volatile 和 atomic 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);

这很好，因为 done 被定义为易变的。

除了将 done 定义为 AtomicBoolean 之外，相同的代码怎么样 - 它是否实现了相同的效果？换句话说，原子（RMW）操作除了是原子的和可见的之外，还保证所有先前的写入都刷新到共享内存吗？

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.

...

所以在这种情况下，volatile和AtomicBoolean没有区别。

volatile 和 atomic 之间的区别

Differences between volatile and atomic

java

multithreading

atomic

volatile