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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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public final class DynamicFib extends RecursiveAction { |
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static int procs; |
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static long lastStealCount; // to display steal counts |
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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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public static void main(String[] args) throws Exception { |
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procs = 0; |
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int num = 45; |
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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 DynamicFib <threads> <number>"); |
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return; |
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} |
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for (int reps = 0; reps < 2; ++reps) { |
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ForkJoinPool pool = (procs == 0) ? new ForkJoinPool() : |
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new ForkJoinPool(procs); |
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for (int i = 0; i < 20; ++i) |
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test(pool, num); |
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System.out.println(pool); |
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pool.shutdown(); |
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} |
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} |
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|
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static void test(ForkJoinPool pool, int num) throws Exception { |
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int ps = pool.getParallelism(); |
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long start = System.nanoTime(); |
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DynamicFib f = new DynamicFib(num); |
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pool.invoke(f); |
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long time = System.nanoTime() - start; |
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double secs = ((double)time) / NPS; |
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long result = f.number; |
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System.out.print("DynamicFib " + num + " = " + result); |
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System.out.printf("\tTime: %9.3f", secs); |
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long sc = pool.getStealCount(); |
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long ns = sc - lastStealCount; |
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lastStealCount = sc; |
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System.out.printf(" Steals: %4d", ns/ps); |
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System.out.printf(" Workers: %4d", pool.getPoolSize()); |
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System.out.println(); |
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} |
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|
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int number; // Initialized with argument; replaced with result |
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DynamicFib(int n) { number = n; } |
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public void compute() { |
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number = fib(number); |
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} |
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|
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static int fib(int n) { |
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int res; |
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if (n <= 1) |
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res = n; |
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else if (getSurplusQueuedTaskCount() >= 4) |
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res = seqFib(n); |
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else { |
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DynamicFib f2 = new DynamicFib(n - 2); |
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f2.fork(); |
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res = fib(n - 1); |
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if (f2.tryUnfork()) |
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res += fib(n - 2); |
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else { |
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f2.quietlyJoin(); |
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res += f2.number; |
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} |
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} |
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return res; |
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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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|
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} |
