It's not overly difficult to guarantee, the UNIX/Linux kernel does it just fine. It does require more work in that the libc file cache will need to invalidate i

It's not overly difficult to guarantee, the UNIX/Linux kernel does it just fine. It does require more work in that the libc file cache will need to invalidate itself if the source file / socket changes state (either via atime if the filesystem supports it or via inotify/fnotify). Obviously invalidating the cache will lead to lower performance but more correct behaviour.