(* Title: Pure/Concurrent/synchronized.ML
ID: $Id$
Author: Fabian Immler and Makarius
State variables with synchronized access.
*)
signature SYNCHRONIZED =
sig
type 'a var
val var: string -> 'a -> 'a var
val value: 'a var -> 'a
val timed_access: 'a var -> ('a -> Time.time option) -> ('a -> ('b * 'a) option) -> 'b option
val guarded_access: 'a var -> ('a -> ('b * 'a) option) -> 'b
val change_result: 'a var -> ('a -> 'b * 'a) -> 'b
val change: 'a var -> ('a -> 'a) -> unit
end;
structure Synchronized: SYNCHRONIZED =
struct
(* state variables *)
datatype 'a var = Var of
{name: string,
lock: Mutex.mutex,
cond: ConditionVar.conditionVar,
var: 'a ref};
fun var name x = Var
{name = name,
lock = Mutex.mutex (),
cond = ConditionVar.conditionVar (),
var = ref x};
fun value (Var {name, lock, cond, var}) = SimpleThread.synchronized name lock (fn () => ! var);
(* synchronized access *)
fun timed_access (Var {name, lock, cond, var}) time_limit f =
SimpleThread.synchronized name lock (fn () =>
let
fun try_change () =
let val x = ! var in
(case f x of
SOME (y, x') => (var := x'; SOME y)
| NONE =>
(case time_limit x of
NONE => (ConditionVar.wait (cond, lock); try_change ())
| SOME t =>
if ConditionVar.waitUntil (cond, lock, t) then try_change ()
else NONE))
end;
val res = try_change ();
val _ = ConditionVar.broadcast cond;
in res end);
fun guarded_access var f = the (timed_access var (K NONE) f);
(* unconditional change *)
fun change_result var f = guarded_access var (SOME o f);
fun change var f = change_result var (fn x => ((), f x));
end;