ForkJoin API

gistfile1.java

package de.michaelwellner.edu.forkjoin;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

public class ForkJoin {

  private static final boolean DEBUG = false;

	private static class Fibonacci {

		private final int n;

		public Fibonacci(int n) {
			this.n = n;
		}

		public long solve() {
			return this.fibonacci(this.n);
		}

		private long fibonacci(int n) {
			if (DEBUG)
				System.out.println("Thread " + Thread.currentThread().getName()
						+ " calculates " + "fibonacci for " + n);

			if (n <= 1) {
				return n;
			} else {
				return fibonacci(n - 1) + fibonacci(n - 2);
			}
		}

		public int getN() {
			return n;
		}

	}

	private static class FibonacciTask extends RecursiveTask<Long> {

		private static final long serialVersionUID = 5085586289180387451L;

		private static final int THRESHOLD = 5;

		private final Fibonacci fibonacci;

		public FibonacciTask(Fibonacci fibonacci) {
			this.fibonacci = fibonacci;
		}

		@Override
		protected Long compute() {
			if (this.fibonacci.getN() <= THRESHOLD) {
				return this.fibonacci.solve();
			} else {
				final FibonacciTask f1 = new FibonacciTask(new Fibonacci(
						this.fibonacci.getN() - 1));
				final FibonacciTask f2 = new FibonacciTask(new Fibonacci(
						this.fibonacci.getN() - 2));
				f1.fork();
				return f2.compute() + f1.join();
			}
		}

	}

	public static void main(String... args) {
		final int n = 10;
		classic(n);
		System.out.println("\n\n\n");
		forkjoin(n);
	}

	private static void forkjoin(final int n) {
		final int processors = Runtime.getRuntime().availableProcessors();
		System.out.println("Available Processors: " + processors);

		final Fibonacci f = new Fibonacci(n);
		final ForkJoinPool pool = new ForkJoinPool(processors);

		final long elapsedTime = stopWatch(new Runnable() {

			@Override
			public void run() {
				System.out.println("Calculating fibonacci(" + n + ")");

				final FibonacciTask task = new FibonacciTask(f);
				long result = pool.invoke(task);

				System.out.println("Result: " + result);
			}

		});

		System.out.println("Elapsed Time: " + elapsedTime + "ms");
	}

	private static void classic(final int n) {
		final Fibonacci f = new Fibonacci(n);
		final long elapsedTime = stopWatch(new Runnable() {

			@Override
			public void run() {
				System.out.println("Calculating fibonacci(" + n + ")");
				System.out.println("Result: " + f.solve());
			}

		});

		System.out.println("Elapsed Time: " + elapsedTime + "ms");
	}

	private static long stopWatch(Runnable runnable) {
		long start = System.currentTimeMillis();
		runnable.run();
		return (System.currentTimeMillis() - start);
	}

}