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使用了互斥量访问全局变量还需要 volatile 吗

tk posted @ Jun 25, 2012 07:43:50 PM in C with tags pthread , 2337 阅读

今天在看 pthread ,pthread_cond_wait 是个很有趣的函数,至于标题所提出的问题也是困扰我很久的一个“小问题”。

因为“虽然”互斥量能保证多个线程访问全局变量的一致性,但是由于编译器优化和 cache 机制,多个线程对于内存中变量操作也许就没有“真正”反馈到内存里(也许仅仅改变了寄存器中的缓存值),但是这个说法又与互斥量的目的有矛盾(既然都要保证一致性,为什么又“出现”这种内存中“不一致”的状况?)

于是就找资料,终于找到一个很完备的解释:多处理器环境和线程同步的高级话题(白杨) 涉及到 内存屏障 (memory barrier)技术。

至于 pthread_cond_wait 和 pthread_cond_t 的使用,也是有很多需要理解和注意的细节,在这里可以解惑:
http://www.cppblog.com/izualzhy/archive/2011/11/14/160120.html

pthread 的使用教程这里有:http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html

不过都是英文,可能在一些细节解释上理解会有难度,不过有搜索引擎还是很容易的,另外也可以参考 《Unix 高级环境编程》也就是所谓的“APUE”。

越来越喜欢 C 的风格和思想了,算是回归吧。

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