java - Visibility synchronization at CyclicBarrier?

Question

When using a CyclicBarrier for synchronizing threads in Java, do they synchronize non-volatile variables?

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
}

Can we be sure that on Thread 1's doSomeStuff call b has been set to 3? When trying it's always 3...

Answer 1

是的，可见性如您所料发生，正如您从 CyclicBarrier 类的 javadoc 中看到的那样：

内存一致性效果：调用 await() 之前线程中的操作发生在作为屏障操作的一部分的操作之前，而这些操作又在从其他线程中的相应 await() 成功返回之后发生的操作。