Java example source code file (ThreadLessCommon.java)

This example Java source code file (ThreadLessCommon.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

assertionerror, exception, expected, forkjoinworkerthreadfactory, long, nullforkjoinworkerthreadfactory, object, override, recursivetask, string, sumtask, threading, threadlesscommon, threads, threshold, throwable

The ThreadLessCommon.java Java example source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * 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/
 */

/*
 * @test
 * @bug 8008378
 * @summary Basic checks for parallelism 0, and null returning factory
 * @run main/othervm -Djava.util.concurrent.ForkJoinPool.common.parallelism=0 ThreadLessCommon
 * @run main/othervm -Djava.util.concurrent.ForkJoinPool.common.threadFactory=ThreadLessCommon$NullForkJoinWorkerThreadFactory ThreadLessCommon
 * @author Chris Hegarty
 */

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
import java.util.concurrent.ForkJoinWorkerThread;
import java.util.concurrent.RecursiveTask;

public class ThreadLessCommon {

    static final int THRESHOLD = 1000;
    static final boolean debug = true;

    private static void realMain(String[] args) throws Throwable {
        if (debug) {
            String pp = System.getProperty(
                    "java.util.concurrent.ForkJoinPool.common.parallelism");
            System.out.println(
                    "java.util.concurrent.ForkJoinPool.common.parallelism:" + pp);
            String tf = System.getProperty(
                    "java.util.concurrent.ForkJoinPool.common.threadFactory");
            System.out.println(
                    "java.util.concurrent.ForkJoinPool.common.threadFactory:" + tf);
        }

        long from = 0, to = 50000;
        RecursiveTask<Long> task = new SumTask(from, to, Thread.currentThread());
        long sum = task.invoke();
        System.out.printf("%nSum: from [%d] to [%d] = [%d]%n", from, to, sum);

        task.fork();
        sum = task.join();
        System.out.printf("%nSum: from [%d] to [%d] = [%d]%n", from, to, sum);

        sum = ForkJoinPool.commonPool().invoke(task.fork());
        System.out.printf("%nSum: from [%d] to [%d] = [%d]%n", from, to, sum);
    }

    static class SumTask extends RecursiveTask<Long> {
        final Thread expectedThread;
        final long from;
        final long to;
        SumTask(long from, long to, Thread thread) {
            this.from = from; this.to = to; expectedThread = thread;
        }

        @Override
        public Long compute() {
            check(Thread.currentThread() == expectedThread,
                  "Expected " + expectedThread + ", got " + Thread.currentThread());
            long range = to - from;
            if (range < THRESHOLD) {
                long acc = 0;
                for (long i = from; i <= to; i++)
                    acc = acc + i;
                return acc;
            } else {
                long half = from + range / 2;
                SumTask t1 = new SumTask(from, half ,expectedThread);
                SumTask t2 = new SumTask(half+1, to ,expectedThread);
                if (half % 2 == 0) {
                    t1.fork();
                    return t2.compute() + t1.join();
                } else {
                    invokeAll(t1, t2);
                    try { return t1.get() + t2.get(); }
                    catch (Exception x) { unexpected(x); return 0L;}
                }
            }
        }
    }

    public static class NullForkJoinWorkerThreadFactory
        implements ForkJoinWorkerThreadFactory
    {
        @Override
        public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
            return null;
        }
    }

    //--------------------- Infrastructure ---------------------------
    static volatile int passed = 0, failed = 0;
    static void pass() {passed++;}
    static void fail() {failed++; /*Thread.dumpStack();*/}
    static void fail(String msg) {System.out.println(msg); fail();}
    static void unexpected(Throwable t) {failed++; t.printStackTrace();}
    static void check(boolean cond, String msg) {if (cond) pass(); else fail(msg);}
    static void equal(Object x, Object y) {
        if (x == null ? y == null : x.equals(y)) pass();
        else fail(x + " not equal to " + y);}
    public static void main(String[] args) throws Throwable {
        try {realMain(args);} catch (Throwable t) {unexpected(t);}
        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
        if (failed > 0) throw new AssertionError("Some tests failed");}
}