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CoDeleven avatar CoDeleven commented on June 11, 2024

可以保证。可以从两个方面理解：
内存屏障：
volatile关键字会在volatile写之前插入StoreStore，保证volatile写之前的内容先写入主内存，保证对所有线程可见（禁止a写和flag写的重排序）；而volatile读后会插入LoadLoad和LoadStore，保证在读取变量a前，先读取flag（禁止a读和flag读重排序）。所以就能保证它们的可见性。

happens-before：
作者的代码没看，你可以看我的理解一下 /捂脸
image

最后根据传递性规则，① happens-before ④

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MikasaLee avatar MikasaLee commented on June 11, 2024

懂了，谢谢老哥指点

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MikasaLee avatar MikasaLee commented on June 11, 2024

老哥还想在问一下细节
JMM的内存屏障只是用来确保对volatile对象的读写操作不会发生重排序。
但是真正volatile关键字真正用来同步线程内存和主内存的操作是原文说的"Lock前缀的指令"这个作用吧，这个理解对么？
（顺便问一下为啥我javap 看指令操作时没有发现一个Lock开头的指令。。）

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CoDeleven avatar CoDeleven commented on June 11, 2024

lock开头的指令是在JIT的汇编代码里
参考周志明的《深入Java虚拟机》P111

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