Run the Application three times to simulate three services trying to get the lock**:
    ```bash
-   java -cp target/DLock-1.0-SNAPSHOT.jar org.ds.Locks
+   java -cp target/DLock-1.0-SNAPSHOT.jar org.ds.Locks 
    ```
 
 ## Dependencies

src/main/java/org/ds/Locks.java

@@ -2,7 +2,6 @@ package org.ds;
 
 
 import org.apache.zookeeper.*;
-import org.apache.zookeeper.data.Stat;
 
 import java.io.IOException;
 import java.util.Collections;
@@ -11,8 +10,8 @@ import java.util.List;
 public class Locks implements Watcher {
 
     private static final String ADDRESS = "172.29.3.101:2181";
-    private static final int SESSION_TIMEOUT = 3000;
-    private static final String LOCKS = "/locks";
+    private static final int SESSION_TIMEOUT = 30000;
+    private static final String LOCKS = "/locksM";
     private String myCandidate;
     private ZooKeeper zooKeeper;
 
@@ -21,42 +20,43 @@ public class Locks implements Watcher {
         Locks locks = new Locks();
         locks.connectToZookeeper();
 
-        locks.CheckLock();
+        locks.initLock();
         locks.getLockOrWait();
 
         locks.run();
         locks.close();
     }
 
-    private void CheckLock() throws KeeperException, InterruptedException {
+    private void initLock() throws KeeperException, InterruptedException {
         if (zooKeeper.exists(LOCKS, false) == null) {
             zooKeeper.create(LOCKS, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
         }
         String path = zooKeeper.create(LOCKS + "/" + "lock-", new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
         myCandidate = path.replace(LOCKS + "/", "");
+        System.out.println("myCandidate " + myCandidate);
     }
 
     private void getLockOrWait() throws KeeperException, InterruptedException {
-        CheckLock();
 
-        Stat stat = null;
         String predecessor = "";
-        while (stat == null) {
-            List<String> children = zooKeeper.getChildren(LOCKS, false);
-//        System.out.println(children);
-            Collections.sort(children);
-            if (children.get(0).equals(myCandidate)) {
-                System.out.println("I acquired a lock :). will leave it in 10 seconds");
-                for (int i = 0; i < 10; i++) {
-                    System.out.println("leaving in " + i + "seconds");
-                    Thread.sleep(1000);
-                }
-                zooKeeper.delete(LOCKS + "/" + children.get(0), -1);
-            } else {
-                System.out.println("i could not acquire a lock. So will wait");
-                int predecessorIndex = Collections.binarySearch(children, myCandidate) - 1;
-                predecessor = children.get(predecessorIndex);
-                    stat = zooKeeper.exists(LOCKS + "/" + predecessor, this);
+        List<String> children = zooKeeper.getChildren(LOCKS, false);
+        System.out.println("List of children " + children);
+        Collections.sort(children);
+        if (children.get(0).equals(myCandidate)) {
+            System.out.println("I acquired a lock :). will leave it in 10 seconds");
+            for (int i = 0; i < 10; i++) {
+                System.out.println("leaving in " + (10 - i) + "seconds");
+                Thread.sleep(1000);
+            }
+            zooKeeper.delete(LOCKS + "/" + myCandidate, -1);
+        } else {
+            System.out.println("i could not acquire a lock. So will wait");
+            int predecessorIndex = Collections.binarySearch(children, myCandidate) - 1;
+            predecessor = children.get(predecessorIndex);
+
+            //Check Race Condition
+            if (zooKeeper.exists(LOCKS + "/" + predecessor, this) == null) {
+                getLockOrWait();
             }
         }
     }
@@ -78,7 +78,7 @@ public class Locks implements Watcher {
 
     @Override
     public void process(WatchedEvent watchedEvent) {
-        if (watchedEvent.getType() == Event.EventType.NodeChildrenChanged) {
+        if (watchedEvent.getType() == Event.EventType.NodeDeleted) {
             try {
                 getLockOrWait();
             } catch (KeeperException e) {