C&C++中volatile使用场景

    考虑这样一种场景：2个线程共同访问一个全局变量，一个线程只读取它，一个线程只修改它，是否需要对该全局变量加volatile修饰符？

    根据wikipedia的解释wiki/Volatile_(computer_programming)，结论是：不需要。

In C and C++[edit]

In C, and consequently C++, the volatile keyword was intended to^[1]

• allow access to memory mapped devices
• allow uses of variables between setjmp and longjmp
• allow uses of sig_atomic_t variables in signal handlers.

Operations on volatile variables are not atomic, nor do they establish a proper happens-before relationship for threading. This is according to the relevant standards (C, C++, POSIX, WIN32),^[1] and this is the matter of fact for the vast majority of current implementations. Thus, the usage of volatile keyword as a portable synchronization mechanism is discouraged by many C/C++ groups.^[2][3][4]

实际开发中，如果真的有必要我们可以通过gcc -S 查看汇编代码来验证。