Lock Objects and AtomicVariables examples

Author: Rajeev Kumar Singh

.gitignore

@@ -2,3 +2,4 @@
 .idea
 out
 *.iml
+*.class

java-lock-objects-and-atomic-variables/src/ReadWriteLockExample.java

@@ -1,5 +1,60 @@
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
 /**
  * Created by rajeevkumarsingh on 11/05/17.
  */
+class ReadWriteCounter {
+    ReadWriteLock lock = new ReentrantReadWriteLock();
+
+    private int count = 0;
+
+    public int incrementAndGetCount() {
+        lock.writeLock().lock();
+
+        try {
+            count = count + 1;
+            return count;
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
+    public int getCount() {
+        lock.readLock().lock();
+        try {
+            return count;
+        } finally {
+            lock.readLock().unlock();
+        }
+    }
+}
+
 public class ReadWriteLockExample {
+
+    public static void main(String[] args) {
+        ExecutorService executorService = Executors.newFixedThreadPool(3);
+
+        ReadWriteCounter counter = new ReadWriteCounter();
+
+        Runnable readTask = () -> {
+          System.out.println(Thread.currentThread().getName() +
+                  " Read Task : " + counter.getCount());
+        };
+
+        Runnable writeTask = () -> {
+            System.out.println(Thread.currentThread().getName() +
+                    " Write Task : " + counter.incrementAndGetCount());
+        };
+
+        executorService.submit(readTask);
+        executorService.submit(readTask);
+
+        executorService.submit(writeTask);
+
+        executorService.submit(readTask);
+        executorService.submit(readTask);
+    }
 }

java-lock-objects-and-atomic-variables/src/ReentrantLockExample.java

@@ -11,6 +11,7 @@ class ReentrantLockCounter {
 
     private int count = 0;
 
+    // Thread Safe Increment
     public void increment() {
         lock.lock();
         try {
@@ -30,11 +31,13 @@ public int getCount() {
 public class ReentrantLockExample {
 
     public static void main(String[] args) throws InterruptedException {
-        ExecutorService executorService = Executors.newFixedThreadPool(2);
+        ExecutorService executorService = Executors.newFixedThreadPool(5);
 
         ReentrantLockCounter counter = new ReentrantLockCounter();
 
-        for(int i = 0; i < 1000; i++) {
+        executorService.submit(() -> counter.increment());
+
+        for(int i = 0; i < 10; i++) {
             executorService.submit(() -> counter.increment());
         }
 

java-lock-objects-and-atomic-variables/src/StampedLockExample.java

@@ -10,7 +10,7 @@ public static void main(String[] args) {
             try {
                 Thread.sleep(2000);
             } catch (InterruptedException e) {
-                e.printStackTrace();
+                throw new IllegalStateException(e);
             }
             System.out.println("Exiting Thread 1");
         });
@@ -21,7 +21,7 @@ public static void main(String[] args) {
             try {
                 Thread.sleep(4000);
             } catch (InterruptedException e) {
-                e.printStackTrace();
+                throw new IllegalStateException(e);
             }
             System.out.println("Exiting Thread 2");
         });
@@ -33,7 +33,7 @@ public static void main(String[] args) {
         try {
             thread1.join(1000);
         } catch (InterruptedException e) {
-            e.printStackTrace();
+            throw new IllegalStateException(e);
         }
 
         System.out.println("Waited enough! Starting Thread 2 now");

java-thread-and-runnable-examples/src/RunnableExample.class

@@ -22,7 +22,7 @@ public static void main(String[] args) {
                 try {
                     Thread.sleep(2000);
                 } catch (InterruptedException e) {
-                    e.printStackTrace();
+                    throw new IllegalStateException(e);
                 }
             }
         };