Java Unsafe类 CAS简单使用实现自旋锁

自己实现了一个类似AtomicInteger的原子类功能，反复比较并交换，主要用到

• 反射获取Unsafe及对象的静态成员变量
• Unsafe获取地址偏移量
• CAS

public class MyStudy {
    public static int data = 0; 
    public static void main(String[] args) throws Exception{
        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafe.setAccessible(true);
        Unsafe unsafe = (Unsafe) theUnsafe.get(null);
        long dataAddress = unsafe.staticFieldOffset(MyStudy.class.getDeclaredField("data"));
        for (int i = 0; i < 100; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int j = 0; j < 100; j++) {
                        int anInt = unsafe.getInt(MyStudy.class, dataAddress);
                        while(!unsafe.compareAndSwapInt(MyStudy.class,dataAddress,anInt,anInt+1))
                            anInt = unsafe.getInt(MyStudy.class, dataAddress);
                    }
                }
            }).start();
        }
        Thread.sleep(1000);
        System.out.println(data);
    }

}

运行结果10000。

Unsafe类需要使用获取其静态成员变量的方法来拿到，调用getUnsafe()会报错，反射拿取构造函数就违背了Unsafe的初衷（多个Unsafe实例可能会造成线程不安全）。