Merge pull request #2603 from MediaBrowser/dev

Dev

6 files changed, 797 insertions, 9 deletions

diff --git a/MediaBrowser.Providers/Manager/GenericPriorityQueue.cs b/MediaBrowser.Providers/Manager/GenericPriorityQueue.cs
new file mode 100644
index 000000000..18998fd59
--- /dev/null
+++ b/MediaBrowser.Providers/Manager/GenericPriorityQueue.cs
@@ -0,0 +1,426 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Priority_Queue
+{
+    /// <summary>
+    /// Credit: https://github.com/BlueRaja/High-Speed-Priority-Queue-for-C-Sharp
+    /// A copy of StablePriorityQueue which also has generic priority-type
+    /// </summary>
+    /// <typeparam name="TItem">The values in the queue.  Must extend the GenericPriorityQueue class</typeparam>
+    /// <typeparam name="TPriority">The priority-type.  Must extend IComparable&lt;TPriority&gt;</typeparam>
+    public sealed class GenericPriorityQueue<TItem, TPriority> : IFixedSizePriorityQueue<TItem, TPriority>
+        where TItem : GenericPriorityQueueNode<TPriority>
+        where TPriority : IComparable<TPriority>
+    {
+        private int _numNodes;
+        private TItem[] _nodes;
+        private long _numNodesEverEnqueued;
+
+        /// <summary>
+        /// Instantiate a new Priority Queue
+        /// </summary>
+        /// <param name="maxNodes">The max nodes ever allowed to be enqueued (going over this will cause undefined behavior)</param>
+        public GenericPriorityQueue(int maxNodes)
+        {
+#if DEBUG
+            if (maxNodes <= 0)
+            {
+                throw new InvalidOperationException("New queue size cannot be smaller than 1");
+            }
+#endif
+
+            _numNodes = 0;
+            _nodes = new TItem[maxNodes + 1];
+            _numNodesEverEnqueued = 0;
+        }
+
+        /// <summary>
+        /// Returns the number of nodes in the queue.
+        /// O(1)
+        /// </summary>
+        public int Count
+        {
+            get
+            {
+                return _numNodes;
+            }
+        }
+
+        /// <summary>
+        /// Returns the maximum number of items that can be enqueued at once in this queue.  Once you hit this number (ie. once Count == MaxSize),
+        /// attempting to enqueue another item will cause undefined behavior.  O(1)
+        /// </summary>
+        public int MaxSize
+        {
+            get
+            {
+                return _nodes.Length - 1;
+            }
+        }
+
+        /// <summary>
+        /// Removes every node from the queue.
+        /// O(n) (So, don't do this often!)
+        /// </summary>
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        public void Clear()
+        {
+            Array.Clear(_nodes, 1, _numNodes);
+            _numNodes = 0;
+        }
+
+        /// <summary>
+        /// Returns (in O(1)!) whether the given node is in the queue.  O(1)
+        /// </summary>
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        public bool Contains(TItem node)
+        {
+#if DEBUG
+            if (node == null)
+            {
+                throw new ArgumentNullException("node");
+            }
+            if (node.QueueIndex < 0 || node.QueueIndex >= _nodes.Length)
+            {
+                throw new InvalidOperationException("node.QueueIndex has been corrupted. Did you change it manually? Or add this node to another queue?");
+            }
+#endif
+
+            return (_nodes[node.QueueIndex] == node);
+        }
+
+        /// <summary>
+        /// Enqueue a node to the priority queue.  Lower values are placed in front. Ties are broken by first-in-first-out.
+        /// If the queue is full, the result is undefined.
+        /// If the node is already enqueued, the result is undefined.
+        /// O(log n)
+        /// </summary>
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        public void Enqueue(TItem node, TPriority priority)
+        {
+#if DEBUG
+            if (node == null)
+            {
+                throw new ArgumentNullException("node");
+            }
+            if (_numNodes >= _nodes.Length - 1)
+            {
+                throw new InvalidOperationException("Queue is full - node cannot be added: " + node);
+            }
+            if (Contains(node))
+            {
+                throw new InvalidOperationException("Node is already enqueued: " + node);
+            }
+#endif
+
+            node.Priority = priority;
+            _numNodes++;
+            _nodes[_numNodes] = node;
+            node.QueueIndex = _numNodes;
+            node.InsertionIndex = _numNodesEverEnqueued++;
+            CascadeUp(_nodes[_numNodes]);
+        }
+
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        private void Swap(TItem node1, TItem node2)
+        {
+            //Swap the nodes
+            _nodes[node1.QueueIndex] = node2;
+            _nodes[node2.QueueIndex] = node1;
+
+            //Swap their indicies
+            int temp = node1.QueueIndex;
+            node1.QueueIndex = node2.QueueIndex;
+            node2.QueueIndex = temp;
+        }
+
+        //Performance appears to be slightly better when this is NOT inlined o_O
+        private void CascadeUp(TItem node)
+        {
+            //aka Heapify-up
+            int parent = node.QueueIndex / 2;
+            while (parent >= 1)
+            {
+                TItem parentNode = _nodes[parent];
+                if (HasHigherPriority(parentNode, node))
+                    break;
+
+                //Node has lower priority value, so move it up the heap
+                Swap(node, parentNode); //For some reason, this is faster with Swap() rather than (less..?) individual operations, like in CascadeDown()
+
+                parent = node.QueueIndex / 2;
+            }
+        }
+
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        private void CascadeDown(TItem node)
+        {
+            //aka Heapify-down
+            TItem newParent;
+            int finalQueueIndex = node.QueueIndex;
+            while (true)
+            {
+                newParent = node;
+                int childLeftIndex = 2 * finalQueueIndex;
+
+                //Check if the left-child is higher-priority than the current node
+                if (childLeftIndex > _numNodes)
+                {
+                    //This could be placed outside the loop, but then we'd have to check newParent != node twice
+                    node.QueueIndex = finalQueueIndex;
+                    _nodes[finalQueueIndex] = node;
+                    break;
+                }
+
+                TItem childLeft = _nodes[childLeftIndex];
+                if (HasHigherPriority(childLeft, newParent))
+                {
+                    newParent = childLeft;
+                }
+
+                //Check if the right-child is higher-priority than either the current node or the left child
+                int childRightIndex = childLeftIndex + 1;
+                if (childRightIndex <= _numNodes)
+                {
+                    TItem childRight = _nodes[childRightIndex];
+                    if (HasHigherPriority(childRight, newParent))
+                    {
+                        newParent = childRight;
+                    }
+                }
+
+                //If either of the children has higher (smaller) priority, swap and continue cascading
+                if (newParent != node)
+                {
+                    //Move new parent to its new index.  node will be moved once, at the end
+                    //Doing it this way is one less assignment operation than calling Swap()
+                    _nodes[finalQueueIndex] = newParent;
+
+                    int temp = newParent.QueueIndex;
+                    newParent.QueueIndex = finalQueueIndex;
+                    finalQueueIndex = temp;
+                }
+                else
+                {
+                    //See note above
+                    node.QueueIndex = finalQueueIndex;
+                    _nodes[finalQueueIndex] = node;
+                    break;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Returns true if 'higher' has higher priority than 'lower', false otherwise.
+        /// Note that calling HasHigherPriority(node, node) (ie. both arguments the same node) will return false
+        /// </summary>
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        private bool HasHigherPriority(TItem higher, TItem lower)
+        {
+            var cmp = higher.Priority.CompareTo(lower.Priority);
+            return (cmp < 0 || (cmp == 0 && higher.InsertionIndex < lower.InsertionIndex));
+        }
+
+        /// <summary>
+        /// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
+        /// If queue is empty, result is undefined
+        /// O(log n)
+        /// </summary>
+        public TItem Dequeue()
+        {
+#if DEBUG
+            if (_numNodes <= 0)
+            {
+                throw new InvalidOperationException("Cannot call Dequeue() on an empty queue");
+            }
+
+            if (!IsValidQueue())
+            {
+                throw new InvalidOperationException("Queue has been corrupted (Did you update a node priority manually instead of calling UpdatePriority()?" +
+                                                    "Or add the same node to two different queues?)");
+            }
+#endif
+
+            TItem returnMe = _nodes[1];
+            Remove(returnMe);
+            return returnMe;
+        }
+
+        /// <summary>
+        /// Resize the queue so it can accept more nodes.  All currently enqueued nodes are remain.
+        /// Attempting to decrease the queue size to a size too small to hold the existing nodes results in undefined behavior
+        /// O(n)
+        /// </summary>
+        public void Resize(int maxNodes)
+        {
+#if DEBUG
+            if (maxNodes <= 0)
+            {
+                throw new InvalidOperationException("Queue size cannot be smaller than 1");
+            }
+
+            if (maxNodes < _numNodes)
+            {
+                throw new InvalidOperationException("Called Resize(" + maxNodes + "), but current queue contains " + _numNodes + " nodes");
+            }
+#endif
+
+            TItem[] newArray = new TItem[maxNodes + 1];
+            int highestIndexToCopy = Math.Min(maxNodes, _numNodes);
+            for (int i = 1; i <= highestIndexToCopy; i++)
+            {
+                newArray[i] = _nodes[i];
+            }
+            _nodes = newArray;
+        }
+
+        /// <summary>
+        /// Returns the head of the queue, without removing it (use Dequeue() for that).
+        /// If the queue is empty, behavior is undefined.
+        /// O(1)
+        /// </summary>
+        public TItem First
+        {
+            get
+            {
+#if DEBUG
+                if (_numNodes <= 0)
+                {
+                    throw new InvalidOperationException("Cannot call .First on an empty queue");
+                }
+#endif
+
+                return _nodes[1];
+            }
+        }
+
+        /// <summary>
+        /// This method must be called on a node every time its priority changes while it is in the queue.  
+        /// <b>Forgetting to call this method will result in a corrupted queue!</b>
+        /// Calling this method on a node not in the queue results in undefined behavior
+        /// O(log n)
+        /// </summary>
+#if NET_VERSION_4_5
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        public void UpdatePriority(TItem node, TPriority priority)
+        {
+#if DEBUG
+            if (node == null)
+            {
+                throw new ArgumentNullException("node");
+            }
+            if (!Contains(node))
+            {
+                throw new InvalidOperationException("Cannot call UpdatePriority() on a node which is not enqueued: " + node);
+            }
+#endif
+
+            node.Priority = priority;
+            OnNodeUpdated(node);
+        }
+
+        private void OnNodeUpdated(TItem node)
+        {
+            //Bubble the updated node up or down as appropriate
+            int parentIndex = node.QueueIndex / 2;
+            TItem parentNode = _nodes[parentIndex];
+
+            if (parentIndex > 0 && HasHigherPriority(node, parentNode))
+            {
+                CascadeUp(node);
+            }
+            else
+            {
+                //Note that CascadeDown will be called if parentNode == node (that is, node is the root)
+                CascadeDown(node);
+            }
+        }
+
+        /// <summary>
+        /// Removes a node from the queue.  The node does not need to be the head of the queue.  
+        /// If the node is not in the queue, the result is undefined.  If unsure, check Contains() first
+        /// O(log n)
+        /// </summary>
+        public void Remove(TItem node)
+        {
+#if DEBUG
+            if (node == null)
+            {
+                throw new ArgumentNullException("node");
+            }
+            if (!Contains(node))
+            {
+                throw new InvalidOperationException("Cannot call Remove() on a node which is not enqueued: " + node);
+            }
+#endif
+
+            //If the node is already the last node, we can remove it immediately
+            if (node.QueueIndex == _numNodes)
+            {
+                _nodes[_numNodes] = null;
+                _numNodes--;
+                return;
+            }
+
+            //Swap the node with the last node
+            TItem formerLastNode = _nodes[_numNodes];
+            Swap(node, formerLastNode);
+            _nodes[_numNodes] = null;
+            _numNodes--;
+
+            //Now bubble formerLastNode (which is no longer the last node) up or down as appropriate
+            OnNodeUpdated(formerLastNode);
+        }
+
+        public IEnumerator<TItem> GetEnumerator()
+        {
+            for (int i = 1; i <= _numNodes; i++)
+                yield return _nodes[i];
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        /// <summary>
+        /// <b>Should not be called in production code.</b>
+        /// Checks to make sure the queue is still in a valid state.  Used for testing/debugging the queue.
+        /// </summary>
+        public bool IsValidQueue()
+        {
+            for (int i = 1; i < _nodes.Length; i++)
+            {
+                if (_nodes[i] != null)
+                {
+                    int childLeftIndex = 2 * i;
+                    if (childLeftIndex < _nodes.Length && _nodes[childLeftIndex] != null && HasHigherPriority(_nodes[childLeftIndex], _nodes[i]))
+                        return false;
+
+                    int childRightIndex = childLeftIndex + 1;
+                    if (childRightIndex < _nodes.Length && _nodes[childRightIndex] != null && HasHigherPriority(_nodes[childRightIndex], _nodes[i]))
+                        return false;
+                }
+            }
+            return true;
+        }
+    }
+}
diff --git a/MediaBrowser.Providers/Manager/GenericPriorityQueueNode.cs b/MediaBrowser.Providers/Manager/GenericPriorityQueueNode.cs
new file mode 100644
index 000000000..e6e93e443
--- /dev/null
+++ b/MediaBrowser.Providers/Manager/GenericPriorityQueueNode.cs
@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Priority_Queue
+{
+    /// Credit: https://github.com/BlueRaja/High-Speed-Priority-Queue-for-C-Sharp
+    public class GenericPriorityQueueNode<TPriority>
+    {
+        /// <summary>
+        /// The Priority to insert this node at.  Must be set BEFORE adding a node to the queue (ideally just once, in the node's constructor).
+        /// Should not be manually edited once the node has been enqueued - use queue.UpdatePriority() instead
+        /// </summary>
+        public TPriority Priority { get; protected internal set; }
+
+        /// <summary>
+        /// Represents the current position in the queue
+        /// </summary>
+        public int QueueIndex { get; internal set; }
+
+        /// <summary>
+        /// Represents the order the node was inserted in
+        /// </summary>
+        public long InsertionIndex { get; internal set; }
+    }
+}
diff --git a/MediaBrowser.Providers/Manager/IFixedSizePriorityQueue.cs b/MediaBrowser.Providers/Manager/IFixedSizePriorityQueue.cs
new file mode 100644
index 000000000..8da88e1c6
--- /dev/null
+++ b/MediaBrowser.Providers/Manager/IFixedSizePriorityQueue.cs
@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Priority_Queue
+{
+    /// <summary>
+    /// Credit: https://github.com/BlueRaja/High-Speed-Priority-Queue-for-C-Sharp
+    /// A helper-interface only needed to make writing unit tests a bit easier (hence the 'internal' access modifier)
+    /// </summary>
+    internal interface IFixedSizePriorityQueue<TItem, in TPriority> : IPriorityQueue<TItem, TPriority>
+        where TPriority : IComparable<TPriority>
+    {
+        /// <summary>
+        /// Resize the queue so it can accept more nodes.  All currently enqueued nodes are remain.
+        /// Attempting to decrease the queue size to a size too small to hold the existing nodes results in undefined behavior
+        /// </summary>
+        void Resize(int maxNodes);
+
+        /// <summary>
+        /// Returns the maximum number of items that can be enqueued at once in this queue.  Once you hit this number (ie. once Count == MaxSize),
+        /// attempting to enqueue another item will cause undefined behavior.
+        /// </summary>
+        int MaxSize { get; }
+    }
+}
\ No newline at end of file
diff --git a/MediaBrowser.Providers/Manager/IPriorityQueue.cs b/MediaBrowser.Providers/Manager/IPriorityQueue.cs
new file mode 100644
index 000000000..11f2c6214
--- /dev/null
+++ b/MediaBrowser.Providers/Manager/IPriorityQueue.cs
@@ -0,0 +1,59 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Priority_Queue
+{
+    /// <summary>
+    /// Credit: https://github.com/BlueRaja/High-Speed-Priority-Queue-for-C-Sharp
+    /// The IPriorityQueue interface.  This is mainly here for purists, and in case I decide to add more implementations later.
+    /// For speed purposes, it is actually recommended that you *don't* access the priority queue through this interface, since the JIT can
+    /// (theoretically?) optimize method calls from concrete-types slightly better.
+    /// </summary>
+    public interface IPriorityQueue<TItem, in TPriority> : IEnumerable<TItem>
+        where TPriority : IComparable<TPriority>
+    {
+        /// <summary>
+        /// Enqueue a node to the priority queue.  Lower values are placed in front. Ties are broken by first-in-first-out.
+        /// See implementation for how duplicates are handled.
+        /// </summary>
+        void Enqueue(TItem node, TPriority priority);
+
+        /// <summary>
+        /// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
+        /// </summary>
+        TItem Dequeue();
+
+        /// <summary>
+        /// Removes every node from the queue.
+        /// </summary>
+        void Clear();
+
+        /// <summary>
+        /// Returns whether the given node is in the queue.
+        /// </summary>
+        bool Contains(TItem node);
+
+        /// <summary>
+        /// Removes a node from the queue.  The node does not need to be the head of the queue.  
+        /// </summary>
+        void Remove(TItem node);
+
+        /// <summary>
+        /// Call this method to change the priority of a node.  
+        /// </summary>
+        void UpdatePriority(TItem node, TPriority priority);
+
+        /// <summary>
+        /// Returns the head of the queue, without removing it (use Dequeue() for that).
+        /// </summary>
+        TItem First { get; }
+
+        /// <summary>
+        /// Returns the number of nodes in the queue.
+        /// </summary>
+        int Count { get; }
+    }
+}
diff --git a/MediaBrowser.Providers/Manager/ProviderManager.cs b/MediaBrowser.Providers/Manager/ProviderManager.cs
index 0b8dca2eb..f08a7d3c3 100644
--- a/MediaBrowser.Providers/Manager/ProviderManager.cs
+++ b/MediaBrowser.Providers/Manager/ProviderManager.cs
@@ -24,6 +24,7 @@ using MediaBrowser.Common.IO;
 using MediaBrowser.Controller.IO;
 using MediaBrowser.Model.IO;
 using MediaBrowser.Model.Serialization;
+using Priority_Queue;
 
 namespace MediaBrowser.Providers.Manager
 {
@@ -577,7 +578,6 @@ namespace MediaBrowser.Providers.Manager
             return SaveMetadata(item, updateType, _savers.Where(i => savers.Contains(i.Name, StringComparer.OrdinalIgnoreCase)));
         }
 
-        private readonly SemaphoreSlim _saveLock = new SemaphoreSlim(1, 1);
         /// <summary>
         /// Saves the metadata.
         /// </summary>
@@ -607,8 +607,6 @@ namespace MediaBrowser.Providers.Manager
                         continue;
                     }
 
-                    await _saveLock.WaitAsync().ConfigureAwait(false);
-
                     try
                     {
                         _libraryMonitor.ReportFileSystemChangeBeginning(path);
@@ -620,7 +618,6 @@ namespace MediaBrowser.Providers.Manager
                     }
                     finally
                     {
-                        _saveLock.Release();
                         _libraryMonitor.ReportFileSystemChangeComplete(path, false);
                     }
                 }
@@ -851,20 +848,20 @@ namespace MediaBrowser.Providers.Manager
                 });
         }
 
-        private readonly ConcurrentQueue<Tuple<Guid, MetadataRefreshOptions>> _refreshQueue =
-            new ConcurrentQueue<Tuple<Guid, MetadataRefreshOptions>>();
+        private readonly SimplePriorityQueue<Tuple<Guid, MetadataRefreshOptions>> _refreshQueue =
+            new SimplePriorityQueue<Tuple<Guid, MetadataRefreshOptions>>();
 
         private readonly object _refreshQueueLock = new object();
         private bool _isProcessingRefreshQueue;
 
-        public void QueueRefresh(Guid id, MetadataRefreshOptions options)
+        public void QueueRefresh(Guid id, MetadataRefreshOptions options, RefreshPriority priority)
         {
             if (_disposed)
             {
                 return;
             }
 
-            _refreshQueue.Enqueue(new Tuple<Guid, MetadataRefreshOptions>(id, options));
+            _refreshQueue.Enqueue(new Tuple<Guid, MetadataRefreshOptions>(id, options), (int)priority);
 
             lock (_refreshQueueLock)
             {
@@ -876,12 +873,19 @@ namespace MediaBrowser.Providers.Manager
             }
         }
 
+        private bool TryDequeue(out Tuple<Guid, MetadataRefreshOptions> item)
+        {
+            item = _refreshQueue.Dequeue();
+
+            return item != null;
+        }
+
         private async Task StartProcessingRefreshQueue()
         {
             Tuple<Guid, MetadataRefreshOptions> refreshItem;
             var libraryManager = _libraryManagerFactory();
 
-            while (_refreshQueue.TryDequeue(out refreshItem))
+            while (TryDequeue(out refreshItem))
             {
                 if (_disposed)
                 {
diff --git a/MediaBrowser.Providers/Manager/SimplePriorityQueue.cs b/MediaBrowser.Providers/Manager/SimplePriorityQueue.cs
new file mode 100644
index 000000000..6435aa06b
--- /dev/null
+++ b/MediaBrowser.Providers/Manager/SimplePriorityQueue.cs
@@ -0,0 +1,243 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Priority_Queue
+{
+    /// <summary>
+    /// Credit: https://github.com/BlueRaja/High-Speed-Priority-Queue-for-C-Sharp
+    /// A simplified priority queue implementation.  Is stable, auto-resizes, and thread-safe, at the cost of being slightly slower than
+    /// FastPriorityQueue
+    /// </summary>
+    /// <typeparam name="TItem">The type to enqueue</typeparam>
+    /// <typeparam name="TPriority">The priority-type to use for nodes.  Must extend IComparable&lt;TPriority&gt;</typeparam>
+    public class SimplePriorityQueue<TItem, TPriority> : IPriorityQueue<TItem, TPriority>
+        where TPriority : IComparable<TPriority>
+    {
+        private class SimpleNode : GenericPriorityQueueNode<TPriority>
+        {
+            public TItem Data { get; private set; }
+
+            public SimpleNode(TItem data)
+            {
+                Data = data;
+            }
+        }
+
+        private const int INITIAL_QUEUE_SIZE = 10;
+        private readonly GenericPriorityQueue<SimpleNode, TPriority> _queue;
+
+        public SimplePriorityQueue()
+        {
+            _queue = new GenericPriorityQueue<SimpleNode, TPriority>(INITIAL_QUEUE_SIZE);
+        }
+
+        /// <summary>
+        /// Given an item of type T, returns the exist SimpleNode in the queue
+        /// </summary>
+        private SimpleNode GetExistingNode(TItem item)
+        {
+            var comparer = EqualityComparer<TItem>.Default;
+            foreach (var node in _queue)
+            {
+                if (comparer.Equals(node.Data, item))
+                {
+                    return node;
+                }
+            }
+            throw new InvalidOperationException("Item cannot be found in queue: " + item);
+        }
+
+        /// <summary>
+        /// Returns the number of nodes in the queue.
+        /// O(1)
+        /// </summary>
+        public int Count
+        {
+            get
+            {
+                lock (_queue)
+                {
+                    return _queue.Count;
+                }
+            }
+        }
+
+
+        /// <summary>
+        /// Returns the head of the queue, without removing it (use Dequeue() for that).
+        /// Throws an exception when the queue is empty.
+        /// O(1)
+        /// </summary>
+        public TItem First
+        {
+            get
+            {
+                lock (_queue)
+                {
+                    if (_queue.Count <= 0)
+                    {
+                        throw new InvalidOperationException("Cannot call .First on an empty queue");
+                    }
+
+                    SimpleNode first = _queue.First;
+                    return (first != null ? first.Data : default(TItem));
+                }
+            }
+        }
+
+        /// <summary>
+        /// Removes every node from the queue.
+        /// O(n)
+        /// </summary>
+        public void Clear()
+        {
+            lock (_queue)
+            {
+                _queue.Clear();
+            }
+        }
+
+        /// <summary>
+        /// Returns whether the given item is in the queue.
+        /// O(n)
+        /// </summary>
+        public bool Contains(TItem item)
+        {
+            lock (_queue)
+            {
+                var comparer = EqualityComparer<TItem>.Default;
+                foreach (var node in _queue)
+                {
+                    if (comparer.Equals(node.Data, item))
+                    {
+                        return true;
+                    }
+                }
+                return false;
+            }
+        }
+
+        /// <summary>
+        /// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
+        /// If queue is empty, throws an exception
+        /// O(log n)
+        /// </summary>
+        public TItem Dequeue()
+        {
+            lock (_queue)
+            {
+                if (_queue.Count <= 0)
+                {
+                    throw new InvalidOperationException("Cannot call Dequeue() on an empty queue");
+                }
+
+                SimpleNode node = _queue.Dequeue();
+                return node.Data;
+            }
+        }
+
+        /// <summary>
+        /// Enqueue a node to the priority queue.  Lower values are placed in front. Ties are broken by first-in-first-out.
+        /// This queue automatically resizes itself, so there's no concern of the queue becoming 'full'.
+        /// Duplicates are allowed.
+        /// O(log n)
+        /// </summary>
+        public void Enqueue(TItem item, TPriority priority)
+        {
+            lock (_queue)
+            {
+                SimpleNode node = new SimpleNode(item);
+                if (_queue.Count == _queue.MaxSize)
+                {
+                    _queue.Resize(_queue.MaxSize * 2 + 1);
+                }
+                _queue.Enqueue(node, priority);
+            }
+        }
+
+        /// <summary>
+        /// Removes an item from the queue.  The item does not need to be the head of the queue.  
+        /// If the item is not in the queue, an exception is thrown.  If unsure, check Contains() first.
+        /// If multiple copies of the item are enqueued, only the first one is removed. 
+        /// O(n)
+        /// </summary>
+        public void Remove(TItem item)
+        {
+            lock (_queue)
+            {
+                try
+                {
+                    _queue.Remove(GetExistingNode(item));
+                }
+                catch (InvalidOperationException ex)
+                {
+                    throw new InvalidOperationException("Cannot call Remove() on a node which is not enqueued: " + item, ex);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Call this method to change the priority of an item.
+        /// Calling this method on a item not in the queue will throw an exception.
+        /// If the item is enqueued multiple times, only the first one will be updated.
+        /// (If your requirements are complex enough that you need to enqueue the same item multiple times <i>and</i> be able
+        /// to update all of them, please wrap your items in a wrapper class so they can be distinguished).
+        /// O(n)
+        /// </summary>
+        public void UpdatePriority(TItem item, TPriority priority)
+        {
+            lock (_queue)
+            {
+                try
+                {
+                    SimpleNode updateMe = GetExistingNode(item);
+                    _queue.UpdatePriority(updateMe, priority);
+                }
+                catch (InvalidOperationException ex)
+                {
+                    throw new InvalidOperationException("Cannot call UpdatePriority() on a node which is not enqueued: " + item, ex);
+                }
+            }
+        }
+
+        public IEnumerator<TItem> GetEnumerator()
+        {
+            List<TItem> queueData = new List<TItem>();
+            lock (_queue)
+            {
+                //Copy to a separate list because we don't want to 'yield return' inside a lock
+                foreach (var node in _queue)
+                {
+                    queueData.Add(node.Data);
+                }
+            }
+
+            return queueData.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        public bool IsValidQueue()
+        {
+            lock (_queue)
+            {
+                return _queue.IsValidQueue();
+            }
+        }
+    }
+
+    /// <summary>
+    /// A simplified priority queue implementation.  Is stable, auto-resizes, and thread-safe, at the cost of being slightly slower than
+    /// FastPriorityQueue
+    /// This class is kept here for backwards compatibility.  It's recommended you use Simple
+    /// </summary>
+    /// <typeparam name="TItem">The type to enqueue</typeparam>
+    public class SimplePriorityQueue<TItem> : SimplePriorityQueue<TItem, float> { }
+}
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