java.util.concurrent.atomic.AtomicStampedReference#compareAndSet()源码实例Demo

/**
 * compareAndSet in one thread enables another waiting for reference value
 * to succeed
 */
public void testCompareAndSetInMultipleThreads() throws Exception {
    final AtomicStampedReference ai = new AtomicStampedReference(one, 0);
    Thread t = new Thread(new CheckedRunnable() {
        public void realRun() {
            while (!ai.compareAndSet(two, three, 0, 0))
                Thread.yield();
        }});

    t.start();
    assertTrue(ai.compareAndSet(one, two, 0, 0));
    t.join(LONG_DELAY_MS);
    assertFalse(t.isAlive());
    assertSame(three, ai.getReference());
    assertEquals(0, ai.getStamp());
}
 

/**
 * compareAndSet in one thread enables another waiting for stamp value
 * to succeed
 */
public void testCompareAndSetInMultipleThreads2() throws Exception {
    final AtomicStampedReference ai = new AtomicStampedReference(one, 0);
    Thread t = new Thread(new CheckedRunnable() {
        public void realRun() {
            while (!ai.compareAndSet(one, one, 1, 2))
                Thread.yield();
        }});

    t.start();
    assertTrue(ai.compareAndSet(one, one, 0, 1));
    t.join(LONG_DELAY_MS);
    assertFalse(t.isAlive());
    assertSame(one, ai.getReference());
    assertEquals(2, ai.getStamp());
}
 

/**
 * compareAndSet in one thread enables another waiting for reference value
 * to succeed
 */
public void testCompareAndSetInMultipleThreads() throws Exception {
    final AtomicStampedReference ai = new AtomicStampedReference(one, 0);
    Thread t = new Thread(new CheckedRunnable() {
        public void realRun() {
            while (!ai.compareAndSet(two, three, 0, 0))
                Thread.yield();
        }});

    t.start();
    assertTrue(ai.compareAndSet(one, two, 0, 0));
    t.join(LONG_DELAY_MS);
    assertFalse(t.isAlive());
    assertSame(three, ai.getReference());
    assertEquals(0, ai.getStamp());
}
 

/**
 * compareAndSet in one thread enables another waiting for stamp value
 * to succeed
 */
public void testCompareAndSetInMultipleThreads2() throws Exception {
    final AtomicStampedReference ai = new AtomicStampedReference(one, 0);
    Thread t = new Thread(new CheckedRunnable() {
        public void realRun() {
            while (!ai.compareAndSet(one, one, 1, 2))
                Thread.yield();
        }});

    t.start();
    assertTrue(ai.compareAndSet(one, one, 0, 1));
    t.join(LONG_DELAY_MS);
    assertFalse(t.isAlive());
    assertSame(one, ai.getReference());
    assertEquals(2, ai.getStamp());
}
 

public Object setReloadRequired() {
    if (!reloadSupported) {
        return setRestartRequired();
    }
    AtomicStampedReference<State> stateRef = state;
    int newStamp = stamp.incrementAndGet();
    int[] receiver = new int[1];
    // Keep trying until stateRef is RELOAD_REQUIRED with our stamp
    for (;;) {
        State was = stateRef.get(receiver);
        if (was == State.STARTING || was == State.STOPPING || was == State.RESTART_REQUIRED) {
            break;
        }
        synchronized (service) {
            if (stateRef.compareAndSet(was, State.RELOAD_REQUIRED, receiver[0], newStamp)) {
                service.stateChanged(State.RELOAD_REQUIRED);
                break;
            }
        }
    }
    return Integer.valueOf(newStamp);
}
 

public Object setRestartRequired() {
    AtomicStampedReference<State> stateRef = state;
    int newStamp = stamp.incrementAndGet();
    int[] receiver = new int[1];
    // Keep trying until stateRef is RESTART_REQUIRED with our stamp
    for (;;) {
        State was = stateRef.get(receiver);
        if (was == State.STARTING || was == State.STOPPING) {
            break;
        }
        synchronized (service) {
            if (stateRef.compareAndSet(was, State.RESTART_REQUIRED, receiver[0], newStamp)) {
                restartRequiredFlag = true;
                service.stateChanged(State.RESTART_REQUIRED);
                break;
            }
        }
    }
    return Integer.valueOf(newStamp);
}
 

public static void main(String[] args) throws InterruptedException {
    // 共享锁演示
    final MyReadWriteLock rwLock = new MyReadWriteLock();
    // 创建读锁 r1 和 r2
    Thread r1 = new Thread(new Runnable() {
        @Override
        public void run() {
            rwLock.read();
        }
    }, "r1");
    Thread r2 = new Thread(new Runnable() {
        @Override
        public void run() {
            rwLock.read();
        }
    }, "r2");
    r1.start();
    r2.start();
    // 等待同时读取线程执行完成
    r1.join();
    r2.join();
    // 开启写锁的操作
    new Thread(new Runnable() {
        @Override
        public void run() {
            rwLock.write();
        }
    }, "w1").start();
    new Thread(new Runnable() {
        @Override
        public void run() {
            rwLock.write();
        }
    }, "w2").start();
    // AtomicStampedReference（解决 ABA 问题）使用演示
    String name = "老王";
    String newName = "Java";
    AtomicStampedReference<String> as = new AtomicStampedReference<String>(name, 1);
    System.out.println("值：" + as.getReference() + " | Stamp：" + as.getStamp());
    as.compareAndSet(name, newName, as.getStamp(), as.getStamp() + 1);
    System.out.println("值：" + as.getReference() + " | Stamp：" + as.getStamp());
}