For the functions here:

#include <libkern/OSAtomic.h>

there are OSAtomic and OSAtomicBarrier versions.

However, the documentation does not show sample code for:

1. When is it safe to use just OSAtomic, without the OSAtomicBarrier version
2. When is it that OSAtomic would be unsafe, but OSAtomiBarrier would be safe.

Can anyone provide explainations + sample codes?

[Random ramblings of "your opinion" without actual code is useless. Readers: please down vote such answers; and vigrously upvote answers with actual code.]

[C/C++ code preferred; Assembly okay too.]