added new in memory cache.

NzbDrone.Common/Cache/Cached.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Concurrent;
+using NzbDrone.Common.EnsureThat;
+
+namespace NzbDrone.Common.Cache
+{
+    public class Cached<T> : ICached<T>
+    {
+        private readonly ConcurrentDictionary<string, T> _store;
+
+        public Cached()
+        {
+            _store = new ConcurrentDictionary<string, T>();
+        }
+
+        public void Set(string key, T value)
+        {
+            Ensure.That(() => key).IsNotNullOrWhiteSpace();
+            _store.TryAdd(key, value);
+        }
+
+        public T Get(string key, Func<T> function)
+        {
+            Ensure.That(() => key).IsNotNullOrWhiteSpace();
+
+            T value;
+
+            if (!_store.TryGetValue(key, out value))
+            {
+                value = function();
+                Set(key, value);
+            }
+
+            return value;
+        }
+
+        public bool ContainsKey(string key)
+        {
+            Ensure.That(() => key).IsNotNullOrWhiteSpace();
+            return _store.ContainsKey(key);
+        }
+
+        public void Clear()
+        {
+            _store.Clear();
+        }
+
+        public void Remove(string key)
+        {
+            Ensure.That(() => key).IsNotNullOrWhiteSpace();
+            T value;
+            _store.TryRemove(key, out value);
+        }
+    }
+}