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7f918cf1 CE |
1 | (* Copyright (C) 2006-2006 Henry Cejtin, Matthew Fluet, Suresh |
2 | * Jagannathan, and Stephen Weeks. | |
3 | * | |
4 | * MLton is released under a BSD-style license. | |
5 | * See the file MLton-LICENSE for details. | |
6 | *) | |
7 | ||
8 | structure One: | |
9 | sig | |
10 | type 'a t | |
11 | ||
12 | val make: (unit -> 'a) -> 'a t | |
13 | val use: 'a t * ('a -> 'b) -> 'b | |
14 | end = | |
15 | struct | |
16 | datatype 'a t = T of {more: unit -> 'a, | |
17 | static: 'a, | |
18 | staticIsInUse: bool ref} | |
19 | ||
20 | fun make f = T {more = f, | |
21 | static = f (), | |
22 | staticIsInUse = ref false} | |
23 | ||
24 | fun use (T {more, static, staticIsInUse}, f) = | |
25 | let | |
26 | val () = Primitive.MLton.Thread.atomicBegin () | |
27 | val b = ! staticIsInUse | |
28 | val d = | |
29 | if b then | |
30 | (Primitive.MLton.Thread.atomicEnd (); | |
31 | more ()) | |
32 | else | |
33 | (staticIsInUse := true; | |
34 | Primitive.MLton.Thread.atomicEnd (); | |
35 | static) | |
36 | in | |
37 | DynamicWind.wind (fn () => f d, | |
38 | fn () => if b then () else staticIsInUse := false) | |
39 | end | |
40 | end |