Java example source code file (FlakyMutex.java)

This example Java source code file (FlakyMutex.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

condition, cyclicbarrier, flakymutex, flakysync, interruptedexception, lock, myerror, myexception, myruntimeexception, object, random, suppresswarnings, threading, threads, throwable, util

The FlakyMutex.java Java example source code

/*
 * Copyright (c) 2006, 2013, Oracle and/or its affiliates. All rights reserved.
 * 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.
 */

/*
 * @test
 * @bug 6503247 6574123
 * @summary Test resilience to tryAcquire methods that throw
 * @author Martin Buchholz
 */

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

/**
 * This uses a variant of the standard Mutex demo, except with a
 * tryAcquire method that randomly throws various Throwable
 * subclasses.
 */
@SuppressWarnings("serial")
public class FlakyMutex implements Lock {
    static class MyError extends Error {}
    static class MyException extends Exception {}
    static class MyRuntimeException extends RuntimeException {}

    static final Random rnd = new Random();

    static void maybeThrow() {
        switch (rnd.nextInt(10)) {
        case 0: throw new MyError();
        case 1: throw new MyRuntimeException();
        case 2: FlakyMutex.<RuntimeException>uncheckedThrow(new MyException());
        default: /* Do nothing */ break;
        }
    }

    static void checkThrowable(Throwable t) {
        check((t instanceof MyError) ||
              (t instanceof MyException) ||
              (t instanceof MyRuntimeException));
    }

    static void realMain(String[] args) throws Throwable {
        final int nThreads = 3;
        final CyclicBarrier barrier = new CyclicBarrier(nThreads + 1);
        final FlakyMutex m = new FlakyMutex();
        final ExecutorService es = Executors.newFixedThreadPool(nThreads);
        for (int i = 0; i < nThreads; i++) {
            es.submit(new Runnable() { public void run() {
                try {
                    barrier.await();
                    for (int i = 0; i < 10000; i++) {
                        for (;;) {
                            try { m.lock(); break; }
                            catch (Throwable t) { checkThrowable(t); }
                        }

                        try { check(! m.tryLock()); }
                        catch (Throwable t) { checkThrowable(t); }

                        try { check(! m.tryLock(1, TimeUnit.MICROSECONDS)); }
                        catch (Throwable t) { checkThrowable(t); }

                        m.unlock();
                    }
                } catch (Throwable t) { unexpected(t); }}});}
        barrier.await();
        es.shutdown();
        check(es.awaitTermination(30, TimeUnit.SECONDS));
    }

    private static class FlakySync extends AbstractQueuedLongSynchronizer {
        private static final long serialVersionUID = -1L;

        public boolean isHeldExclusively() { return getState() == 1; }

        public boolean tryAcquire(long acquires) {
            // Sneak in some tests for queue state
            if (hasQueuedPredecessors())
                check(getFirstQueuedThread() != Thread.currentThread());
            if (getFirstQueuedThread() == Thread.currentThread()) {
                check(hasQueuedThreads());
                check(!hasQueuedPredecessors());
            } else {
                // Might be true, but only transiently
                do {} while (hasQueuedPredecessors() != hasQueuedThreads());
            }

            maybeThrow();
            return compareAndSetState(0, 1);
        }

        public boolean tryRelease(long releases) {
            setState(0);
            return true;
        }

        Condition newCondition() { return new ConditionObject(); }
    }

    private final FlakySync sync = new FlakySync();
    public void lock() { sync.acquire(1); }
    public boolean tryLock() { return sync.tryAcquire(1); }
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }
    public void unlock() { sync.release(1); }
    public Condition newCondition()   { return sync.newCondition(); }
    public boolean isLocked()         { return sync.isHeldExclusively(); }
    public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }

    //--------------------- 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) {if (cond) pass(); else fail();}
    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");}
    @SuppressWarnings("unchecked") static <T extends Throwable>
        void uncheckedThrow(Throwable t) throws T {
        throw (T)t; // rely on vacuous cast
    }
}