走入UnSafe

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

@Data
class Student {
 	volatile int id;
 	volatile String name;
}

Unsafe unsafe = UnsafeAccessor.getUnsafe();
Field id = Student.class.getDeclaredField("id");
Field name = Student.class.getDeclaredField("name");
// 获得成员变量的偏移量
long idOffset = UnsafeAccessor.unsafe.objectFieldOffset(id);
long nameOffset = UnsafeAccessor.unsafe.objectFieldOffset(name);
Student student = new Student();
// 使用 cas 方法替换成员变量的值
UnsafeAccessor.unsafe.compareAndSwapInt(student, idOffset, 0, 20); // 返回 true
UnsafeAccessor.unsafe.compareAndSwapObject(student, nameOffset, null, "张三"); // 返回 true
System.out.println(student);

输出：

Student(id=20, name=张三)