From 2bb31e54ed12726658333d4f7e307bf77a9413db Mon Sep 17 00:00:00 2001
From: Chandravadan S <s.chandravadan@gmail.com>
Date: Mon, 26 Jun 2017 14:42:00 +0530
Subject: [PATCH] Cyclic Barriers demo (#2156)

---
 .../cyclicbarrier/CyclicBarrierDemo.java      | 86 +++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 core-java/src/main/java/com/baeldung/concurrent/cyclicbarrier/CyclicBarrierDemo.java

diff --git a/core-java/src/main/java/com/baeldung/concurrent/cyclicbarrier/CyclicBarrierDemo.java b/core-java/src/main/java/com/baeldung/concurrent/cyclicbarrier/CyclicBarrierDemo.java
new file mode 100644
index 0000000000..69b6d46599
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/concurrent/cyclicbarrier/CyclicBarrierDemo.java
@@ -0,0 +1,86 @@
+package com.baeldung.concurrent.cyclicbarrier;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CyclicBarrier;
+
+/**
+ * Created by cv on 24/6/17.
+ */
+public class CyclicBarrierDemo {
+
+    private CyclicBarrier cyclicBarrier;
+    private List<List<Integer>> partialResults = Collections.synchronizedList(new ArrayList<>());
+    private Random random = new Random();
+    private int NUM_PARTIAL_RESULTS;
+    private int NUM_WORKERS;
+
+
+    public void runSimulation(int numWorkers, int numberOfPartialResults) {
+        NUM_PARTIAL_RESULTS = numberOfPartialResults;
+        NUM_WORKERS = numWorkers;
+
+        cyclicBarrier = new CyclicBarrier(NUM_WORKERS, new AggregatorThread());
+        System.out.println("Spawning " + NUM_WORKERS + " worker threads to compute "
+                + NUM_PARTIAL_RESULTS + " partial results each");
+        for (int i = 0; i < NUM_WORKERS; i++) {
+            Thread worker = new Thread(new NumberCruncherThread());
+            worker.setName("Thread " + i);
+            worker.start();
+        }
+    }
+
+    class NumberCruncherThread implements Runnable {
+
+        @Override
+        public void run() {
+            String thisThreadName = Thread.currentThread().getName();
+            List<Integer> partialResult = new ArrayList<>();
+            for (int i = 0; i < NUM_PARTIAL_RESULTS; i++) {
+                Integer num = random.nextInt(10);
+                System.out.println(thisThreadName
+                        + ": Crunching some numbers! Final result - " + num);
+                partialResult.add(num);
+            }
+            partialResults.add(partialResult);
+            try {
+                System.out.println(thisThreadName + " waiting for others to reach barrier.");
+                cyclicBarrier.await();
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            } catch (BrokenBarrierException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    class AggregatorThread implements Runnable {
+
+        @Override
+        public void run() {
+            String thisThreadName = Thread.currentThread().getName();
+            System.out.println(thisThreadName + ": Computing final sum of " + NUM_WORKERS
+                    + " workers, having " + NUM_PARTIAL_RESULTS + " results each.");
+            int sum = 0;
+            for (List<Integer> threadResult : partialResults) {
+                System.out.print("Adding ");
+                for (Integer partialResult : threadResult) {
+                    System.out.print(partialResult+" ");
+                    sum += partialResult;
+                }
+                System.out.println();
+            }
+            System.out.println(Thread.currentThread().getName() + ": Final result = " + sum);
+        }
+
+    }
+
+    public static void main(String[] args) {
+        CyclicBarrierDemo play = new CyclicBarrierDemo();
+        play.runSimulation(5, 3);
+    }
+
+}