2 (* Copyright (C) 2002, HELM Team.
4 * This file is part of HELM, an Hypertextual, Electronic
5 * Library of Mathematics, developed at the Computer Science
6 * Department, University of Bologna, Italy.
8 * HELM is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version 2
11 * of the License, or (at your option) any later version.
13 * HELM is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with HELM; if not, write to the Free Software
20 * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
23 * For details, see the HELM World-Wide-Web page,
24 * http://cs.unibo.it/helm/.
28 let debug_print msg = if debug then prerr_endline msg;;
30 exception Uwobo_failure of string;;
35 val mutex = Mutex.create ()
37 (** condition variable: 'no readers is currently reading' *)
38 val noReaders = Condition.create ()
41 val mutable readersCount = 0
43 method private incrReadersCount = (* internal, not exported *)
44 self#doCritical (lazy (
45 readersCount <- readersCount + 1
48 method private decrReadersCount = (* internal, not exported *)
49 self#doCritical (lazy (
50 if readersCount > 0 then readersCount <- readersCount - 1;
53 method private signalNoReaders = (* internal, not exported *)
54 self#doCritical (lazy (
55 if readersCount = 0 then Condition.signal noReaders
58 method private doCritical: 'a. 'a lazy_t -> 'a =
60 debug_print "<doCritical>";
63 let res = Lazy.force action in
65 debug_print "</doCritical>";
71 method private doReader: 'a. 'a lazy_t -> 'a =
73 debug_print "<doReader>";
75 self#decrReadersCount;
78 self#incrReadersCount;
79 let res = (try Lazy.force action with e -> (cleanup (); raise e)) in
81 debug_print "</doReader>";
84 (* TODO may starve!!!! is what we want or not? *)
85 method private doWriter: 'a. 'a lazy_t -> 'a =
87 debug_print "<doWriter>";
88 self#doCritical (lazy (
89 while readersCount > 0 do
90 Condition.wait noReaders mutex
92 let res = Lazy.force action in
93 debug_print "</doWriter>";