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Java并发编程：volatile关键字解析

发布时间：2020-12-14 06:38:17 所属栏目：Java 来源：网络整理
导读：转自： p style="border:0px; margin-top:0px; margin-bottom:20px; padding-top:0px; padding-bottom:0px; font-size:14px; font-family:'Microsoft YaHei',宋体,'Myriad Pro',Lato,'Helvetica Neue',Helvetica,Arial,sans-serif" volatile这个关键字可能很

转自：

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volatile这个关键字可能很多朋友都听说过，或许也都用过。在Java 5之前，它是一个备受争议的关键字，因为在程序中使用它往往会导致出人意料的结果。在Java 5之后，volatile关键字才得以重获生机。


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volatile关键字虽然从字面上理解起来比较简单，但是要用好不是一件容易的事情。由于volatile关键字是与Java的内存模型有关的，因此在讲述volatile关键之前，我们先来了解一下与内存模型相关的概念和知识，然后分析了volatile关键字的实现原理，最后给出了几个使用volatile关键字的场景。


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以下是本文的目录大纲：


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一.内存模型的相关概念


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二.并发编程中的三个概念


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三.Java内存模型


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四..深入剖析volatile关键字


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五.使用volatile关键字的场景


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若有不正之处请多多谅解，并欢迎批评指正。


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请尊重作者劳动成果，转载请标明原文链接：


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http://www.cnblogs.com/dolphin0520/p/3920373.html


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一.内存模型的相关概念
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大家都知道，计算机在执行程序时，每条指令都是在CPU中执行的，而执行指令过程中，势必涉及到数据的读取和写入。由于程序运行过程中的临时数据是存放在主存（物理内存）当中的，这时就存在一个问题，由于CPU执行速度很快，而从内存读取数据和向内存写入数据的过程跟CPU执行指令的速度比起来要慢的多，因此如果任何时候对数据的操作都要通过和内存的交互来进行，会大大降低指令执行的速度。因此在CPU里面就有了高速缓存。


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也就是，当程序在运行过程中，会将运算需要的数据从主存复制一份到CPU的高速缓存当中，那么CPU进行计算时就可以直接从它的高速缓存读取数据和向其中写入数据，当运算结束之后，再将高速缓存中的数据刷新到主存当中。举个简单的例子，比如下面的这段代码：


<div style="border:0px; margin:0px; padding:0px; font-size:14px; font-family:'Microsoft YaHei',sans-serif">
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<table border="0" cellpadding="0" cellspacing="0" style="border-collapse:collapse; border-spacing:0px; border:0px!important; margin:0px!important; padding:0px!important; font-size:12px!important; width:100%!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; min-height:inherit!important"><tbody style="border:0px!important; margin:0px!important; padding:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important"><tr style="border:0px!important; margin:0px!important; padding:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important">
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1
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<div class="container" style="border:0px!important; margin:0px!important; padding:0px!important; width:auto!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:relative!important; right:auto!important; top:auto!important; vertical-align:baseline!important; min-height:inherit!important">
<div class="line number1 index0 alt2" style="border:0px!important; margin:0px!important; padding:0px 1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important; white-space:pre!important">
<code class="java plain" style="border:0px!important; margin:0px!important; padding:0px!important; font-family:Consolas,monospace!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important">i
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