Replaced the update lists with a priority queue implementation in LLClientView

Replaced the update lists with a priority queue implementation in LLClientView.
The priority queues are based on the MinHeap implementation also included in
this commit within the OpneSim.Framework namespace.  Initially setup to exactly
mimic the behavior beofre the change which was a first come first serve queue.

2 files changed, 554 insertions, 45 deletions

diff --git a/OpenSim/Framework/MinHeap.cs b/OpenSim/Framework/MinHeap.cs
new file mode 100755
index 0000000..ad39bbc
--- /dev/null
+++ b/OpenSim/Framework/MinHeap.cs
@@ -0,0 +1,375 @@
+using System;
+using System.Threading;
+using System.Collections;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+
+namespace OpenSim.Framework
+{
+    public interface IHandle { }
+
+    [Serializable, ComVisible(false)]
+    public class MinHeap<T> : ICollection<T>, ICollection
+    {
+        private class Handle : IHandle
+        {
+            internal int index = -1;
+            internal MinHeap<T> heap = null;
+
+            internal void Clear()
+            {
+                this.index = -1;
+                this.heap = null;
+            }
+        }
+
+        private struct HeapItem
+        {
+            internal T value;
+            internal Handle handle;
+
+            internal HeapItem(T value, Handle handle)
+            {
+                this.value = value;
+                this.handle = handle;
+            }
+
+            internal void Clear()
+            {
+                this.value = default(T);
+                if (this.handle != null)
+                {
+                    this.handle.Clear();
+                    this.handle = null;
+                }
+            }
+        }
+
+        public const int DEFAULT_CAPACITY = 4;
+
+        private HeapItem[] items;
+        private int size;
+        private object sync_root;
+        private int version;
+
+        private Comparison<T> comparison;
+
+        public MinHeap() : this(DEFAULT_CAPACITY, Comparer<T>.Default) { }
+        public MinHeap(int capacity) : this(capacity, Comparer<T>.Default) { }
+        public MinHeap(IComparer<T> comparer) : this(DEFAULT_CAPACITY, comparer) { }
+        public MinHeap(int capacity, IComparer<T> comparer) :
+            this(capacity, new Comparison<T>(comparer.Compare)) { }
+        public MinHeap(Comparison<T> comparison) : this(DEFAULT_CAPACITY, comparison) { }
+        public MinHeap(int capacity, Comparison<T> comparison)
+        {
+            this.items = new HeapItem[capacity];
+            this.comparison = comparison;
+            this.size = this.version = 0;
+        }
+
+        public int Count { get { return this.size; } }
+
+        public bool IsReadOnly { get { return false; } }
+
+        public bool IsSynchronized { get { return false; } }
+
+        public T this[IHandle key]
+        {
+            get
+            {
+                Handle handle = ValidateThisHandle(key);
+                return this.items[handle.index].value;
+            }
+
+            set
+            {
+                Handle handle = ValidateThisHandle(key);
+                this.items[handle.index].value = value;
+                if (!BubbleUp(handle.index))
+                    BubbleDown(handle.index);
+            }
+        }
+
+        public object SyncRoot
+        {
+            get
+            {
+                if (this.sync_root == null)
+                    Interlocked.CompareExchange<object>(ref this.sync_root, new object(), null);
+                return this.sync_root;
+            }
+        }
+
+        private Handle ValidateHandle(IHandle ihandle)
+        {
+            if (ihandle == null)
+                throw new ArgumentNullException("handle");
+            Handle handle = ihandle as Handle;
+            if (handle == null)
+                throw new InvalidOperationException("handle is not valid");
+            return handle;
+        }
+
+        private Handle ValidateThisHandle(IHandle ihandle)
+        {
+            Handle handle = ValidateHandle(ihandle);
+            if (!object.ReferenceEquals(handle.heap, this))
+                throw new InvalidOperationException("handle is not valid for this heap");
+            if (handle.index < 0)
+                throw new InvalidOperationException("handle is not associated to a value");
+            return handle;
+        }
+
+        private void Set(HeapItem item, int index)
+        {
+            this.items[index] = item;
+            if (item.handle != null)
+                item.handle.index = index;
+        }
+
+        private bool BubbleUp(int index)
+        {
+            HeapItem item = this.items[index];
+            int current, parent;
+
+            for (current = index, parent = (current - 1) / 2;
+                (current > 0) && (this.comparison(this.items[parent].value, item.value)) > 0;
+                current = parent, parent = (current - 1) / 2)
+            {
+                Set(this.items[parent], current);
+            }
+
+            if (current != index)
+            {
+                Set(item, current);
+                ++this.version;
+                return true;
+            }
+            return false;
+        }
+
+        private void BubbleDown(int index)
+        {
+            HeapItem item = this.items[index];
+            int current, child;
+
+            for (current = index, child = (2 * current) + 1;
+                current < this.size / 2;
+                current = child, child = (2 * current) + 1)
+            {
+                if ((child < this.size - 1) && this.comparison(this.items[child].value, this.items[child + 1].value) > 0)
+                    ++child;
+                if (this.comparison(this.items[child].value, item.value) >= 0)
+                    break;
+                Set(this.items[child], current);
+            }
+
+            if (current != index)
+            {
+                Set(item, current);
+                ++this.version;
+            }
+        }
+
+        public bool TryGetValue(IHandle key, out T value)
+        {
+            Handle handle = ValidateHandle(key);
+            if (handle.index > -1)
+            {
+                value = this.items[handle.index].value;
+                return true;
+            }
+            value = default(T);
+            return false;
+        }
+
+        public bool ContainsHandle(IHandle ihandle)
+        {
+            Handle handle = ValidateHandle(ihandle);
+            return object.ReferenceEquals(handle.heap, this) && handle.index > -1;
+        }
+
+        public void Add(T value, ref IHandle handle)
+        {
+            if (handle == null)
+                handle = new Handle();
+            Add(value, handle);
+        }
+
+        public void Add(T value, IHandle ihandle)
+        {
+            if (this.size == this.items.Length)
+            {
+                int capacity = (int)((this.items.Length * 200L) / 100L);
+                if (capacity < (this.items.Length + DEFAULT_CAPACITY))
+                    capacity = this.items.Length + DEFAULT_CAPACITY;
+                Array.Resize<HeapItem>(ref this.items, capacity);
+            }
+
+            Handle handle = null;
+            if (ihandle != null)
+            {
+                handle = ValidateHandle(ihandle);
+                handle.heap = this;
+            }
+
+            HeapItem item = new MinHeap<T>.HeapItem(value, handle);
+
+            Set(item, this.size);
+            BubbleUp(this.size++);
+        }
+
+        public void Add(T value)
+        {
+            Add(value, null);
+        }
+
+        public T Min()
+        {
+            if (this.size == 0)
+                throw new InvalidOperationException("Heap is empty");
+
+            return this.items[0].value;
+        }
+
+        public void Clear()
+        {
+            for (int index = 0; index < this.size; ++index)
+                this.items[index].Clear();
+            this.size = 0;
+            ++this.version;
+        }
+
+        public void TrimExcess()
+        {
+            int length = (int)(this.items.Length * 0.9);
+            if (this.size < length)
+                Array.Resize<HeapItem>(ref this.items, Math.Min(this.size, DEFAULT_CAPACITY));
+        }
+
+        private void RemoveAt(int index)
+        {
+            if (this.size == 0)
+                throw new InvalidOperationException("Heap is empty");
+            if (index >= this.size)
+                throw new ArgumentOutOfRangeException("index");
+
+            this.items[index].Clear();
+            if (--this.size > 0 && index != this.size)
+            {
+                Set(this.items[this.size], index);
+                if (!BubbleUp(index))
+                    BubbleDown(index);
+            }
+        }
+
+        public T RemoveMin()
+        {
+            if (this.size == 0)
+                throw new InvalidOperationException("Heap is empty");
+
+            HeapItem item = this.items[0];
+            RemoveAt(0);
+            return item.value;
+        }
+
+        public T Remove(IHandle ihandle)
+        {
+            Handle handle = ValidateThisHandle(ihandle);
+            HeapItem item = this.items[handle.index];
+            RemoveAt(handle.index);
+            return item.value;
+        }
+
+        private int GetIndex(T value)
+        {
+            EqualityComparer<T> comparer = EqualityComparer<T>.Default;
+            int index;
+
+            for (index = 0; index < this.size; ++index)
+            {
+                if (comparer.Equals(this.items[index].value, value))
+                    return index;
+            }
+            return -1;
+        }
+
+        public bool Contains(T value)
+        {
+            return GetIndex(value) != -1;
+        }
+
+        public bool Remove(T value)
+        {
+            int index = GetIndex(value);
+            if (index != -1)
+            {
+                RemoveAt(index);
+                return true;
+            }
+            return false;
+        }
+
+        public void CopyTo(T[] array, int index)
+        {
+            if (array == null)
+                throw new ArgumentNullException("array");
+            if (array.Rank != 1)
+                throw new ArgumentException("Multidimensional array not supported");
+            if (array.GetLowerBound(0) != 0)
+                throw new ArgumentException("Non-zero lower bound array not supported");
+
+            int length = array.Length;
+            if ((index < 0) || (index > length))
+                throw new ArgumentOutOfRangeException("index");
+            if ((length - index) < this.size)
+                throw new ArgumentException("Not enough space available in array starting at index");
+
+            for (int i = 0; i < this.size; ++i)
+                array[index + i] = this.items[i].value;
+        }
+
+        public void CopyTo(Array array, int index)
+        {
+            if (array == null)
+                throw new ArgumentNullException("array");
+            if (array.Rank != 1)
+                throw new ArgumentException("Multidimensional array not supported");
+            if (array.GetLowerBound(0) != 0)
+                throw new ArgumentException("Non-zero lower bound array not supported");
+
+            int length = array.Length;
+            if ((index < 0) || (index > length))
+                throw new ArgumentOutOfRangeException("index");
+            if ((length - index) < this.size)
+                throw new ArgumentException("Not enough space available in array starting at index");
+
+            try
+            {
+                for (int i = 0; i < this.size; ++i)
+                    array.SetValue(this.items[i].value, index + i);
+            }
+            catch (ArrayTypeMismatchException)
+            {
+                throw new ArgumentException("Invalid array type");
+            }
+        }
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            int version = this.version;
+
+            for (int index = 0; index < this.size; ++index)
+            {
+                if (version != this.version)
+                    throw new InvalidOperationException("Heap was modified while enumerating");
+                yield return this.items[index].value;
+            }
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+    }
+}
diff --git a/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs b/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
index 82a2cdd..93fdeef 100644
--- a/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
+++ b/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
@@ -321,11 +321,14 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         private int m_cachedTextureSerial;
         private Timer m_avatarTerseUpdateTimer;
-        private List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock> m_avatarTerseUpdates = new List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
+        private PriorityQueue<double, ImprovedTerseObjectUpdatePacket.ObjectDataBlock> m_avatarTerseUpdates_ =
+            new PriorityQueue<double, ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
         private Timer m_primTerseUpdateTimer;
-        private List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock> m_primTerseUpdates = new List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
+        private PriorityQueue<double, ImprovedTerseObjectUpdatePacket.ObjectDataBlock> m_primTerseUpdates_ =
+            new PriorityQueue<double, ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
         private Timer m_primFullUpdateTimer;
-        private List<ObjectUpdatePacket.ObjectDataBlock> m_primFullUpdates = new List<ObjectUpdatePacket.ObjectDataBlock>();
+        private PriorityQueue<double, ObjectUpdatePacket.ObjectDataBlock> m_primFullUpdates_ =
+            new PriorityQueue<double, ObjectUpdatePacket.ObjectDataBlock>();
         private int m_moneyBalance;
         private int m_animationSequenceNumber = 1;
         private bool m_SendLogoutPacketWhenClosing = true;
@@ -3435,16 +3438,16 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             ImprovedTerseObjectUpdatePacket.ObjectDataBlock terseBlock =
                 CreateAvatarImprovedBlock(localID, position, velocity,rotation);
                 
-            lock (m_avatarTerseUpdates)
+            lock (m_avatarTerseUpdates_.SyncRoot)
             {
-                m_avatarTerseUpdates.Add(terseBlock);
+                m_avatarTerseUpdates_.Enqueue(DateTime.Now.ToOADate(), terseBlock, localID);
 
                 // If packet is full or own movement packet, send it.
-                if (m_avatarTerseUpdates.Count >= m_avatarTerseUpdatesPerPacket)
+                if (m_avatarTerseUpdates_.Count >= m_avatarTerseUpdatesPerPacket)
                 {
                     ProcessAvatarTerseUpdates(this, null);
                 }
-                else if (m_avatarTerseUpdates.Count == 1)
+                else if (m_avatarTerseUpdates_.Count == 1)
                 {
                     lock (m_avatarTerseUpdateTimer)
                         m_avatarTerseUpdateTimer.Start();
@@ -3454,7 +3457,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         private void ProcessAvatarTerseUpdates(object sender, ElapsedEventArgs e)
         {
-            lock (m_avatarTerseUpdates)
+            lock (m_avatarTerseUpdates_.SyncRoot)
             {
                 ImprovedTerseObjectUpdatePacket terse = (ImprovedTerseObjectUpdatePacket)PacketPool.Instance.GetPacket(PacketType.ImprovedTerseObjectUpdate);
 
@@ -3465,8 +3468,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                         (ushort)(Scene.TimeDilation * ushort.MaxValue);
 
                 int max = m_avatarTerseUpdatesPerPacket;
-                if (max > m_avatarTerseUpdates.Count)
-                    max = m_avatarTerseUpdates.Count;
+                if (max > m_avatarTerseUpdates_.Count)
+                    max = m_avatarTerseUpdates_.Count;
 
                 int count = 0;
                 int size = 0;
@@ -3474,30 +3477,30 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 byte[] zerobuffer = new byte[1024];
                 byte[] blockbuffer = new byte[1024];
 
+                Queue<ImprovedTerseObjectUpdatePacket.ObjectDataBlock> updates = new Queue<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
+
                 for (count = 0 ; count < max ; count++)
                 {
                     int length = 0;
-                    m_avatarTerseUpdates[count].ToBytes(blockbuffer, ref length);
+                    m_avatarTerseUpdates_.Peek().ToBytes(blockbuffer, ref length);
                     length = Helpers.ZeroEncode(blockbuffer, length, zerobuffer);
                     if (size + length > Packet.MTU)
                         break;
                     size += length;
+                    updates.Enqueue(m_avatarTerseUpdates_.Dequeue());
                 }
 
                 terse.ObjectData = new ImprovedTerseObjectUpdatePacket.ObjectDataBlock[count];
 
                 for (int i = 0 ; i < count ; i++)
-                {
-                    terse.ObjectData[i] = m_avatarTerseUpdates[0];
-                    m_avatarTerseUpdates.RemoveAt(0);
-                }
+                    terse.ObjectData[i] = updates.Dequeue();
 
                 terse.Header.Reliable = false;
                 terse.Header.Zerocoded = true;
                 // FIXME: Move this to ThrottleOutPacketType.State when the real prioritization code is committed
                 OutPacket(terse, ThrottleOutPacketType.Task);
 
-                if (m_avatarTerseUpdates.Count == 0)
+                if (m_avatarTerseUpdates_.Count == 0)
                 {
                     lock (m_avatarTerseUpdateTimer)
                         m_avatarTerseUpdateTimer.Stop();
@@ -3660,14 +3663,14 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 objectData.TextureAnim = textureanim;
             }
 
-            lock (m_primFullUpdates)
+            lock (m_primFullUpdates_.SyncRoot)
             {
-                if (m_primFullUpdates.Count == 0)
+                if (m_primFullUpdates_.Count == 0)
                     m_primFullUpdateTimer.Start();
 
-                m_primFullUpdates.Add(objectData);
+                m_primFullUpdates_.Enqueue(DateTime.Now.ToOADate(), objectData, localID);
 
-                if (m_primFullUpdates.Count >= m_primFullUpdatesPerPacket)
+                if (m_primFullUpdates_.Count >= m_primFullUpdatesPerPacket)
                     ProcessPrimFullUpdates(this, null);
             }
         }
@@ -3690,9 +3693,9 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         void ProcessPrimFullUpdates(object sender, ElapsedEventArgs e)
         {
-            lock (m_primFullUpdates)
+            lock (m_primFullUpdates_.SyncRoot)
             {
-                if (m_primFullUpdates.Count == 0 && m_primFullUpdateTimer.Enabled)
+                if (m_primFullUpdates_.Count == 0 && m_primFullUpdateTimer.Enabled)
                 {
                     lock (m_primFullUpdateTimer)
                         m_primFullUpdateTimer.Stop();
@@ -3709,7 +3712,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 outPacket.RegionData.TimeDilation =
                         (ushort)(Scene.TimeDilation * ushort.MaxValue);
 
-                int max = m_primFullUpdates.Count;
+                int max = m_primFullUpdates_.Count;
                 if (max > m_primFullUpdatesPerPacket)
                     max = m_primFullUpdatesPerPacket;
 
@@ -3719,29 +3722,29 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 byte[] zerobuffer = new byte[1024];
                 byte[] blockbuffer = new byte[1024];
 
+                Queue<ObjectUpdatePacket.ObjectDataBlock> updates = new Queue<ObjectUpdatePacket.ObjectDataBlock>();
+
                 for (count = 0 ; count < max ; count++)
                 {
                     int length = 0;
-                    m_primFullUpdates[count].ToBytes(blockbuffer, ref length);
+                    m_primFullUpdates_.Peek().ToBytes(blockbuffer, ref length);
                     length = Helpers.ZeroEncode(blockbuffer, length, zerobuffer);
                     if (size + length > Packet.MTU)
                         break;
                     size += length;
+                    updates.Enqueue(m_primFullUpdates_.Dequeue());
                 }
 
                 outPacket.ObjectData =
                         new ObjectUpdatePacket.ObjectDataBlock[count];
 
                 for (int index = 0 ; index < count ; index++)
-                {
-                    outPacket.ObjectData[index] = m_primFullUpdates[0];
-                    m_primFullUpdates.RemoveAt(0);
-                }
+                    outPacket.ObjectData[index] = updates.Dequeue();
 
                 outPacket.Header.Zerocoded = true;
                 OutPacket(outPacket, ThrottleOutPacketType.State);
 
-                if (m_primFullUpdates.Count == 0 && m_primFullUpdateTimer.Enabled)
+                if (m_primFullUpdates_.Count == 0 && m_primFullUpdateTimer.Enabled)
                     lock (m_primFullUpdateTimer)
                         m_primFullUpdateTimer.Stop();
             }
@@ -3763,23 +3766,23 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     CreatePrimImprovedBlock(localID, position, rotation,
                     velocity, rotationalvelocity, state);
 
-            lock (m_primTerseUpdates)
+            lock (m_primTerseUpdates_.SyncRoot)
             {
-                if (m_primTerseUpdates.Count == 0)
+                if (m_primTerseUpdates_.Count == 0)
                     m_primTerseUpdateTimer.Start();
 
-                m_primTerseUpdates.Add(objectData);
+                m_primTerseUpdates_.Enqueue(DateTime.Now.ToOADate(), objectData, localID);
 
-                if (m_primTerseUpdates.Count >= m_primTerseUpdatesPerPacket)
+                if (m_primTerseUpdates_.Count >= m_primTerseUpdatesPerPacket)
                     ProcessPrimTerseUpdates(this, null);
             }
         }
 
         void ProcessPrimTerseUpdates(object sender, ElapsedEventArgs e)
         {
-            lock (m_primTerseUpdates)
+            lock (m_primTerseUpdates_.SyncRoot)
             {
-                if (m_primTerseUpdates.Count == 0)
+                if (m_primTerseUpdates_.Count == 0)
                 {
                     lock (m_primTerseUpdateTimer)
                         m_primTerseUpdateTimer.Stop();
@@ -3797,7 +3800,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 outPacket.RegionData.TimeDilation =
                         (ushort)(Scene.TimeDilation * ushort.MaxValue);
 
-                int max = m_primTerseUpdates.Count;
+                int max = m_primTerseUpdates_.Count;
                 if (max > m_primTerseUpdatesPerPacket)
                     max = m_primTerseUpdatesPerPacket;
 
@@ -3807,14 +3810,17 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 byte[] zerobuffer = new byte[1024];
                 byte[] blockbuffer = new byte[1024];
 
+                Queue<ImprovedTerseObjectUpdatePacket.ObjectDataBlock> updates = new Queue<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>();
+
                 for (count = 0 ; count < max ; count++)
                 {
                     int length = 0;
-                    m_primTerseUpdates[count].ToBytes(blockbuffer, ref length);
+                    m_primTerseUpdates_.Peek().ToBytes(blockbuffer, ref length);
                     length = Helpers.ZeroEncode(blockbuffer, length, zerobuffer);
                     if (size + length > Packet.MTU)
                         break;
                     size += length;
+                    updates.Enqueue(m_primTerseUpdates_.Dequeue());
                 }
 
                 outPacket.ObjectData =
@@ -3822,16 +3828,13 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                         ObjectDataBlock[count];
 
                 for (int index = 0 ; index < count ; index++)
-                {
-                    outPacket.ObjectData[index] = m_primTerseUpdates[0];
-                    m_primTerseUpdates.RemoveAt(0);
-                }
+                    outPacket.ObjectData[index] = updates.Dequeue();
 
                 outPacket.Header.Reliable = false;
                 outPacket.Header.Zerocoded = true;
                 OutPacket(outPacket, ThrottleOutPacketType.State);
 
-                if (m_primTerseUpdates.Count == 0)
+                if (m_primTerseUpdates_.Count == 0)
                     lock (m_primTerseUpdateTimer)
                         m_primTerseUpdateTimer.Stop();
             }
@@ -3839,15 +3842,15 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         public void FlushPrimUpdates()
         {
-            while (m_primFullUpdates.Count > 0)
+            while (m_primFullUpdates_.Count > 0)
             {
                 ProcessPrimFullUpdates(this, null);
             }
-            while (m_primTerseUpdates.Count > 0)
+            while (m_primTerseUpdates_.Count > 0)
             {
                 ProcessPrimTerseUpdates(this, null);
             }
-            while (m_avatarTerseUpdates.Count > 0)
+            while (m_avatarTerseUpdates_.Count > 0)
             {
                 ProcessAvatarTerseUpdates(this, null);
             }
@@ -10578,5 +10581,136 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             pack.TextureData.TextureID = textureID;
             OutPacket(pack, ThrottleOutPacketType.Task);
         }
+
+        #region PriorityQueue
+        private class PriorityQueue<TPriority, TValue>
+        {
+            private MinHeap<MinHeapItem>[] heaps = new MinHeap<MinHeapItem>[1];
+            private Dictionary<uint, LookupItem> lookup_table = new Dictionary<uint, LookupItem>();
+            private Comparison<TPriority> comparison;
+            private object sync_root = new object();
+
+            internal PriorityQueue() :
+                this(MinHeap<MinHeapItem>.DEFAULT_CAPACITY, Comparer<TPriority>.Default) { }
+            internal PriorityQueue(int capacity) :
+                this(capacity, Comparer<TPriority>.Default) { }
+            internal PriorityQueue(IComparer<TPriority> comparer) :
+                this(new Comparison<TPriority>(comparer.Compare)) { }
+            internal PriorityQueue(Comparison<TPriority> comparison) :
+                this(MinHeap<MinHeapItem>.DEFAULT_CAPACITY, comparison) { }
+            internal PriorityQueue(int capacity, IComparer<TPriority> comparer) :
+                this(capacity, new Comparison<TPriority>(comparer.Compare)) { }
+            internal PriorityQueue(int capacity, Comparison<TPriority> comparison)
+            {
+                for (int i = 0; i < heaps.Length; ++i)
+                    heaps[i] = new MinHeap<MinHeapItem>(capacity);
+                this.comparison = comparison;
+            }
+
+            internal object SyncRoot { get { return this.sync_root; } }
+            internal int Count
+            {
+                get
+                {
+                    int count = 0;
+                    for (int i = 0; i < heaps.Length; ++i)
+                        count = heaps[i].Count;
+                    return count;
+                }
+            }
+
+            internal bool Enqueue(TPriority priority, TValue value, uint local_id)
+            {
+                LookupItem item;
+
+                if (lookup_table.TryGetValue(local_id, out item))
+                {
+                    item.Heap[item.Handle] = new MinHeapItem(priority, value, local_id, this.comparison);
+                    return false;
+                }
+                else
+                {
+                    item.Heap = heaps[0];
+                    item.Heap.Add(new MinHeapItem(priority, value, local_id, this.comparison), ref item.Handle);
+                    lookup_table.Add(local_id, item);
+                    return true;
+                }
+            }
+
+            internal TValue Peek()
+            {
+                for (int i = 0; i < heaps.Length; ++i)
+                    if (heaps[i].Count > 0)
+                        return heaps[i].Min().Value;
+                throw new InvalidOperationException(string.Format("The {0} is empty", this.GetType().ToString()));
+            }
+
+            internal TValue Dequeue()
+            {
+                for (int i = 0; i < heaps.Length; ++i)
+                {
+                    if (heaps[i].Count > 0)
+                    {
+                        MinHeapItem item = heaps[i].RemoveMin();
+                        lookup_table.Remove(item.LocalID);
+                        return item.Value;
+                    }
+                }
+                throw new InvalidOperationException(string.Format("The {0} is empty", this.GetType().ToString()));
+            }
+
+            #region MinHeapItem
+            private struct MinHeapItem : IComparable<MinHeapItem>
+            {
+                private TPriority priority;
+                private TValue value;
+                private uint local_id;
+                private Comparison<TPriority> comparison;
+
+                internal MinHeapItem(TPriority priority, TValue value, uint local_id) :
+                    this(priority, value, local_id, Comparer<TPriority>.Default) { }
+                internal MinHeapItem(TPriority priority, TValue value, uint local_id, IComparer<TPriority> comparer) :
+                    this(priority, value, local_id, new Comparison<TPriority>(comparer.Compare)) { }
+                internal MinHeapItem(TPriority priority, TValue value, uint local_id, Comparison<TPriority> comparison)
+                {
+                    this.priority = priority;
+                    this.value = value;
+                    this.local_id = local_id;
+                    this.comparison = comparison;
+                }
+
+                internal TPriority Priority { get { return this.priority; } }
+                internal TValue Value { get { return this.value; } }
+                internal uint LocalID { get { return this.local_id; } }
+
+                public override string ToString()
+                {
+                    StringBuilder sb = new StringBuilder();
+                    sb.Append("[");
+                    if (this.priority != null)
+                        sb.Append(this.priority.ToString());
+                    sb.Append(",");
+                    if (this.value != null)
+                        sb.Append(this.value.ToString());
+                    sb.Append("]");
+                    return sb.ToString();
+                }
+
+                public int CompareTo(MinHeapItem other)
+                {
+                    return this.comparison(this.priority, other.priority);
+                }
+            }
+            #endregion
+
+            #region LookupItem
+            private struct LookupItem {
+                internal MinHeap<MinHeapItem> Heap;
+                internal IHandle Handle;
+            }
+            #endregion
+        }
+        #endregion
+
     }
 }