>From 641a075ed3bb077731f0971048c807f350caba2c Mon Sep 17 00:00:00 2001
From: Matt Lilley <address@hidden>
Date: Thu, 15 Dec 2011 10:57:48 +1300
Subject: [PATCH] Support executing cleanup code when backtracking

Support executing cleanup code when backtracking
---
 src/gnu/prolog/vm/BacktrackInfoWithCleanup.java |   63 +++++++++++++++++++++++
 src/gnu/prolog/vm/Interpreter.java              |   12 ++++
 2 files changed, 75 insertions(+), 0 deletions(-)
 create mode 100644 src/gnu/prolog/vm/BacktrackInfoWithCleanup.java

diff --git a/src/gnu/prolog/vm/BacktrackInfoWithCleanup.java b/src/gnu/prolog/vm/BacktrackInfoWithCleanup.java
new file mode 100644
index 0000000..57e78b6
--- /dev/null
+++ b/src/gnu/prolog/vm/BacktrackInfoWithCleanup.java
@@ -0,0 +1,63 @@
+/* GNU Prolog for Java
+ * Copyright (C) 1997-1999  Constantine Plotnikov
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA  02111-1307, USA. The text of license can be also found
+ * at http://www.gnu.org/copyleft/lgpl.html
+ */
+package gnu.prolog.vm;
+
+import gnu.prolog.term.Term;
+
+/** back track information with cleanup information included */
+public class BacktrackInfoWithCleanup extends BacktrackInfo
+{
+	/**
+	 * a constructor
+	 * 
+	 * @param undoPosition
+	 *          address@hidden #undoPosition}
+	 * @param codePosition
+	 *          address@hidden #codePosition}
+	 * @param cleanup
+	 *          address@hidden #codePosition}
+	 * */
+        public BacktrackInfoWithCleanup(int undoPosition, int codePosition, Term cleanup)
+	{
+               super(undoPosition, codePosition);
+               this.cleanup = cleanup;
+	}
+
+        public BacktrackInfoWithCleanup(BacktrackInfo backtrackInfo, Term cleanup)
+	{
+               super(backtrackInfo.undoPosition, backtrackInfo.codePosition);
+               this.cleanup = cleanup;               
+	}
+
+	private Term cleanup;
+
+        public void cleanup(Interpreter interpreter)
+        {
+                 if (cleanup != null)
+                 {                        
+                 	try
+                 	{
+                           gnu.prolog.vm.interpreter.Predicate_call.staticExecute(interpreter, false, cleanup);
+                        }
+                        catch(PrologException e)
+                        {
+                        	/* Ignore exceptions and return status for cleanup */
+                        }
+                 }
+        }
+}
diff --git a/src/gnu/prolog/vm/Interpreter.java b/src/gnu/prolog/vm/Interpreter.java
index da1be1e..7d148d2 100644
--- a/src/gnu/prolog/vm/Interpreter.java
+++ b/src/gnu/prolog/vm/Interpreter.java
@@ -142,6 +142,10 @@ public final class Interpreter implements HasEnvironment
 	public BacktrackInfo popBacktrackInfo()
 	{
 		BacktrackInfo rc = backtrackInfoStack[--backtrackInfoAmount];
+                if (rc instanceof BacktrackInfoWithCleanup)
+                {
+                   ((BacktrackInfoWithCleanup)rc).cleanup(this);
+                }
 		backtrackInfoStack[backtrackInfoAmount] = null;
 		return rc;
 	}
@@ -159,6 +163,10 @@ public final class Interpreter implements HasEnvironment
 		}
 		for (int i = pos + 1; i < backtrackInfoAmount; i++)
 		{
+                	if (backtrackInfoStack[i] instanceof BacktrackInfoWithCleanup)
+			{
+                        	((BacktrackInfoWithCleanup)backtrackInfoStack[i]).cleanup(this);
+			}
 			backtrackInfoStack[i] = null;
 		}
 		backtrackInfoAmount = pos + 1;
@@ -606,6 +614,10 @@ public final class Interpreter implements HasEnvironment
 
 		for (int i = 0; i < backtrackInfoAmount; i++)
 		{
+			if (backtrackInfoStack[i] instanceof BacktrackInfoWithCleanup)
+                        {
+                               ((BacktrackInfoWithCleanup)backtrackInfoStack[i]).cleanup(this);
+                        }
 			backtrackInfoStack[i] = null;
 		}
 		backtrackInfoAmount = 0;
-- 
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