java - volatile 和原子之间的区别

Question

int value = 0;
volatile boolean done = false;

// Thread A:
value = 1; done = true;

// Thread B:
if (done) System.out.println(value);

很好，因为完成被定义为 volatile 。

关于相同的代码，除了将done定义为AtomicBoolean之外，它将实现相同的效果吗？换句话说，除了原子操作和可见操作以外，原子操作(RMW)是否还可以确保所有先前的写入都刷新到共享内存中？

int value = 0;
AtomicBoolean done = new AtomicBoolean(false);

// Thread A:
value = 1; done.set(true);

// Thread B:
if (done.get()) System.out.println(value);

Answer 1

From the Javadoc of java.util.concurrent :

The memory effects for accesses and updates of atomics generally follow the rules for volatiles, as stated in The Java Language Specification (17.4 Memory Model):

• get has the memory effects of reading a volatile variable.
• set has the memory effects of writing (assigning) a volatile variable.
• ...

因此，在这种情况下， volatile和 AtomicBoolean之间没有区别。