Java中的易失性变量 [英] Volatile variable in Java

问题描述

因此，我正在阅读这本名为 Java Concurrency in Practice 的书，我坚持这一个解释，我没有一个例子似乎不能理解。这是引号：

So I am reading this book titled Java Concurrency in Practice and I am stuck on this one explanation which I cannot seem to comprehend without an example. This is the quote:

当线程 A 写入volatile
变量，随后线程 B
读取同一变量，
可见的所有变量的值
变量之前，可以看到< code> B >

When thread A writes to a volatile variable and subsequently thread B reads that same variable, the values of all variables that were visible to A prior to writing to the volatile variable become visible to B after reading the volatile variable.

有人可以给我一个反例，为什么 A B 变量可见的写入变量变量

Can someone give me a counterexample of why "the values of ALL variables that were visible to A prior to writing to the volatile variable become visible to B AFTER reading the volatile variable"?

困惑为什么所有其他非易失性变量在读取volatile变量之前不会变为可见 B ？

I am confused why all other non-volatile variables do not become visible to B before reading the volatile variable?

推荐答案

线程B可以有这些变量的CPU本地缓存。读取volatile变量可确保任何中间高速缓存从以前写入volatile到flush。

Thread B may have a CPU-local cache of those variables. A read of a volatile variable ensures that any intermediate cache flush from a previous write to the volatile is observed.

有关示例，请阅读以下链接，使用Volatile修复双重检查锁定：

For an example, read the following link, which concludes with "Fixing Double-Checked Locking using Volatile":

http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html

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