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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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import java.util.concurrent.*; |
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|
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/** |
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* Recursive task-based version of Fibonacci. Computes: |
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* <pre> |
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* Computes fibonacci(n) = fibonacci(n-1) + fibonacci(n-2); for n> 1 |
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* fibonacci(0) = 0; |
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* fibonacci(1) = 1. |
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* </pre> |
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*/ |
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public final class FibTask extends RecursiveTask<Integer> { |
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|
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// Performance-tuning constant: |
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static int sequentialThreshold; |
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|
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static long lastStealCount; |
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|
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public static void main(String[] args) throws Exception { |
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int procs = 0; |
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int num = 45; |
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sequentialThreshold = 2; |
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try { |
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if (args.length > 0) |
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procs = Integer.parseInt(args[0]); |
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if (args.length > 1) |
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num = Integer.parseInt(args[1]); |
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if (args.length > 2) |
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sequentialThreshold = Integer.parseInt(args[2]); |
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} |
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catch (Exception e) { |
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System.out.println("Usage: java Fib <threads> <number> [<sequentialThreshold>]"); |
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return; |
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} |
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|
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for (int reps = 0; reps < 2; ++reps) { |
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ForkJoinPool g = (procs == 0) ? new ForkJoinPool() : |
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new ForkJoinPool(procs); |
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lastStealCount = g.getStealCount(); |
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for (int i = 0; i < 20; ++i) { |
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test(g, num); |
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// Thread.sleep(1000); |
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} |
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System.out.println(g); |
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g.shutdown(); |
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} |
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} |
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|
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/** for time conversion */ |
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static final long NPS = (1000L * 1000 * 1000); |
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|
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static void test(ForkJoinPool g, int num) throws Exception { |
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int ps = g.getParallelism(); |
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long start = System.nanoTime(); |
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int result = g.invoke(new FibTask(num)); |
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long time = System.nanoTime() - start; |
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double secs = ((double)time) / NPS; |
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System.out.print("FibTask " + num + " = " + result); |
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System.out.printf("\tTime: %7.3f", secs); |
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|
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long sc = g.getStealCount(); |
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long ns = sc - lastStealCount; |
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lastStealCount = sc; |
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System.out.printf(" Steals/t: %5d", ns/ps); |
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System.out.printf(" Workers: %5d", g.getPoolSize()); |
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System.out.println(); |
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} |
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|
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// Initialized with argument; replaced with result |
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int number; |
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|
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FibTask(int n) { number = n; } |
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|
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public Integer compute() { |
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int n = number; |
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|
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// Handle base cases: |
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if (n <= 1) { |
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return n; |
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} |
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// Use sequential code for small problems: |
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else if (n <= sequentialThreshold) { |
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return seqFib(n); |
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} |
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// Otherwise use recursive parallel decomposition: |
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else { |
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FibTask f1 = new FibTask(n - 1); |
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f1.fork(); |
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FibTask f2 = new FibTask(n - 2); |
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return f2.compute() + f1.join(); |
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} |
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} |
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|
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// Sequential version for arguments less than threshold |
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static final int seqFib(int n) { // unroll left only |
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int r = 1; |
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do { |
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int m = n - 2; |
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r += m <= 1 ? m : seqFib(m); |
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} while (--n > 1); |
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return r; |
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} |
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} |
