[PaulDavisThe1st]

Reasoning about null ptr, use after free, buffer overflows is tricky, because you cannot determine whether you've done the right thing by "just reading the code".

If you are doing multithreaded programming, and there's a variable shared among threads, and there's a read or write of the variable without a mutex in sight, you've done it wrong.

Yes, the mutex owner could be a caller several layers up the stack. Sometimes that's a legitimate design, and if you know what you're doing your function/method names will reflect the fact that the lock is already held. If you don't know what you're doing, you should avoid that design and lock the mutex in the same scope as the read/write.

And of course, using RAII with C++ (or anything else that supports it) makes this sort of thing easy to do.