snapshot Wed, 27 Nov 2002 18:10:57 +0100

[helm.git] / helm / uwobo / src / ocaml / uwobo_common.ml

diff --git a/helm/uwobo/src/ocaml/uwobo_common.ml b/helm/uwobo/src/ocaml/uwobo_common.ml
new file mode 100644 (file)
index 0000000..09f9ba5
--- /dev/null
+++ b/helm/uwobo/src/ocaml/uwobo_common.ml
@@ -0,0 +1,98 @@
+
+(* Copyright (C) 2002, HELM Team.
+ * 
+ * This file is part of HELM, an Hypertextual, Electronic
+ * Library of Mathematics, developed at the Computer Science
+ * Department, University of Bologna, Italy.
+ * 
+ * HELM is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * 
+ * HELM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HELM; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA  02111-1307, USA.
+ * 
+ * For details, see the HELM World-Wide-Web page,
+ * http://cs.unibo.it/helm/.
+ *)
+
+let debug = false;;
+let debug_print msg = if debug then prerr_endline msg;;
+
+exception Uwobo_failure of string;;
+
+class threadSafe =
+  object (self)
+
+    val mutex = Mutex.create ()
+
+      (** condition variable: 'no readers is currently reading' *)
+    val noReaders = Condition.create ()
+
+      (** readers count *)
+    val mutable readersCount = 0
+
+    method private incrReadersCount = (* internal, not exported *)
+      self#doCritical (lazy (
+        readersCount <- readersCount + 1
+      ))
+
+    method private decrReadersCount = (* internal, not exported *)
+      self#doCritical (lazy (
+        if readersCount > 0 then readersCount <- readersCount - 1;
+      ))
+
+    method private signalNoReaders =  (* internal, not exported *)
+      self#doCritical (lazy (
+        if readersCount = 0 then Condition.signal noReaders
+      ))
+
+    method private doCritical: 'a. 'a lazy_t -> 'a =
+      fun action ->
+        debug_print "<doCritical>";
+        (try
+          Mutex.lock mutex;
+          let res = Lazy.force action in
+          Mutex.unlock mutex;
+          debug_print "</doCritical>";
+          res
+        with e ->
+          Mutex.unlock mutex;
+          raise e);
+
+    method private doReader: 'a. 'a lazy_t -> 'a =
+      fun action ->
+        debug_print "<doReader>";
+        let cleanup () =
+          self#decrReadersCount;
+          self#signalNoReaders
+        in
+        self#incrReadersCount;
+        let res = (try Lazy.force action with e -> (cleanup (); raise e)) in
+        cleanup ();
+        debug_print "</doReader>";
+        res
+
+      (* TODO may starve!!!! is what we want or not? *)
+    method private doWriter: 'a. 'a lazy_t -> 'a =
+      fun action ->
+        debug_print "<doWriter>";
+        self#doCritical (lazy (
+          while readersCount > 0 do
+            Condition.wait noReaders mutex
+          done;
+          let res = Lazy.force action in
+          debug_print "</doWriter>";
+          res
+        ))
+
+  end
+