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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.*; |
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import java.util.concurrent.*; |
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import java.util.concurrent.atomic.*; |
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|
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public final class AsyncNQueensCS extends LinkedAsyncAction { |
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|
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static long lastStealCount; |
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static int boardSize; |
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|
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static final int[] expectedSolutions = new int[] { |
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0, 1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2680, 14200, |
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73712, 365596, 2279184, 14772512, 95815104, 666090624 |
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}; // see http://www.durangobill.com/N_Queens.html |
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|
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static final int FIRST_SIZE = 8; // smaller ones too short to measure well |
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static final int LAST_SIZE = 15; // bigger ones too long to wait for |
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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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int procs = 0; |
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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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} |
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catch (Exception e) { |
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System.out.println("Usage: java AsyncNQueensCS <threads> "); |
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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 g = (procs == 0) ? new ForkJoinPool() : |
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new ForkJoinPool(procs); |
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System.out.println("Number of procs=" + g.getParallelism()); |
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lastStealCount = g.getStealCount(); |
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for (int i = FIRST_SIZE; i <= LAST_SIZE; i++) |
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test(g, i); |
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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 i) throws Exception { |
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boardSize = i; |
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int ps = g.getParallelism(); |
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long start = System.nanoTime(); |
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AsyncNQueensCS task = new AsyncNQueensCS(null, new int[0]); |
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g.invoke(task); |
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int solutions = task.solutions; |
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long time = System.nanoTime() - start; |
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double secs = ((double)time) / NPS; |
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if (solutions != expectedSolutions[i]) |
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throw new Error(); |
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System.out.printf("AsyncNQueensCS %3d", i); |
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System.out.printf(" Time: %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.println(); |
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} |
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|
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// Boards are represented as arrays where each cell |
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// holds the column number of the queen in that row |
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|
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final int[] sofar; |
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volatile int solutions; |
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AsyncNQueensCS(AsyncNQueensCS parent, int[] a) { |
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super(parent); |
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this.sofar = a; |
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} |
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|
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public final boolean exec() { |
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int bs = boardSize; |
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int row = sofar.length; |
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if (row >= bs) |
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solutions = 1; |
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else { |
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outer: |
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for (int q = 0; q < bs; ++q) { |
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for (int i = 0; i < row; i++) { |
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int p = sofar[i]; |
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if (q == p || q == p - (row - i) || q == p + (row - i)) |
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continue outer; // attacked |
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} |
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int[] next = Arrays.copyOf(sofar, row+1); |
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next[row] = q; |
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new AsyncNQueensCS(this, next).fork(); |
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} |
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} |
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complete(); |
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return false; |
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} |
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|
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protected void onCompletion() { |
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LinkedAsyncAction p; |
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int n = solutions; |
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if (n != 0 && (p = getParent()) != null) |
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solutionUpdater.addAndGet((AsyncNQueensCS)p, n); |
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} |
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|
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static final AtomicIntegerFieldUpdater<AsyncNQueensCS> solutionUpdater = |
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AtomicIntegerFieldUpdater.newUpdater(AsyncNQueensCS.class, "solutions"); |
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} |
