The lisp dialects are re-entrant they just don't seem to have a need to call it other than recursion ). W/re the usage of re-entrant as presented here, isn't Scheme's call/cc an example of what is being discussed?  If so, I don't understand why there is an implicit suggestion that re-entrant subrs are directly correlated with thread safety and `concurrency' issues i.e. w/ call/cc the stack is elsewhere thread or no.