我是否需要同步对中断方法的调用？ [英] Do I need to synchronize a call to the interrupt method?

问题描述

在 Java SE 7 中查询JavaDocs和 Thread.interrupt（）方法的源代码这个：

Consulting the JavaDocs and the source code of the Thread.interrupt() method in Java SE 7 I found this:

public void interrupt() {
    if (this != Thread.currentThread())
        checkAccess();

    synchronized (blockerLock) {
        Interruptible b = blocker;
        if (b != null) {
            interrupt0();           // Just to set the interrupt flag
            b.interrupt(this);
            return;
        }
    }
    interrupt0(); //1, Outside of the synchronized block
}

//...

private native void interrupt0();

可以看出， // 1的本机方法调用在同步块之外。那么，如果不将 interrupt（）方法调用到 synchronized 块中，是否安全？

As can be seen, the native method invocation at //1 is outside of the synchronized block. So, is it safe if don't put a call to the interrupt() method into a synchronized block?

Thread t;
//something else
t.interrupt(); //Not in a synchronized block

它是否是线程安全的？如果超过1个线程试图同时中断它怎么办？原生方法 interrupt0 将如何表现呢？

Will it be thread-safe? What if more than 1 thread will try to interrupt it simultaneously? How will the native method interrupt0 behave then?

推荐答案

我会说是的...它是线程安全的。

I would say yes ... it is thread-safe.

理由：

1. 如果应用程序需要在 synchronized 块中调用 interrupt（），那么规范（ javadoc）会这样说，并且还说出需要同步的对象以获得线程安全性。实际上，javadoc对此没有任何说明。

1. If it was necessary for applications to call interrupt() in a synchronized block, then the the spec (the javadoc) would say so, and also say what object you needed to synchronize on to get thread-safety. In fact, the javadoc says nothing about this.

如果应用程序需要调用 interrupt（）在 synchronized 块中，然后Oracle Java Tutorial on Concurrency会提到它在此页。它没有。

If it was necessary for applications to call interrupt() in a synchronized block, then the Oracle Java Tutorial on Concurrency would mention it on this page. It doesn't.

如果需要在 Thread 对象上进行外部同步才能使 interrupt（）调用线程安全，然后很难解释为什么该方法也在进行内部同步。 （如果有必要，他们可以/将会使整个方法同步。）

If external synchronization on the Thread object was necessary to make the interrupt() call thread-safe, then it is hard to explain why the method is doing internal synchronization as well. (They could / would have made the entire method synchronized if it was necessary.)

上述证据是（IMO）虽然不是绝对的证据，但令人信服。如果你想证明 interrupt（）是线程安全的，你可以通过彻底分析 interrupt0（）<的本机代码实现来获得它。 / code>。我没有查看本机代码，但我希望 interrupt0 在内部是线程安全的，这足以使中断方法线程安全。

The above evidence is (IMO) convincing, though not absolute proof. If you wanted proof that interrupt() is thread-safe, you would get it by a thorough analysis of the native code implementation for interrupt0(). I haven't looked at the native code, but I would expect that interrupt0 is internally thread-safe, and that that is sufficient to make the interrupt method thread-safe.

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