06. Fibonacci Fork/Join

README.md

@@ -13,8 +13,11 @@
 
 ### Introduce to ForkJoin Framework
 * ArraySum using Recursive Action
+* Fibonacci Using Recursive Task
 
 ### Acknowledgments
 Inspiration, code snippets, etc.
 * [Java - MultiThreading](https://www.youtube.com/watch?v=9DvDheKRJ9Y&t=656s)
 * [Java - Executor Service](https://jenkov.com/tutorials/java-util-concurrent/executorservice.html)
+* [Recursive Task](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/RecursiveTask.html)
+* [Parallel Programming in Java] (https://www.coursera.org/learn/parallel-programming-in-java)
\ No newline at end of file

src/main/java/Fibonacci.java

+import java.util.concurrent.RecursiveTask;
+
+
+/*
+However, besides being a dumb way to compute Fibonacci functions (there is a simple fast linear algorithm that you'd use in practice),
+ this is likely to perform poorly because the smallest subtasks are too small to be worthwhile splitting up.
+ Instead, as is the case for nearly all fork/join applications,
+ you'd pick some minimum granularity size (for example 10 here) for which you always sequentially solve rather than subdividing.
+ */
+
+public class Fibonacci extends RecursiveTask<Integer> {
+    final int n;
+    public Fibonacci(int n) { this.n = n; }
+
+    public Integer compute() {
+
+        if(n > 20) {
+            if (n <= 1)
+                return n;
+            Fibonacci f1 = new Fibonacci(n - 1);
+            f1.fork();
+            Fibonacci f2 = new Fibonacci(n - 2);
+            return f2.compute() + f1.join();
+        }else{
+            return computeSeq();
+        }
+    }
+
+    public Integer computeSeq() {
+        if (n <= 1)
+            return n;
+        Fibonacci f1 = new Fibonacci(n - 1);
+        Fibonacci f2 = new Fibonacci(n - 2);
+        return f2.computeSeq() + f1.computeSeq();
+    }
+
+}

src/test/java/FibonacciTest.java

+import junit.framework.TestCase;
+
+
+public class FibonacciTest extends TestCase {
+
+    int n=40;
+
+    public void testFiboPP(){
+        long start = System.currentTimeMillis();
+        Fibonacci fib = new Fibonacci(n);
+        int res = fib.compute();
+        long end = System.currentTimeMillis()-start;
+        System.out.printf("Fibonacci for %d is %d, and parallel execution took %d ms\n",n,res,end);
+//        Fibonacci parallel takes 144269 fon n = 50 before enhancement 1
+    }
+
+    public void testFiboSeq(){
+        long start = System.currentTimeMillis();
+        Fibonacci fib = new Fibonacci(n);
+        int res = fib.computeSeq();
+        long end = System.currentTimeMillis()-start;
+        System.out.printf("Fibonacci for %d is %d, and sequential execution took %d ms\n",n,res,end);
+        //Fibonacci Sequential takes 86495 fon n = 50 before enhancement 1
+    }
+}