test/loops/NQueensCS.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

//import jsr166y.*;
import java.util.*;
import java.util.concurrent.*;

public final class NQueensCS extends RecursiveAction {

    static long lastStealCount;
    static int boardSize;

    static final int[] expectedSolutions = new int[] {
        0, 1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2680, 14200,
        73712, 365596, 2279184, 14772512, 95815104, 666090624
    }; // see http://www.durangobill.com/N_Queens.html

    static final int FIRST_SIZE = 8; // smaller ones too short to measure well
    static final int LAST_SIZE = 15; // bigger ones too long to wait for

    /** for time conversion */
    static final long NPS = (1000L * 1000 * 1000);

    public static void main(String[] args) throws Exception {
        int procs = 0;
        try {
            if (args.length > 0)
                procs = Integer.parseInt(args[0]);
        }
        catch (Exception e) {
            System.out.println("Usage: java NQueensCS <threads> ");
            return;
        }
        for (int reps = 0; reps < 2; ++reps) {
            ForkJoinPool g = (procs == 0) ?
                new ForkJoinPool() :
                new ForkJoinPool(procs);
            lastStealCount = g.getStealCount();
            for (int i = FIRST_SIZE; i <= LAST_SIZE; i++)
                test(g, i);
            System.out.println(g);
            g.shutdown();
        }
    }

    static void test(ForkJoinPool g, int i) throws Exception {
        boardSize = i;
        int ps = g.getParallelism();
        long start = System.nanoTime();
        NQueensCS task = new NQueensCS(new int[0]);
        g.invoke(task);
        int solutions = task.solutions;
        long time = System.nanoTime() - start;
        double secs = ((double)time) / NPS;
        if (solutions != expectedSolutions[i])
            throw new Error();
        System.out.printf("NQueensCS %3d", i);
        System.out.printf(" Time: %7.3f", secs);
        long sc = g.getStealCount();
        long ns = sc - lastStealCount;
        lastStealCount = sc;
        System.out.printf(" Steals/t: %5d", ns/ps);
        System.out.println();
    }

    // Boards are represented as arrays where each cell
    // holds the column number of the queen in that row

    final int[] sofar;
    NQueensCS nextSubtask; // to link subtasks
    int solutions;
    NQueensCS(int[] a) {
        this.sofar = a;
    }

    public final void compute() {
        NQueensCS subtasks;
        int bs = boardSize;
        if (sofar.length >= bs)
            solutions = 1;
        else if ((subtasks = explore(sofar, bs)) != null)
            solutions = processSubtasks(subtasks);
    }

    private static NQueensCS explore(int[] array, int bs) {
        int row = array.length;
        NQueensCS s = null; // subtask list
        outer:
        for (int q = 0; q < bs; ++q) {
            for (int i = 0; i < row; i++) {
                int p = array[i];
                if (q == p || q == p - (row - i) || q == p + (row - i))
                    continue outer; // attacked
            }
            NQueensCS first = s; // lag forks to ensure 1 kept
            if (first != null)
                first.fork();
            int[] next = Arrays.copyOf(array, row+1);
            next[row] = q;
            NQueensCS subtask = new NQueensCS(next);
            subtask.nextSubtask = first;
            s = subtask;
        }
        return s;
    }

    private static int processSubtasks(NQueensCS s) {
        // Always run first the task held instead of forked
        s.compute();
        int ns = s.solutions;
        s = s.nextSubtask;
        // Then the unstolen ones
        while (s != null && s.tryUnfork()) {
            s.compute();
            ns += s.solutions;
            s = s.nextSubtask;
        }
        // Then wait for the stolen ones
        while (s != null) {
            s.join();
            ns += s.solutions;
            s = s.nextSubtask;
        }
        return ns;
    }
}
Revision:	1.3
Committed:	Mon Nov 2 23:42:46 2009 UTC (14 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+2 -1 lines
Log Message:	whitespace
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
5	*/
6
7	//import jsr166y.*;
8	import java.util.*;
9	import java.util.concurrent.*;
10
11	public final class NQueensCS extends RecursiveAction {
12
13	static long lastStealCount;
14	static int boardSize;
15
16	static final int[] expectedSolutions = new int[] {
17	0, 1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2680, 14200,
18	73712, 365596, 2279184, 14772512, 95815104, 666090624
19	}; // see http://www.durangobill.com/N_Queens.html
20
21	static final int FIRST_SIZE = 8; // smaller ones too short to measure well
22	static final int LAST_SIZE = 15; // bigger ones too long to wait for
23
24	/** for time conversion */
25	static final long NPS = (1000L * 1000 * 1000);
26
27	public static void main(String[] args) throws Exception {
28	int procs = 0;
29	try {
30	if (args.length > 0)
31	procs = Integer.parseInt(args[0]);
32	}
33	catch (Exception e) {
34	System.out.println("Usage: java NQueensCS <threads> ");
35	return;
36	}
37	for (int reps = 0; reps < 2; ++reps) {
38	ForkJoinPool g = (procs == 0) ?
39	new ForkJoinPool() :
40	new ForkJoinPool(procs);
41	lastStealCount = g.getStealCount();
42	for (int i = FIRST_SIZE; i <= LAST_SIZE; i++)
43	test(g, i);
44	System.out.println(g);
45	g.shutdown();
46	}
47	}
48
49	static void test(ForkJoinPool g, int i) throws Exception {
50	boardSize = i;
51	int ps = g.getParallelism();
52	long start = System.nanoTime();
53	NQueensCS task = new NQueensCS(new int[0]);
54	g.invoke(task);
55	int solutions = task.solutions;
56	long time = System.nanoTime() - start;
57	double secs = ((double)time) / NPS;
58	if (solutions != expectedSolutions[i])
59	throw new Error();
60	System.out.printf("NQueensCS %3d", i);
61	System.out.printf(" Time: %7.3f", secs);
62	long sc = g.getStealCount();
63	long ns = sc - lastStealCount;
64	lastStealCount = sc;
65	System.out.printf(" Steals/t: %5d", ns/ps);
66	System.out.println();
67	}
68
69	// Boards are represented as arrays where each cell
70	// holds the column number of the queen in that row
71
72	final int[] sofar;
73	NQueensCS nextSubtask; // to link subtasks
74	int solutions;
75	NQueensCS(int[] a) {
76	this.sofar = a;
77	}
78
79	public final void compute() {
80	NQueensCS subtasks;
81	int bs = boardSize;
82	if (sofar.length >= bs)
83	solutions = 1;
84	else if ((subtasks = explore(sofar, bs)) != null)
85	solutions = processSubtasks(subtasks);
86	}
87
88	private static NQueensCS explore(int[] array, int bs) {
89	int row = array.length;
90	NQueensCS s = null; // subtask list
91	outer:
92	for (int q = 0; q < bs; ++q) {
93	for (int i = 0; i < row; i++) {
94	int p = array[i];
95	if (q == p \|\| q == p - (row - i) \|\| q == p + (row - i))
96	continue outer; // attacked
97	}
98	NQueensCS first = s; // lag forks to ensure 1 kept
99	if (first != null)
100	first.fork();
101	int[] next = Arrays.copyOf(array, row+1);
102	next[row] = q;
103	NQueensCS subtask = new NQueensCS(next);
104	subtask.nextSubtask = first;
105	s = subtask;
106	}
107	return s;
108	}
109
110	private static int processSubtasks(NQueensCS s) {
111	// Always run first the task held instead of forked
112	s.compute();
113	int ns = s.solutions;
114	s = s.nextSubtask;
115	// Then the unstolen ones
116	while (s != null && s.tryUnfork()) {
117	s.compute();
118	ns += s.solutions;
119	s = s.nextSubtask;
120	}
121	// Then wait for the stolen ones
122	while (s != null) {
123	s.join();
124	ns += s.solutions;
125	s = s.nextSubtask;
126	}
127	return ns;
128	}
129	}