It looks like Xcode 5 and above supports C11, but when I try to include stdatomic.h, it says that it cannot find the file? Is it possible to use C11 atomic structures in Xcode?
stdatomic.h is available in Xcode 7 and later.
stdatomic.h
The MacOS 10.12 SDK adds stdatomic.h to its module map, making access also available for the Swift compiler.