CyclicBarrier上的java可见性同步？

Question

在Java中使用CyclicBarrier同步线程时，它们是否同步非易失性变量

int a = 0;
int b = 0;
CyclicBarrier barrier = new CyclicBarrier(2);

/*** Thread 1 ***/
public void run() {
    a = 2;
    barrier.await();

    doSomeStuff(b); // no side-effects
}

/*** Thread 2 ***/
public void run() {
    b = 3;
    barrier.await();

    doSomeStuff(a); // no side-effects
}

我们可以确定线程1的doSomeStuff调用b已设置为3吗？ 尝试时总是3

Answer 1

是的，正如您从CyclicBarrier类的javadoc中所看到的，可视性正如您所期望的那样：

Memory consistency effects: Actions in a thread prior to calling await() happen-before actions that are part of the barrier action, which in turn happen-before actions following a successful return from the corresponding await() in other threads.