Upgrade locker

Former-commit-id: 0e2625d0d4ef02589ab13f9298e649be41dcd334
Former-commit-id: a45e1898fff0dbdf3b4620611d1276e5c038c8e6
Former-commit-id: 27f90127fab95af155788f8fdfb04fb35ba193cc

src/ImageProcessor.Web/Caching/MemCache.cs

@@ -14,6 +14,9 @@ namespace ImageProcessor.Web.Caching
     using System.Collections.Concurrent;
     using System.Collections.Generic;
     using System.Runtime.Caching;
+    using System.Threading;
+
+    using ImageProcessor.Common.Helpers;
 
     /// <summary>
     /// Encapsulates methods that allow the caching and retrieval of objects from the in memory cache.
@@ -25,6 +28,11 @@ namespace ImageProcessor.Web.Caching
         /// </summary>
         private static readonly ObjectCache Cache = MemoryCache.Default;
 
+        /// <summary>
+        /// The reader-writer lock implementation.
+        /// </summary>
+        private static readonly ReaderWriterLockSlim Locker = new ReaderWriterLockSlim();
+
         /// <summary>
         /// An internal list of cache keys to allow bulk removal.
         /// </summary>
@@ -56,8 +64,7 @@ namespace ImageProcessor.Web.Caching
         public static bool AddItem(string key, object value, CacheItemPolicy policy = null, string regionName = null)
         {
             bool isAdded;
-
-            lock (Cache)
+            using (new WriteLock(Locker))
             {
                 if (policy == null)
                 {
@@ -100,7 +107,7 @@ namespace ImageProcessor.Web.Caching
         /// </returns>
         public static object GetItem(string key, string regionName = null)
         {
-            lock (Cache)
+            using (new UpgradeableReadLock(Locker))
             {
                 return Cache.Get(key, regionName);
             }
@@ -173,7 +180,7 @@ namespace ImageProcessor.Web.Caching
         {
             bool isRemoved;
 
-            lock (Cache)
+            using (new WriteLock(Locker))
             {
                 isRemoved = Cache.Remove(key, regionName) != null;
 
@@ -200,7 +207,7 @@ namespace ImageProcessor.Web.Caching
         {
             bool isCleared = false;
 
-            lock (CacheItems)
+            using (new WriteLock(Locker))
             {
                 // You can't remove items from a collection whilst you are iterating over it so you need to 
                 // create a collection to store the items to remove.