java - CyclicBarrier 的可见性同步？

Question

当在 Java 中使用 CyclicBarrier 同步线程时，它们是否同步非 volatile 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
}

我们能否确定线程 1 的 doSomeStuff 调用 b 已设置为 3？尝试时总是 3...

Answer 1

是的，可见性正如您所期望的那样发生，正如您从 CyclicBarrier 类的 javadoc 中看到的那样:

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.