在与中断线程的关系之前，是否在线程上调用interrupt（） [英] Does calling interrupt() on a thread create happens-before relation with the interrupted thread

问题描述

换句话说，我想知道在中断线程中检测到中断时，在中断之前更改变量是否始终可见。例如，

In other words I want to know if changing variable before interrupt is always visible when interrupt is detected inside interrupted thread. E.g.

private int sharedVariable;

public static void interruptTest() {
    Thread someThread = new Thread(() -> {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            // Is it here guaranteed that changes before interrupt are always visible here?
            System.out.println(sharedVariable);
        }
    });
    someThread.start();
    Thread.sleep(1000);
    sharedVariable = 10;
    someThread.interrupt();
}

我试图在 Java语言规范和
java.util.concurrent包的摘要页面在 Java教程中提到但是中断没有被提及。

I tried to find answer in Java language specification and in Summary page of the java.util.concurrent package mentioned in Java tutorial but interrupt was not mentioned.

我知道 volatile 和其他同步原语但是我需要它们吗？

I know about volatile and other synchronize primitives but do I need them?

推荐答案

是的，从线程T1中断线程T2会产生发生之前 T1和T2之间的关系，如 JLS 17.4.4。同步订单：

Yes, interrupting a thread T2 from a thread T1 creates a happens-before relationship between T1 and T2, as described in the JLS 17.4.4. Synchronization Order:

如果线程T1中断线程T2，则T1
的中断与任何点同步任何其他线程（包括T2）
确定T2已被中断（通过抛出
InterruptedException或通过调用Thread.interrupted或
Thread.isInterrupted）。

If thread T1 interrupts thread T2, the interrupt by T1 synchronizes-with any point where any other thread (including T2) determines that T2 has been interrupted (by having an InterruptedException thrown or by invoking Thread.interrupted or Thread.isInterrupted).

现在这只暗示T1 同步 - 检测到中断T2，而你问及发生在之前的。幸运的是，前者暗示后者来自 17.4.5。发生在订单之前：

Now that only implies that T1 synchronizes-with the detection of the interrupt T2, while you asked about happens-before. Luckily the former implies the latter from 17.4.5. Happens-before Order:

可以通过before-before关系订购两个操作。如果一个
的操作发生在另一个之前，那么第一个是可见的，而
在第二个之前订购。

Two actions can be ordered by a happens-before relationship. If one action happens-before another, then the first is visible to and ordered before the second.

如果我们有两个动作x和y，我们写hb（x，y）表示x
发生在y之前。

If we have two actions x and y, we write hb(x, y) to indicate that x happens-before y.

• ...


• 如果动作x与后续动作y同步，那么我们也有hb（x，y）。

因此，您可以安全地访问 sharedVariable 知道它具有（至少）T1写入的值，即使没有 volatile 。

So you are safe to access sharedVariable knowing that it has (at least) the value written by T1, even without volatile.

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