Unsafe

Unsafe 对象提供了非常底层的，操作内存、线程的方法，Unsafe 对象不能直接调用，只能通过反射获得。

public class UnsafeAccessor {
    static Unsafe unsafe;
    static {
        try {
            Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
            theUnsafe.setAccessible(true);
            unsafe = (Unsafe) theUnsafe.get(null);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw new Error(e);
        }
    }
    static Unsafe getUnsafe() {
        return unsafe;
    }
}

Unsafe CAS 操作

public class TestUnsafe {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafe.setAccessible(true);
        Unsafe unsafe = (Unsafe) theUnsafe.get(null);
        System.out.println(unsafe);
        // 1. 获取域的偏移地址
        long idOffset = unsafe.objectFieldOffset(Teacher.class.getDeclaredField("id"));
        long nameOffset = unsafe.objectFieldOffset(Teacher.class.getDeclaredField("name"));
        Teacher t = new Teacher();
        // 2. 执行 cas 操作
        unsafe.compareAndSwapInt(t, idOffset, 0, 1);
        unsafe.compareAndSwapObject(t, nameOffset, null, "张三");
        // 3. 验证
        System.out.println(t);
    }
}
@Data
class Teacher {
    volatile int id;
    volatile String name;
}