The problem (with get/set/putenv as they are) was isn't the non-use of a mutex. It's the "meaning" of the pointer returned to by getenv(). It returns a char*. Nevermind the persistance of that value - you can work around that by deliberately leaking memory - but it's writeable. Whether it's a good idea to do so ... well. But simply locking "inside" these funcs doesn't solve all the / your issues.