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diff --git a/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/prioritystack/PriorityStack.java b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/prioritystack/PriorityStack.java
new file mode 100644
index 000000000..d35362a3c
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+++ b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/prioritystack/PriorityStack.java
@@ -0,0 +1,201 @@
+/*******************************************************************************
+ * Copyright (c) 2007, 2010 Association for Decentralized Information Management
+ * in Industry THTH ry.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     VTT Technical Research Centre of Finland - initial API and implementation
+ *******************************************************************************/
+
+package org.simantics.utils.datastructures.prioritystack;
+
+import java.lang.reflect.Array;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.Map;
+
+import org.simantics.utils.strings.EString;
+import org.simantics.utils.threads.IThreadWorkQueue;
+import org.simantics.utils.threads.SyncListenerList;
+
+
+/**
+ * Implementation to IPriorityStack.
+ * 
+ * <p>
+ * Note!
+ * getAllItems() is optimized for result with the penalty of slower add/remove methods. 
+ *
+ * @author Toni Kalajainen
+ * @param <E>
+ */
+public class PriorityStack<E> implements IPriorityStack<E> {
+	
+	@SuppressWarnings({ "rawtypes" })
+    private SyncListenerList<IPriorityStackListener> listeners =
+		new SyncListenerList<IPriorityStackListener>(IPriorityStackListener.class);
+	
+	private LinkedList<E> list = 
+		new LinkedList<E>(); 
+	
+	private E[] snapshotArray;
+	
+	private Map<E, Integer> priorities = 
+		new HashMap<E, Integer>(); 
+	
+	final Class<E> clazz;
+	
+	public PriorityStack(Class<E> clazz) {
+		this.clazz = clazz;
+		snapshotArray = createArray(0);
+	}
+	
+	@Override
+	public void add(E interactor, int priority) {
+		abu:
+		synchronized(this) {
+			if (list.contains(interactor))
+				throw new IllegalArgumentException("InteractorStack already contains item "+interactor);
+		
+			priorities.put(interactor, priority);
+		
+			if (list.size()==0)
+			{
+				list.add(interactor);
+				snapshotArray = createSnapshot(list);
+				break abu;
+			}
+				
+			ListIterator<E> li = list.listIterator();
+			while (li.hasNext()) {
+				E i = li.next();
+				double w = priorities.get( i );
+				if (w > priority) {
+					li.previous();
+					li.add(interactor);
+					snapshotArray = createSnapshot(list);
+					break abu;
+				}
+			}
+			list.addLast(interactor);
+			snapshotArray = createSnapshot(list);
+		}
+		fireInteractorAdded(interactor);		
+	}
+	
+	@Override
+	public boolean remove(E interactor) {
+		synchronized(this) {
+			if (!priorities.containsKey(interactor)) 
+				return false;
+			priorities.remove(interactor);
+			list.remove(interactor);
+			snapshotArray = createSnapshot(list);
+		}
+		fireInteractorRemoved(interactor);
+		return true;
+	}	
+
+	@Override
+	public synchronized Integer getPriority(E interactor) {
+		return priorities.get(interactor);
+	}	
+
+	@SuppressWarnings({ "unchecked" })
+	private E[] createArray(int length)
+	{
+		return (E[]) Array.newInstance(clazz, length);
+	}
+
+	E[] createSnapshot(List<E> list) {
+		E[] result = createArray(list.size());
+		int index = 0;
+		for (E i : list)
+			result[index++] = i; 
+		return result;
+	}
+		
+	public synchronized int indexOf(E item)
+	{
+		for (int i=0; i<snapshotArray.length; i++)
+			if (snapshotArray[i]==item)
+				return i;
+		return -1;
+	}	
+	
+	@Override
+	public synchronized E[] toArray() {
+		return snapshotArray;
+	}
+
+	public synchronized <R extends E> R getSingleItem(Class<R> clazz)
+	{
+		R array[] = getItemsByClass(clazz);
+		if (array.length!=1)
+			throw new RuntimeException("one "+clazz.getName()+" expected in PriorityStack, got "+array.length);
+		return (R) array[0];
+	}
+	
+	@SuppressWarnings("unchecked")
+    @Override
+	public synchronized <R extends E> R[] getItemsByClass(Class<R> clazz)
+	{
+		List<E> result = new ArrayList<E>(list.size());
+		for (E i : list)
+			if (clazz.isAssignableFrom(i.getClass()))
+				result.add(i);
+		return (R[])result.toArray(createArray(result.size()));
+	}
+
+	private static Method itemAdded = SyncListenerList.getMethod(IPriorityStackListener.class, "itemAdded");
+	private void fireInteractorAdded(E interactor)
+	{
+		listeners.fireEventSync(itemAdded, this, interactor);
+	}
+	
+	private static Method itemRemoved = SyncListenerList.getMethod(IPriorityStackListener.class, "itemRemoved");
+	private void fireInteractorRemoved(E interactor)
+	{
+		listeners.fireEventSync(itemRemoved, this, interactor);
+	}
+
+	@Override
+	public synchronized void addStackListener(IPriorityStackListener<E> listener) {
+		listeners.add(listener);
+	}
+
+	@Override
+	public synchronized void removeStackListener(IPriorityStackListener<E> listener) {
+		listeners.remove(listener);
+	}
+
+	@Override
+	public synchronized boolean contains(E interactor) {
+		return list.contains(interactor);
+	}
+
+	@Override
+	public void addStackListener(IThreadWorkQueue thread,
+			IPriorityStackListener<E> listener) {
+		listeners.add(thread, listener);
+	}
+
+	@Override
+	public void removeStackListener(IThreadWorkQueue thread,
+			IPriorityStackListener<E> listener) {
+		listeners.remove(thread, listener);
+	}
+
+	@Override
+	public String toString() {
+	    return EString.implode(snapshotArray, "\n");
+	}
+
+}