参考类型的易失性 - 它总是避免由于JMM发布参考问题？

本文介绍了参考类型的易失性 - 它总是避免由于JMM发布参考问题？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 假设这个类： public class AmIThreadSafe { private int a; private int b; AmIThreadSafe（int a，int b）{ this.a = a; this.b = b; } } 假设实例引用此类（声明为此（引用）转义时，某些线程可以访问（导致竞争条件）：code> volatile p> volatile AmIThreadSafe instance = new AmIThreadSafe（1,2）; 在这里，我确定分配实例 但是关于 AmIThreadSafe的 c> fields？ 外部 volatile 关键字也意味着发生之前关系 a 和 b 字段？ 或者是可能的任何线程看到过时的值（默认值 0 在这种情况下，因为 int ） 换句话说，我应该声明 a b final 或 volatile 或者只是在实例的引用上指示 volatile ？ 更新后 - 好的答案： ---------------------------- 以下文章通过其样例证实了在我的情况下， a 和 b 受到JMM优化的保护，防止永久 发生之前 关系。 http://jeremymanson.blogspot.fr/2008/11/what-volatile-means-in-java.html 解决方案将实例声明为 volatile 不会使其字段 volatile ，但如果我正确理解你的问题，然后—是的，在你的情况下就够了。 每§ 17.4.5的规范： a volatile 写入一个线程 happens-before 任何后续 volatile 线程。 同一个线程中的语句具有您期望的 happens-before 关系。 > 关系是可传递的。 因此，如果线程感知到 code>作为已经初始化，然后实例 发生之前的的初始化，以及实例的字段 happens-before ，因此线程会将实例的字段视为已初始化。 Assuming this class:public class AmIThreadSafe { private int a; private int b; AmIThreadSafe(int a, int b) { this.a = a; this.b = b; }}Assuming that instance's reference to this class (declared as volatile) is accessible by some threads (leading to race condition) as soon as the this(reference) escapes:volatile AmIThreadSafe instance = new AmIThreadSafe(1,2);Here, I'm sure that the fact of assigning instance reference happens-before reading by threads.But what about the AmIThreadSafe's fields? Does the external volatile keyword also imply an happens-before relation concerning a and b fields? Or is it rather possible to end up with any thread seeing stale values (default values 0 in this case since int) due to a potential statements reordering during constructor?In other word, should I declare a and b final or volatile to prevent any surprises with the JMM or is just indicating volatile on the instance's reference enough?----------------UPDATED POST - A GOOD ANSWER:----------------------------The following article confirms by its sample that in my case, a and b are protected from JMM optimisations that prevent a permanent happens-before relation. http://jeremymanson.blogspot.fr/2008/11/what-volatile-means-in-java.html 解决方案 Declaring instance as volatile does not make its fields volatile, but if I understand your question correctly, then — yes, it's enough in your case.Per §17.4.5 of the spec:a volatile write in one thread happens-before any subsequent volatile read in another thread.statements within the same thread have the happens-before relationship that you'd expect.happens-before relationships are transitive.So, if a thread perceives instance as having been initialized, then the initialization of instance happened-before it, and the initialization of instance's fields happened-before that, so the thread will perceive instance's fields as having been initialized. 这篇关于参考类型的易失性 - 它总是避免由于JMM发布参考问题？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！