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diff --git a/OpenSim/Framework/MapAndArray.cs b/OpenSim/Framework/MapAndArray.cs
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+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSimulator Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+using System;
+using System.Collections.Generic;
+
+namespace OpenSim.Framework
+{
+    /// <summary>
+    /// Stores two synchronized collections: a mutable dictionary and an
+    /// immutable array. Slower inserts/removes than a normal dictionary,
+    /// but provides safe iteration while maintaining fast hash lookups
+    /// </summary>
+    /// <typeparam name="TKey">Key type to use for hash lookups</typeparam>
+    /// <typeparam name="TValue">Value type to store</typeparam>
+    public sealed class MapAndArray<TKey, TValue>
+    {
+        private Dictionary<TKey, TValue> m_dict;
+        private TValue[] m_array;
+        private object m_syncRoot = new object();
+
+        /// <summary>Number of values currently stored in the collection</summary>
+        public int Count { get { return m_array.Length; } }
+        /// <summary>NOTE: This collection is thread safe. You do not need to 
+        /// acquire a lock to add, remove, or enumerate entries. This 
+        /// synchronization object should only be locked for larger 
+        /// transactions</summary>
+        public object SyncRoot { get { return m_syncRoot; } }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        public MapAndArray()
+        {
+            m_dict = new Dictionary<TKey, TValue>();
+            m_array = new TValue[0];
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="capacity">Initial capacity of the dictionary</param>
+        public MapAndArray(int capacity)
+        {
+            m_dict = new Dictionary<TKey, TValue>(capacity);
+            m_array = new TValue[0];
+        }
+
+        /// <summary>
+        /// Adds a key/value pair to the collection, or updates an existing key
+        /// with a new value
+        /// </summary>
+        /// <param name="key">Key to add or update</param>
+        /// <param name="value">Value to add</param>
+        /// <returns>True if a new key was added, false if an existing key was
+        /// updated</returns>
+        public bool AddOrReplace(TKey key, TValue value)
+        {
+            lock (m_syncRoot)
+            {
+                bool containedKey = m_dict.ContainsKey(key);
+
+                m_dict[key] = value;
+                CreateArray();
+
+                return !containedKey;
+            }
+        }
+
+        /// <summary>
+        /// Adds a key/value pair to the collection. This will throw an 
+        /// exception if the key is already present in the collection
+        /// </summary>
+        /// <param name="key">Key to add or update</param>
+        /// <param name="value">Value to add</param>
+        /// <returns>Index of the inserted item</returns>
+        public int Add(TKey key, TValue value)
+        {
+            lock (m_syncRoot)
+            {
+                m_dict.Add(key, value);
+                CreateArray();
+                return m_array.Length;
+            }
+        }
+
+        /// <summary>
+        /// Removes a key/value pair from the collection
+        /// </summary>
+        /// <param name="key">Key to remove</param>
+        /// <returns>True if the key was found and removed, otherwise false</returns>
+        public bool Remove(TKey key)
+        {
+            lock (m_syncRoot)
+            {
+                bool removed = m_dict.Remove(key);
+                CreateArray();
+
+                return removed;
+            }
+        }
+
+        /// <summary>
+        /// Determines whether the collections contains a specified key
+        /// </summary>
+        /// <param name="key">Key to search for</param>
+        /// <returns>True if the key was found, otherwise false</returns>
+        public bool ContainsKey(TKey key)
+        {
+            return m_dict.ContainsKey(key);
+        }
+
+        /// <summary>
+        /// Gets the value associated with the specified key
+        /// </summary>
+        /// <param name="key">Key of the value to get</param>
+        /// <param name="value">Will contain the value associated with the
+        /// given key if the key is found. If the key is not found it will
+        /// contain the default value for the type of the value parameter</param>
+        /// <returns>True if the key was found and a value was retrieved,
+        /// otherwise false</returns>
+        public bool TryGetValue(TKey key, out TValue value)
+        {
+            lock (m_syncRoot)
+                return m_dict.TryGetValue(key, out value);
+        }
+
+        /// <summary>
+        /// Clears all key/value pairs from the collection
+        /// </summary>
+        public void Clear()
+        {
+            lock (m_syncRoot)
+            {
+                m_dict = new Dictionary<TKey, TValue>();
+                m_array = new TValue[0];
+            }
+        }
+
+        /// <summary>
+        /// Gets a reference to the immutable array of values stored in this
+        /// collection. This array is thread safe for iteration
+        /// </summary>
+        /// <returns>A thread safe reference ton an array of all of the stored 
+        /// values</returns>
+        public TValue[] GetArray()
+        {
+            return m_array;
+        }
+
+        private void CreateArray()
+        {
+            // Rebuild the array from the dictionary. This method must be 
+            // called from inside a lock
+            TValue[] array = new TValue[m_dict.Count];
+            int i = 0;
+
+            foreach (TValue value in m_dict.Values)
+                array[i++] = value;
+
+            m_array = array;
+        }
+    }
+}