--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hg4j/src/main/java/org/tmatesoft/hg/util/CancelSupport.java	Tue May 10 10:52:53 2011 +0200
@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2011 TMate Software Ltd
+ *  
+ * This program 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; version 2 of the License.
+ *
+ * This program 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.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.util;
+
+/**
+ * Mix-in for objects that support cancellation. 
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+public interface CancelSupport {
+
+	/**
+	 * This method is invoked to check if target had been brought to canceled state. Shall silently return if target is
+	 * in regular state.
+	 * @throws CancelledException when target internal state has been changed to canceled.
+	 */
+	void checkCancelled() throws CancelledException;
+
+
+	// Yeah, this factory class looks silly now, but perhaps in the future I'll need wrappers for other cancellation sources?
+	// just don't want to have general Utils class with methods like get() below
+	static class Factory {
+
+		/**
+		 * Obtain non-null cancel support object.
+		 * 
+		 * @param target any object (or <code>null</code>) that might have cancel support
+		 * @return target if it's capable checking cancellation status or no-op implementation that never cancels.
+				 */
+		public static CancelSupport get(Object target) {
+			if (target instanceof  CancelSupport) {
+				return (CancelSupport) target;
+			}
+			if (target instanceof Adaptable) {
+				CancelSupport cs = ((Adaptable) target).getAdapter(CancelSupport.class);
+				if (cs != null) {
+					return cs;
+				}
+			}
+			return new CancelSupport() {
+				public void checkCancelled() {
+				}
+			};
+		}
+	}
+}