imported signalr 1.1.3 into NzbDrone.

src/Microsoft.AspNet.SignalR.Core/Infrastructure/SafeSet.cs

@@ -0,0 +1,60 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.md in the project root for license information.
+
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.AspNet.SignalR.Infrastructure
+{
+    internal class SafeSet<T>
+    {
+        private readonly ConcurrentDictionary<T, object> _items;
+
+        public SafeSet()
+        {
+            _items = new ConcurrentDictionary<T, object>();
+        }
+
+        public SafeSet(IEqualityComparer<T> comparer)
+        {
+            _items = new ConcurrentDictionary<T, object>(comparer);
+        }
+
+        public SafeSet(IEnumerable<T> items)
+        {
+            _items = new ConcurrentDictionary<T, object>(items.Select(x => new KeyValuePair<T, object>(x, null)));
+        }
+
+        public ICollection<T> GetSnapshot()
+        {
+            // The Keys property locks, so Select instead
+            return _items.Keys;
+        }
+
+        public bool Contains(T item)
+        {
+            return _items.ContainsKey(item);
+        }
+
+        public bool Add(T item)
+        {
+            return _items.TryAdd(item, null);
+        }
+
+        public bool Remove(T item)
+        {
+            object _;
+            return _items.TryRemove(item, out _);
+        }
+
+        public bool Any()
+        {
+            return _items.Any();
+        }
+
+        public long Count
+        {
+            get { return _items.Count; }
+        }
+    }
+}