2 threads start at the same time (#10972)

* 2 threads start at the same time

* remove blank leading/trailing lines

core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/threadsstartatsametime/ThreadsStartAtSameTime.java

@@ -0,0 +1,59 @@
+package com.baeldung.threadsstartatsametime;
+
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.CyclicBarrier;
+
+public class ThreadsStartAtSameTime {
+
+    public static void main(String[] args) throws BrokenBarrierException, InterruptedException {
+        usingCountDownLatch();
+
+        Thread.sleep(30);
+
+        usingCyclicBarrier();
+    }
+
+    private static void usingCountDownLatch() throws InterruptedException {
+        System.out.println("===============================================");
+        System.out.println("        >>> Using CountDownLatch <<<<");
+        System.out.println("===============================================");
+
+        CountDownLatch latch = new CountDownLatch(1);
+
+        WorkerWithCountDownLatch worker1 = new WorkerWithCountDownLatch("Worker with latch 1", latch);
+        WorkerWithCountDownLatch worker2 = new WorkerWithCountDownLatch("Worker with latch 2", latch);
+
+        worker1.start();
+        worker2.start();
+
+        Thread.sleep(10);//simulation of some actual work
+
+        System.out.println("-----------------------------------------------");
+        System.out.println(" Now release the latch:");
+        System.out.println("-----------------------------------------------");
+        latch.countDown();
+    }
+
+    private static void usingCyclicBarrier() throws BrokenBarrierException, InterruptedException {
+        System.out.println("\n===============================================");
+        System.out.println("        >>> Using CyclicBarrier <<<<");
+        System.out.println("===============================================");
+
+        CyclicBarrier barrier = new CyclicBarrier(3);
+
+        WorkerWithCyclicBarrier worker1 = new WorkerWithCyclicBarrier("Worker with barrier 1", barrier);
+        WorkerWithCyclicBarrier worker2 = new WorkerWithCyclicBarrier("Worker with barrier 2", barrier);
+
+        worker1.start();
+        worker2.start();
+
+        Thread.sleep(10);//simulation of some actual work
+
+        System.out.println("-----------------------------------------------");
+        System.out.println(" Now open the barrier:");
+        System.out.println("-----------------------------------------------");
+        barrier.await();
+    }
+
+}

core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/threadsstartatsametime/WorkerWithCountDownLatch.java

@@ -0,0 +1,24 @@
+package com.baeldung.threadsstartatsametime;
+
+import java.time.Instant;
+import java.util.concurrent.CountDownLatch;
+
+public class WorkerWithCountDownLatch extends Thread {
+    private CountDownLatch latch;
+
+    public WorkerWithCountDownLatch(String name, CountDownLatch latch) {
+        this.latch = latch;
+        setName(name);
+    }
+
+    @Override public void run() {
+        try {
+            System.out.printf("[ %s ] created, blocked by the latch\n", getName());
+            latch.await();
+            System.out.printf("[ %s ] starts at: %s\n", getName(), Instant.now());
+            // do actual work here...
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/threadsstartatsametime/WorkerWithCyclicBarrier.java

@@ -0,0 +1,25 @@
+package com.baeldung.threadsstartatsametime;
+
+import java.time.Instant;
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CyclicBarrier;
+
+public class WorkerWithCyclicBarrier extends Thread {
+    private CyclicBarrier barrier;
+
+    public WorkerWithCyclicBarrier(String name, CyclicBarrier barrier) {
+        this.barrier = barrier;
+        this.setName(name);
+    }
+
+    @Override public void run() {
+        try {
+            System.out.printf("[ %s ] created, blocked by the barrier\n", getName());
+            barrier.await();
+            System.out.printf("[ %s ] starts at: %s\n", getName(), Instant.now());
+            // do actual work here...
+        } catch (InterruptedException | BrokenBarrierException e) {
+            e.printStackTrace();
+        }
+    }
+}