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A coworker and I write software for a variety of platforms running on x86, x64, Itanium, PowerPC, and other 10 year old server CPUs. We just had a discussion about whether mutex functions such as pthread_mutex_lock() ... pthread_mutex_unlock() are sufficient by themselves, or whether the protected variable needs to be volatile. int foo::bar() { //... //code which may or may not access _protected. pthread_mutex_lock(m); int ret = _protected; pthread_mutex_unlock(m); return ret; } My concern is caching. Could the compiler place a copy of _protected on the stack or in a register, and use that stale value in the assignment? If not, what prevents that from happening? Are variations of this pattern vulnerable? I presume that the compiler doesn't actually understand that pthread_mutex_lock() is a special function, so are we just protected by sequence points? Thanks greatly. Update: Alright, I can see a trend with answers explaining why volatile is bad. I respect those answers, but articles on that subject are easy to find online. What I can't find online, and the reason I'm asking this question, is how I'm protected without volatile. If the above code is correct, how is it invulnerable to caching issues?

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