A file system race is
the condition that occurs
when multiple threads, processes, or computers interleave access and
modification of
the same object within a file system.
Behavior is undefined if calls to functions provided by subclause [filesystems] introduce a file system race.
If the possibility of a file system race would make it unreliable for a
program to test for a precondition before calling a function described herein,
Preconditions: is not specified for the function.