[MLton] Int.fmt thread unsafe? (YUCK)

[Henry Cejtin]

By  putting  the  conditional  call  to  more  inside  the  wind you have the
advantage that the critical region is smaller (it does not include more), but
the disadvantage that you have to test b again.

One can eliminate all but one test using the following (rather ugly) code:

    fun use (T {more, static, staticIsInUse}, f) =
           (Primitive.Thread.atomicBegin ()
            ; if ! staticIsInUse
                 then (Primitive.Thread.atomicEnd ()
                       ; f (more ()))
                 else (staticIsInUse := true
                       ; Primitive.Thread.atomicEnd ()
                       ; DynamicWind.wind (fn () => f static,
                                           fn () => staticIsInUse := false)))

Note,   the  code  for  f  is  now  called  in  two  places  (with  different
continuations) and that might change inlining.