Regarding "Any Unix implementation of tmpfile is probably reentrant", that was just a hunch, as I admittedly don't know enough about Unix to say that with confidence. And precisely for this reason I did not say that in the main article. If you see that conversation, I was justifying why I wrote in the article that "GNU tmpfile is reentrant" which is obviously too system-specific. It was precisely because I don't know if other implementations are reentrant, and the only objective thing I can say is that GNU tmpfile is reentrant.