使用了互斥量访问全局变量还需要 volatile 吗
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。
Sep 14, 2022 01:14:11 PM
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