Fixing threading issue?

Former-commit-id: 9dfcb11ad66196f32d3b1d13777e77862ac7fd67

src/ImageProcessor.Web/NET45/HttpModules/ImageProcessingModule.cs

@@ -157,12 +157,11 @@ namespace ImageProcessor.Web.HttpModules
         /// The id representing the <see cref="T:System.Threading.SemaphoreSlim"/>.
         /// </param>
         /// <returns>
-        /// The <see cref="T:System.Threading.Mutex"/> for the given id.
+        /// The <see cref="T:System.Threading.SemaphoreSlim"/> for the given id.
         /// </returns>
         private static SemaphoreSlim GetSemaphoreSlim(string id)
         {
-            SemaphoreSlim semaphore = SemaphoreSlims.GetOrAdd(id, new SemaphoreSlim(1, 1));
+            return SemaphoreSlims.GetOrAdd(id, new SemaphoreSlim(1, 1));
-            return semaphore;
         }
 
         /// <summary>
@@ -385,6 +384,15 @@ namespace ImageProcessor.Web.HttpModules
                         {
                             if (isRemote)
                             {
+                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
+                                try
+                                {
+                                    // This should not happen :(  
+                                    if (semaphore != null)
+                                    {
+                                        semaphore.Wait();
+                                    }
+
                                     Uri uri = new Uri(requestPath + "?" + urlParameters);
 
                                     RemoteFile remoteFile = new RemoteFile(uri, false);
@@ -392,11 +400,6 @@ namespace ImageProcessor.Web.HttpModules
                                     // Prevent response blocking.
                                     WebResponse webResponse = await remoteFile.GetWebResponseAsync().ConfigureAwait(false);
 
-                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
-                                try
-                                {
-                                    semaphore.Wait();
-
                                     using (MemoryStream memoryStream = new MemoryStream())
                                     {
                                         using (WebResponse response = webResponse)
@@ -429,12 +432,25 @@ namespace ImageProcessor.Web.HttpModules
                                     }
                                 }
                                 finally
+                                {
+                                    // This should not happen :(  
+                                    if (semaphore != null)
                                     {
                                         semaphore.Release();
                                     }
                                 }
+                            }
                             else
                             {
+                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
+                                try
+                                {
+                                    // This should not happen :(  
+                                    if (semaphore != null)
+                                    {
+                                        semaphore.Wait();
+                                    }
+
                                     // Check to see if the file exists.
                                     // ReSharper disable once AssignNullToNotNullAttribute
                                     FileInfo fileInfo = new FileInfo(requestPath);
@@ -444,11 +460,6 @@ namespace ImageProcessor.Web.HttpModules
                                         throw new HttpException(404, "No image exists at " + fullPath);
                                     }
 
-                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
-                                try
-                                {
-                                    semaphore.Wait();
-
                                     // Process the Image
                                     imageFactory.Load(requestPath)
                                                 .AutoProcess(queryString)
@@ -464,12 +475,16 @@ namespace ImageProcessor.Web.HttpModules
                                     await cache.TrimCachedFolderAsync(cachedPath);
                                 }
                                 finally
+                                {
+                                    // This should not happen :(  
+                                    if (semaphore != null)
                                     {
                                         semaphore.Release();
                                     }
                                 }
                             }
                         }
+                    }
 
                     string incomingEtag = context.Request.Headers["If-None-Match"];