branch for universe

[helm.git] / components / extlib / refCounter.ml

diff --git a/components/extlib/refCounter.ml b/components/extlib/refCounter.ml
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+(* Copyright (C) 2006, 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://helm.cs.unibo.it/
+ *)
+
+type 'a t = ('a, int ref) Hashtbl.t
+
+let create () = Hashtbl.create 113
+
+let incr ~create_cb counters item =
+  try
+    let counter = Hashtbl.find counters item in
+    incr counter
+  with Not_found ->
+    Hashtbl.add counters item (ref 1);
+    create_cb item
+
+let decr ~delete_cb counters item =
+  try
+    let counter = Hashtbl.find counters item in
+    decr counter;
+    if !counter = 0 then begin
+      Hashtbl.remove counters item;
+      delete_cb item
+    end
+  with Not_found ->
+    prerr_endline "RefCounter: attempt to decrease unexistent counter";
+    assert false
+