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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/licenses/publicdomain |
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*/ |
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|
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//import jsr166y.*; |
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import java.util.*; |
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import java.util.concurrent.*; |
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|
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public final class DynamicLeftSpineFib extends RecursiveAction { |
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|
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// Performance-tuning constant: |
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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 = 43; |
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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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} |
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catch (Exception e) { |
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System.out.println("Usage: java DynamicLeftSpineFib <threads> <number> [<sequentialThreshold>]"); |
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return; |
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} |
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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) ? |
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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 < 10; ++i) { |
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test(g, num); |
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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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static void test(ForkJoinPool g, int num) throws Exception { |
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int ps = g.getParallelism(); |
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long start = System.currentTimeMillis(); |
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DynamicLeftSpineFib f = new DynamicLeftSpineFib(num, null); |
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g.invoke(f); |
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long time = System.currentTimeMillis() - start; |
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double secs = (double) time / 1000.0; |
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long result = f.getAnswer(); |
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System.out.print("DynamicLeftSpineFib " + num + " = " + result); |
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System.out.printf("\tTime: %7.3f", secs); |
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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: %8d", g.getPoolSize()); |
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System.out.println(); |
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} |
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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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DynamicLeftSpineFib next; |
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|
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DynamicLeftSpineFib(int n, DynamicLeftSpineFib nxt) { |
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number = n; next = nxt; |
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} |
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|
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int getAnswer() { |
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return number; |
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} |
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|
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public final void compute() { |
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int n = number; |
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if (n > 1) { |
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DynamicLeftSpineFib rt = null; |
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while (n > 1 && getSurplusQueuedTaskCount() <= 3) { |
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(rt = new DynamicLeftSpineFib(n - 2, rt)).fork(); |
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n -= 1; |
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} |
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int r = seqFib(n); |
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while (rt != null) { |
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if (rt.tryUnfork()) rt.compute(); else rt.helpJoin(); |
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r += rt.number; |
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rt = rt.next; |
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} |
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number = r; |
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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 int seqFib(int n) { |
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if (n <= 1) |
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return n; |
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else |
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return seqFib(n-1) + seqFib(n-2); |
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} |
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|
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} |
