/*
 * 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 java.util.concurrent.Phaser;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicLong;
//import java.util.concurrent.atomic.LongAdder;
import jsr166e.LongAdder;

public class LongAdderDemo {
    static final int INCS_PER_THREAD = 10000000;
    static final int NCPU = Runtime.getRuntime().availableProcessors();
    static final ExecutorService pool = Executors.newCachedThreadPool();

    public static void main(String[] args) {
        System.out.println("Warmup...");
        int half = NCPU > 1 ? NCPU / 2 : 1;
        //        casTest(half, 1000);
        adderTest(half, 1000);

        for (int reps = 0; reps < 2; ++reps) {
            System.out.println("Running...");
            for (int i = 1; i <= NCPU * 2; i <<= 1) {
                //                casTest(i, INCS_PER_THREAD);
                adderTest(i, INCS_PER_THREAD);
            }
        }
        pool.shutdown();
    }

    static void casTest(int nthreads, int incs) {
        System.out.print("AtomicLong ");
        Phaser phaser = new Phaser(nthreads + 1);
        AtomicLong a = new AtomicLong();
        for (int i = 0; i < nthreads; ++i)
            pool.execute(new CasTask(a, phaser, incs));
        report(nthreads, incs, timeTasks(phaser), a.get());
    }

    static void adderTest(int nthreads, int incs) {
        System.out.print("LongAdder  ");
        Phaser phaser = new Phaser(nthreads + 1);
        LongAdder a = new LongAdder();
        for (int i = 0; i < nthreads; ++i)
            pool.execute(new AdderTask(a, phaser, incs));
        report(nthreads, incs, timeTasks(phaser), a.sum());
    }

    static void report(int nthreads, int incs, long time, long sum) {
        long total = (long)nthreads * incs;
        if (sum != total)
            throw new Error(sum + " != " + total);
        double secs = (double)time / (1000L * 1000 * 1000);
        long rate = total * (1000L) / time;
        System.out.printf("threads:%3d  Time: %7.3fsec  Incs per microsec: %4d\n",
                          nthreads, secs, rate);
    }

    static long timeTasks(Phaser phaser) {
        phaser.arriveAndAwaitAdvance();
        long start = System.nanoTime();
        phaser.arriveAndAwaitAdvance();
        phaser.arriveAndAwaitAdvance();
        return System.nanoTime() - start;
    }

    static final class AdderTask implements Runnable {
        final LongAdder adder;
        final Phaser phaser;
        final int incs;
        volatile long result;
        AdderTask(LongAdder adder, Phaser phaser, int incs) {
            this.adder = adder;
            this.phaser = phaser;
            this.incs = incs;
        }

        public void run() {
            phaser.arriveAndAwaitAdvance();
            phaser.arriveAndAwaitAdvance();
            LongAdder a = adder;
            for (int i = 0; i < incs; ++i)
                a.increment();
            result = a.sum();
            phaser.arrive();
        }
    }

    static final class CasTask implements Runnable {
        final AtomicLong adder;
        final Phaser phaser;
        final int incs;
        volatile long result;
        CasTask(AtomicLong adder, Phaser phaser, int incs) {
            this.adder = adder;
            this.phaser = phaser;
            this.incs = incs;
        }

        public void run() {
            phaser.arriveAndAwaitAdvance();
            phaser.arriveAndAwaitAdvance();
            AtomicLong a = adder;
            for (int i = 0; i < incs; ++i)
                a.getAndIncrement();
            result = a.get();
            phaser.arrive();
        }
    }

}