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(* Copyright (C) 2006-2006 Henry Cejtin, Matthew Fluet, Suresh
* Jagannathan, and Stephen Weeks.
*
* MLton is released under a HPND-style license.
* See the file MLton-LICENSE for details.
*)
structure One:
sig
type 'a t
val make: (unit -> 'a) -> 'a t
val use: 'a t * ('a -> 'b) -> 'b
end =
struct
datatype 'a t = T of {more: unit -> 'a,
static: 'a,
staticIsInUse: bool ref}
fun make f = T {more = f,
static = f (),
staticIsInUse = ref false}
fun use (T {more, static, staticIsInUse}, f) =
let
val () = Primitive.MLton.Thread.atomicBegin ()
val b = ! staticIsInUse
val d =
if b then
(Primitive.MLton.Thread.atomicEnd ();
more ())
else
(staticIsInUse := true;
Primitive.MLton.Thread.atomicEnd ();
static)
in
DynamicWind.wind (fn () => f d,
fn () => if b then () else staticIsInUse := false)
end
end
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