new tasks

Task/Checkpoint_synchronization/Java/checkpoint_synchronization-2.java

@@ -0,0 +1,48 @@
+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");
+		}
+	}
+}

Task/Checkpoint_synchronization/Java/checkpoint_synchronization.java

@@ -0,0 +1,89 @@
+import java.util.Scanner;
+import java.util.Random;
+
+public class CheckpointSync{
+	public static void main(String[] args){
+		System.out.print("Enter number of workers to use: ");
+		Scanner in = new Scanner(System.in);
+		Worker.nWorkers = in.nextInt();
+		System.out.print("Enter number of tasks to complete:");
+		runTasks(in.nextInt());
+	}
+	
+	/*
+	 * Informs that workers started working on the task and
+	 * starts running threads. Prior to proceeding with next
+	 * task syncs using static Worker.checkpoint() method.
+	 */
+	private static void runTasks(int nTasks){
+		for(int i = 0; i < nTasks; i++){
+			System.out.println("Starting task number " + (i+1) + ".");
+			runThreads();
+			Worker.checkpoint();
+		}
+	}
+	
+	/*
+	 * Creates a thread for each worker and runs it.
+	 */
+	private static void runThreads(){
+		for(int i = 0; i < Worker.nWorkers; i ++){
+			new Thread(new Worker(i+1)).start();
+		}
+	}
+	
+	/*
+	 * Worker inner static class.
+	 */
+	public static class Worker implements Runnable{
+		public Worker(int threadID){
+			this.threadID = threadID;
+		}
+		public void run(){
+			work();
+		}
+		
+		/*
+		 *  Notifies that thread started running for 100 to 1000 msec.
+		 *  Once finished increments static counter 'nFinished'
+		 *  that counts number of workers finished their work.
+		 */
+		private synchronized void work(){
+			try {
+				int workTime = rgen.nextInt(900) + 100;
+				System.out.println("Worker " + threadID + " will work for " + workTime + " msec.");
+				Thread.sleep(workTime); //work for 'workTime'
+				nFinished++; //increases work finished counter
+				System.out.println("Worker " + threadID + " is ready");
+			} catch (InterruptedException e) {
+				System.err.println("Error: thread execution interrupted");
+				e.printStackTrace();
+			}
+		}
+		
+		/*
+		 * Used to synchronize Worker threads using 'nFinished' static integer.
+		 * Waits (with step of 10 msec) until 'nFinished' equals to 'nWorkers'.
+		 * Once they are equal resets 'nFinished' counter.
+		 */
+		public static synchronized void checkpoint(){
+			while(nFinished != nWorkers){
+				try {
+					Thread.sleep(10);
+				} catch (InterruptedException e) {
+					System.err.println("Error: thread execution interrupted");
+					e.printStackTrace();
+				}
+			}
+			nFinished = 0;
+		}
+	
+		/* inner class instance variables */
+		private int threadID;
+		
+		/* static variables */
+		private static Random rgen = new Random();
+		private static int nFinished = 0;
+		public static int nWorkers = 0;
+	}
+}