/*
 * 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/publicdomain/zero/1.0/
 */

import jsr166y.*;
import extra166y.*;
import java.util.*;
import java.util.concurrent.*;

public class MapReduceDemo {
    static final int NCPU = Runtime.getRuntime().availableProcessors();
    static final Random rng = new Random();

    /**
     * Sequential version, for performance comparison
     */
    static <T,U> U seqMapReduce(T[] array,
                                Ops.Op<T,U> mapper,
                                Ops.Reducer<U> reducer,
                                U base) {
        int n = array.length;
        U x = base;
        for (int i = 0; i < n; ++i)
            x = reducer.op(x, mapper.op(array[i]));
        return x;
    }



    // sample functions
    static final class GetNext implements Ops.Op<Rand, Long> {
        public Long op(Rand x) {
            return x.next();
        }
    }

    static final class Accum implements Ops.Reducer<Long> {
        public Long op(Long a, Long b) {
            long x = a;
            long y = b;
            return x + y;
        }
    }

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

    public static void main(String[] args) throws Exception {
        int n = 1 << 18;
        int reps = 1 << 8;
        Rand[] array = new Rand[n];
        for (int i = 0; i < n; ++i)
            array[i] = new Rand(i+1);
        ForkJoinPool fjp = new ForkJoinPool();
        ParallelArray<Rand> pa = ParallelArray.createUsingHandoff(array, fjp);
        final GetNext getNext = new GetNext();
        final Accum accum = new Accum();
        final Long zero = Long.valueOf(0);
        long last, now;
        double elapsed;
        for (int j = 0; j < 2; ++j) {
            long rseed = rng.nextLong();
            resetSeeds(array, rseed);
            long seqsum = 0;
            last = System.nanoTime();
            for (int k = 0; k < reps; ++k) {
                seqsum += seqMapReduce(array, getNext, accum, zero);
                Rand tmp = array[k];
                array[k] = array[n - k - 1];
                array[n - k - 1] = tmp;
            }
            now = System.nanoTime();
            elapsed = (double)(now - last) / NPS;
            last = now;
            System.out.printf("sequential:    %7.3f\n", elapsed);
            for (int i = 2; i <= NCPU; i <<= 1) {
                resetSeeds(array, rseed);
                long sum = 0;
                //                fjp.setParallelism(i);
                last = System.nanoTime();
                for (int k = 0; k < reps; ++k) {
                    sum += pa.withMapping(getNext).reduce(accum, zero);
                    Rand tmp = array[k];
                    array[k] = array[n - k - 1];
                    array[n - k - 1] = tmp;
                }
                now = System.nanoTime();
                elapsed = (double)(now - last) / NPS;
                last = now;
                System.out.printf("poolSize %3d:  %7.3f\n", fjp.getParallelism(), elapsed);
                if (sum != seqsum) throw new Error("checksum");
            }
            for (int i = NCPU; i >= 1; i >>>= 1) {
                resetSeeds(array, rseed);
                long sum = 0;
                //                fjp.setParallelism(i);
                last = System.nanoTime();
                for (int k = 0; k < reps; ++k) {
                    sum += pa.withMapping(getNext).reduce(accum, zero);
                    Rand tmp = array[k];
                    array[k] = array[n - k - 1];
                    array[n - k - 1] = tmp;
                }
                now = System.nanoTime();
                elapsed = (double)(now - last) / NPS;
                last = now;
                System.out.printf("poolSize %3d:  %7.3f\n", fjp.getParallelism(), elapsed);
                if (sum != seqsum) throw new Error("checksum");
            }
        }
        fjp.shutdownNow();
        fjp.awaitTermination(1, TimeUnit.SECONDS);
        Thread.sleep(100);
    }

    static void resetSeeds(Rand[] array, long s) {
        for (int i = 0; i < array.length; ++i)
            array[i].seed = s++;
    }

    /**
     * Xorshift Random algorithm.
     */
    public static final class Rand {
        private long seed;
        Rand(long s) {
            seed = s;
        }
        public long next() {
            long x = seed;
            x ^= x << 13;
            x ^= x >>> 7;
            x ^= (x << 17);
            seed = x;
            return x;
        }
    }

}