JDK基于CAS实现原子类盘点解析

public final int getAndIncrement() {
        return unsafe.getAndAddInt(this, valueOffset, 1);
 }

public class AtomicReferenceDemo {
    public static void main(String[] args) {
        User user1 = new User("旭阳");
        // 创建原子引用包装类
        AtomicReference<User> atomicReference = new AtomicReference<>(user1);
        while (true) {
            User user2 = new User("alvin");
            // 比较并交换
            if (atomicReference.compareAndSet(user1, user2)) {
                break;
            }
        }
        System.out.println(atomicReference.get());
    }
}
@Data
@AllArgsConstructor
@ToString
class User {
    private String name;
}

@Slf4j(topic = "a.AtomicStampedReferenceTest")
public class AtomicStampedReferenceTest {
    // 构造AtomicStampedReference
    static AtomicStampedReference<String> ref = new AtomicStampedReference<>("A", 0);
    public static void main(String[] args) throws InterruptedException {
        log.debug("main start...");
        // 获取值 A
        String prev = ref.getReference();
        // 获取版本号
        int stamp = ref.getStamp();
        log.debug("版本 {}", stamp);
        // 如果中间有其它线程干扰，发生了 ABA 现象
        other();
        Thread.sleep(1000);
        // 尝试改为 C
        log.debug("change A->C {}", ref.compareAndSet(prev, "C", stamp, stamp + 1));
    }
    private static void other() throws InterruptedException {
        new Thread(() -> {
            log.debug("change A->B {}", ref.compareAndSet(ref.getReference(), "B",
                    ref.getStamp(), ref.getStamp() + 1));
            log.debug("更新版本为 {}", ref.getStamp());
        }, "t1").start();
        Thread.sleep(500);
        new Thread(() -> {
            log.debug("change B->A {}", ref.compareAndSet(ref.getReference(), "A",
                    ref.getStamp(), ref.getStamp() + 1));
            log.debug("更新版本为 {}", ref.getStamp());
        }, "t2").start();
    }
}

@Slf4j(topic = "c.AtomicMarkableReferenceTest")
public class AtomicMarkableReferenceTest {
    // 构造 AtomicMarkableReference, 初始标记为false
    static AtomicMarkableReference<String> ref = new AtomicMarkableReference<>("A", false);
    public static void main(String[] args) throws InterruptedException {
        log.debug("main start...");
        other();
        Thread.sleep(1000);
        // 看看是否发生了变化
        log.debug("change {}", ref.isMarked());
    }
    private static void other() throws InterruptedException {
        new Thread(() -> {
            log.debug("change A->B {}", ref.compareAndSet(ref.getReference(), "B",
                    false, true));
        }, "t1").start();
        Thread.sleep(500);
        new Thread(() -> {
            log.debug("change B->A {}", ref.compareAndSet(ref.getReference(), "A",
                    true, true));
        }, "t2").start();
    }
}

public class AtomicIntegerArrayTest {
    public static void main(String[] args) throws Exception{
        AtomicIntegerArray array = new AtomicIntegerArray(10);
        Thread t1 = new Thread(()->{
            int index;
            for(int i=1; i<100000; i++) {
                index = i%10; //范围0~9
                array.incrementAndGet(index);
            }
        });
        Thread t2 = new Thread(()->{
            int index;
            for(int i=1; i<100000; i++) {
                index = i%10; //范围0~9
                array.decrementAndGet(index);
            }
        });
        t1.start();
        t2.start();
        Thread.sleep(5 * 1000);
        System.out.println(array.toString());
    }
}

@Data
public class AtomicReferenceFieldUpdaterTest {
    private volatile int age = 10;
    private int age2;
    public static void main(String[] args) {
        AtomicIntegerFieldUpdater integerFieldUpdater = AtomicIntegerFieldUpdater.newUpdater(AtomicReferenceFieldUpdaterTest.class, "age");
        AtomicReferenceFieldUpdaterTest ref = new AtomicReferenceFieldUpdaterTest();
        // 对volatile 的age字段+1
        integerFieldUpdater.getAndIncrement(ref);
        System.out.println(ref.getAge());
        // 修改 非volatile的age2
        integerFieldUpdater = AtomicIntegerFieldUpdater.newUpdater(AtomicReferenceFieldUpdaterTest.class, "age2");
        integerFieldUpdater.getAndIncrement(ref);
    }
}

public class LongAdderTest {
    public static void main(String[] args) {
        System.out.println("LongAdder ...........");
        for (int i = 0; i < 5; i++) {
            addFunc(() -> new LongAdder(), adder -> adder.increment());
        }
        System.out.println("AtomicLong ...........");
        for (int i = 0; i < 5; i++) {
            addFunc(() -> new AtomicLong(), adder -> adder.getAndIncrement());
        }
    }
    private static <T> void addFunc(Supplier<T> adderSupplier, Consumer<T> action) {
        T adder = adderSupplier.get();
        long start = System.nanoTime();
        List<Thread> ts = new ArrayList<>();
        // 40个线程，每人累加 50 万
        for (int i = 0; i < 40; i++) {
            ts.add(new Thread(() -> {
                for (int j = 0; j < 500000; j++) {
                    action.accept(adder);
                }
            }));
        }
        ts.forEach(t -> t.start());
        ts.forEach(t -> {
            try {
                t.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        long end = System.nanoTime();
        System.out.println(adder + " cost:" + (end - start)/1000_000);
    }
}