<stdatomic.h> is provided by GCC (not the libc), so I expect it to be available everywhere the atomic builtins are supported. I prefer the builtins. With _Atom

<stdatomic.h> is provided by GCC (not the libc), so I expect it to be available everywhere the atomic builtins are supported. I prefer the builtins. With _Atomic you can easily get seq-cst behavior by mistake, and the <stdatomic.h> interfaces are strictly speaking only valid for _Atomic types.