add Phaser implementations (#11051)

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

@@ -3,6 +3,7 @@ package com.baeldung.threadsstartatsametime;
 import java.util.concurrent.BrokenBarrierException;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.CyclicBarrier;
+import java.util.concurrent.Phaser;
 
 public class ThreadsStartAtSameTime {
 
@@ -12,6 +13,11 @@ public class ThreadsStartAtSameTime {
         Thread.sleep(30);
 
         usingCyclicBarrier();
+
+        Thread.sleep(30);
+
+        usingPhaser();
+
     }
 
     private static void usingCountDownLatch() throws InterruptedException {
@@ -56,4 +62,25 @@ public class ThreadsStartAtSameTime {
         barrier.await();
     }
 
+    private static void usingPhaser() throws InterruptedException {
+        System.out.println("\n===============================================");
+        System.out.println("        >>> Using Phaser <<<");
+        System.out.println("===============================================");
+
+        Phaser phaser = new Phaser();
+        phaser.register();
+
+        WorkerWithPhaser worker1 = new WorkerWithPhaser("Worker with phaser 1", phaser);
+        WorkerWithPhaser worker2 = new WorkerWithPhaser("Worker with phaser 2", phaser);
+
+        worker1.start();
+        worker2.start();
+
+        Thread.sleep(10);//simulation of some actual work
+
+        System.out.println("-----------------------------------------------");
+        System.out.println(" Now open the phaser barrier:");
+        System.out.println("-----------------------------------------------");
+        phaser.arriveAndAwaitAdvance();
+    }
 }

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

@@ -0,0 +1,26 @@
+package com.baeldung.threadsstartatsametime;
+
+import java.time.Instant;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Phaser;
+
+public class WorkerWithPhaser extends Thread {
+    private Phaser phaser;
+
+    public WorkerWithPhaser(String name, Phaser phaser) {
+        this.phaser = phaser;
+        phaser.register();
+        setName(name);
+    }
+
+    @Override public void run() {
+        try {
+            System.out.printf("[ %s ] created, blocked by the phaser\n", getName());
+            phaser.arriveAndAwaitAdvance();
+            System.out.printf("[ %s ] starts at: %s\n", getName(), Instant.now());
+            // do actual work here...
+        } catch (IllegalStateException e) {
+            e.printStackTrace();
+        }
+    }
+}