Add code example for Semaphore

Author: abhinav-nath

src/com/codecafe/concurrency/semaphore/TaskLimitSemaphore.java

@@ -0,0 +1,85 @@
+package com.codecafe.concurrency.semaphore;
+
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.concurrent.*;
+
+// Throttle task submission
+public class TaskLimitSemaphore {
+
+  private final ExecutorService executor;
+  private final Semaphore semaphore;
+
+  public TaskLimitSemaphore(ExecutorService executor, int limit) {
+    this.executor = executor;
+    this.semaphore = new Semaphore(limit);
+  }
+
+  public <T> Future<T> submit(final Callable<T> task) throws InterruptedException {
+
+    semaphore.acquire();
+    System.out.println("semaphore.acquire()...");
+
+    return executor.submit(() -> {
+      try {
+        return task.call();
+      } finally {
+        semaphore.release();
+        System.out.println("semaphore.release()...");
+      }
+    });
+
+  }
+
+  private static final DateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
+
+  public static void main(String[] args) throws InterruptedException {
+
+    ExecutorService executor = Executors.newCachedThreadPool();
+
+    // only support 2 tasks
+    TaskLimitSemaphore obj = new TaskLimitSemaphore(executor, 2);
+
+    obj.submit(() -> {
+      System.out.println(getCurrentDateTime() + " : task1 is running!");
+      Thread.sleep(2000);
+      System.out.println(getCurrentDateTime() + " : task1 is done!");
+      return 1;
+    });
+
+    obj.submit(() -> {
+      System.out.println(getCurrentDateTime() + " : task2 is running!");
+      Thread.sleep(2000);
+      System.out.println(getCurrentDateTime() + " task2 is done!");
+      return 2;
+    });
+
+    obj.submit(() -> {
+      System.out.println(getCurrentDateTime() + " task3 is running!");
+      Thread.sleep(2000);
+      System.out.println(getCurrentDateTime() + " task3 is done!");
+      return 3;
+    });
+
+    obj.submit(() -> {
+      System.out.println(getCurrentDateTime() + " task4 is running!");
+      Thread.sleep(2000);
+      System.out.println(getCurrentDateTime() + " task4 is done!");
+      return 4;
+    });
+
+    obj.submit(() -> {
+      System.out.println(getCurrentDateTime() + " task5 is running!");
+      Thread.sleep(2000);
+      System.out.println(getCurrentDateTime() + " task5 is done!");
+      return 5;
+    });
+
+    executor.shutdown();
+  }
+
+  private static String getCurrentDateTime() {
+    return sdf.format(new Date());
+  }
+}