new files

Task/Checkpoint-synchronization/Java/checkpoint-synchronization-2.java

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+import java.util.Random;
+import java.util.concurrent.CountDownLatch;
+
+public class Sync {
+	static class Worker implements Runnable {
+		private final CountDownLatch doneSignal;
+		private int threadID;
+
+		public Worker(int id, CountDownLatch doneSignal) {
+			this.doneSignal = doneSignal;
+			threadID = id;
+		}
+
+		public void run() {
+			doWork();
+			doneSignal.countDown();
+		}
+
+		void doWork() {
+			try {
+				int workTime = new Random().nextInt(900) + 100;
+				System.out.println("Worker " + threadID + " will work for " + workTime + " msec.");
+				Thread.sleep(workTime); //work for 'workTime'
+				System.out.println("Worker " + threadID + " is ready");
+			} catch (InterruptedException e) {
+				System.err.println("Error: thread execution interrupted");
+				e.printStackTrace();
+			}
+		}
+	}
+
+	public static void main(String[] args) {
+		int n = 3;//6 workers and 3 tasks
+		for(int task = 1; task <= n; task++) {
+			CountDownLatch latch = new CountDownLatch(n * 2);
+			System.out.println("Starting task " + task);
+			for(int worker = 0; worker < n * 2; worker++) {
+				new Thread(new Worker(worker, latch)).start();
+			}
+			try {
+				latch.await();//wait for n*2 threads to signal the latch
+			} catch (InterruptedException e) {
+				e.printStackTrace();
+			}
+			System.out.println("Task " + task + " complete");
+		}
+	}
+}