|The stupid question is the question not asked|
What do you mean by "thread-safe"?
If two threads attempt to touch the same file, first one will succeed(*), and then the other will succeed(*).
Of course, it will be impossible to know which thread succeeded first (or last), but the files timestamps will have changed.
And whichever order they do it in, the file will have been touched twice as programmed.
How do you want to define "not thread-safe"?
(*)Where "success" is defined as altering the timestamps on the file to some value.
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