Adding AsyncDeDuper

Former-commit-id: 30973a9ce646ad5301c4c68fbd66ddb2d37b8f29

src/ImageProcessor.Web/NET4/ImageProcessor.Web_NET4.csproj

@@ -101,6 +101,9 @@
     <Compile Include="..\NET45\Extensions\StringExtensions.cs">
       <Link>StringExtensions.cs</Link>
     </Compile>
+    <Compile Include="..\NET45\Helpers\AsyncDeDuperLock.cs">
+      <Link>AsyncDeDuperLock.cs</Link>
+    </Compile>
     <Compile Include="..\NET45\Helpers\CommonParameterParserUtility.cs">
       <Link>CommonParameterParserUtility.cs</Link>
     </Compile>

src/ImageProcessor.Web/NET45/Helpers/AsyncDeDuperLock.cs

@@ -0,0 +1,134 @@
+// --------------------------------------------------------------------------------------------------------------------
+// <copyright file="AsyncDeDuperLock.cs" company="James South">
+//   Copyright (c) James South.
+//   Licensed under the Apache License, Version 2.0.
+// </copyright>
+// <summary>
+//   Throttles duplicate requests.
+// </summary>
+// --------------------------------------------------------------------------------------------------------------------
+namespace ImageProcessor.Web.Helpers
+{
+    using System;
+    using System.Collections.Concurrent;
+    using System.Threading;
+    using System.Threading.Tasks;
+
+    /// <summary>
+    /// Throttles duplicate requests.
+    /// Based loosely on <see href="http://stackoverflow.com/a/21011273/427899"/>
+    /// </summary>
+    public sealed class AsyncDeDuperLock
+    {
+        /// <summary>
+        /// The semaphore slims.
+        /// </summary>
+        private static readonly ConcurrentDictionary<string, SemaphoreSlim> SemaphoreSlims = new ConcurrentDictionary<string, SemaphoreSlim>();
+
+        /// <summary>
+        /// The lock.
+        /// </summary>
+        /// <param name="key">
+        /// The hash.
+        /// </param>
+        /// <returns>
+        /// The <see cref="IDisposable"/>.
+        /// </returns>
+        public IDisposable Lock(string key)
+        {
+            DisposableScope releaser = new DisposableScope(
+            key,
+            s =>
+            {
+                SemaphoreSlim locker;
+                if (SemaphoreSlims.TryRemove(s, out locker))
+                {
+                    locker.Release();
+                    locker.Dispose();
+                }
+            });
+
+            SemaphoreSlim semaphore = SemaphoreSlims.GetOrAdd(key, new SemaphoreSlim(1, 1));
+            semaphore.Wait();
+            return releaser;
+        }
+
+#if NET45 && !__MonoCS__
+        /// <summary>
+        /// The lock async.
+        /// </summary>
+        /// <param name="key">
+        /// The key.
+        /// </param>
+        /// <returns>
+        /// The <see cref="Task"/>.
+        /// </returns>
+        public Task<IDisposable> LockAsync(string key)
+        {
+            DisposableScope releaser = new DisposableScope(
+            key,
+            s =>
+            {
+                SemaphoreSlim locker;
+                if (SemaphoreSlims.TryRemove(s, out locker))
+                {
+                    locker.Release();
+                    locker.Dispose();
+                }
+            });
+
+            Task<IDisposable> releaserTask = Task.FromResult(releaser as IDisposable);
+            SemaphoreSlim semaphore = SemaphoreSlims.GetOrAdd(key, new SemaphoreSlim(1, 1));
+            
+            Task waitTask = semaphore.WaitAsync();
+
+            return waitTask.IsCompleted
+                       ? releaserTask
+                       : waitTask.ContinueWith(
+                           (_, r) => (IDisposable)r,
+                           releaser,
+                           CancellationToken.None,
+                           TaskContinuationOptions.ExecuteSynchronously,
+                           TaskScheduler.Default);
+        }
+#endif
+        /// <summary>
+        /// The disposable scope.
+        /// </summary>
+        internal sealed class DisposableScope : IDisposable
+        {
+            /// <summary>
+            /// The key
+            /// </summary>
+            private readonly string key;
+
+            /// <summary>
+            /// The close scope action.
+            /// </summary>
+            private readonly Action<string> closeScopeAction;
+
+            /// <summary>
+            /// Initializes a new instance of the <see cref="DisposableScope"/> class.
+            /// </summary>
+            /// <param name="key">
+            /// The key.
+            /// </param>
+            /// <param name="closeScopeAction">
+            /// The close scope action.
+            /// </param>
+            public DisposableScope(string key, Action<string> closeScopeAction)
+            {
+                this.key = key;
+                this.closeScopeAction = closeScopeAction;
+            }
+
+            /// <summary>
+            /// The dispose.
+            /// </summary>
+            public void Dispose()
+            {
+                this.closeScopeAction(this.key);
+            }
+        }
+    }
+}

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

@@ -12,7 +12,6 @@ namespace ImageProcessor.Web.HttpModules
 {
     #region Using
     using System;
-    using System.Collections.Concurrent;
     using System.Diagnostics.CodeAnalysis;
     using System.IO;
     using System.Linq;
@@ -22,7 +21,6 @@ namespace ImageProcessor.Web.HttpModules
     using System.Security.Permissions;
     using System.Security.Principal;
     using System.Text.RegularExpressions;
-    using System.Threading;
     using System.Threading.Tasks;
     using System.Web;
     using System.Web.Hosting;
@@ -56,9 +54,9 @@ namespace ImageProcessor.Web.HttpModules
         private static readonly string AssemblyVersion = Assembly.GetExecutingAssembly().GetName().Version.ToString();
 
         /// <summary>
-        /// The collection of SemaphoreSlims for identifying given locking individual queries.
+        /// The locker for preventing duplicate requests.
         /// </summary>
-        private static readonly ConcurrentDictionary<string, SemaphoreSlim> SemaphoreSlims = new ConcurrentDictionary<string, SemaphoreSlim>();
+        private static readonly AsyncDeDuperLock Locker = new AsyncDeDuperLock();
 
         /// <summary>
         /// The value to prefix any remote image requests with to ensure they get captured.
@@ -149,20 +147,6 @@ namespace ImageProcessor.Web.HttpModules
             GC.SuppressFinalize(this);
         }
 
-        /// <summary>
-        /// Gets the specific <see cref="T:System.Threading.SemaphoreSlim"/> for the given id.
-        /// </summary>
-        /// <param name="id">
-        /// The id representing the <see cref="T:System.Threading.SemaphoreSlim"/>.
-        /// </param>
-        /// <returns>
-        /// The <see cref="T:System.Threading.SemaphoreSlim"/> for the given id.
-        /// </returns>
-        private static SemaphoreSlim GetSemaphoreSlim(string id)
-        {
-            return SemaphoreSlims.GetOrAdd(id, new SemaphoreSlim(1, 1));
-        }
-
         /// <summary>
         /// Disposes the object and frees resources for the Garbage Collector.
         /// </summary>
@@ -377,13 +361,11 @@ namespace ImageProcessor.Web.HttpModules
                         {
                             if (isRemote)
                             {
-                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
 #if NET45 && !__MonoCS__
-                                await semaphore.WaitAsync();
+                                using (await Locker.LockAsync(cachedPath))
 #else
-                                semaphore.Wait();
+                                using (Locker.Lock(cachedPath))
 #endif
-                                try
                                 {
                                     Uri uri = new Uri(requestPath + "?" + urlParameters);
                                     RemoteFile remoteFile = new RemoteFile(uri, false);
@@ -422,20 +404,14 @@ namespace ImageProcessor.Web.HttpModules
                                         }
                                     }
                                 }
-                                finally
-                                {
-                                    semaphore.Release();
-                                }
                             }
                             else
                             {
-                                SemaphoreSlim semaphore = GetSemaphoreSlim(cachedPath);
 #if NET45 && !__MonoCS__
-                                await semaphore.WaitAsync();
+                                using (await Locker.LockAsync(cachedPath))
 #else
-                                semaphore.Wait();
+                                using (Locker.Lock(cachedPath))
 #endif
-                                try
                                 {
                                     // Check to see if the file exists.
                                     // ReSharper disable once AssignNullToNotNullAttribute
@@ -460,10 +436,6 @@ namespace ImageProcessor.Web.HttpModules
                                     // Trim the cache.
                                     await cache.TrimCachedFolderAsync(cachedPath);
                                 }
-                                finally
-                                {
-                                    semaphore.Release();
-                                }
                             }
                         }
                     }

src/ImageProcessor.Web/NET45/ImageProcessor.Web_NET45.csproj

@@ -56,6 +56,7 @@
     <Compile Include="Extensions\DirectoryInfoExtensions.cs" />
     <Compile Include="Extensions\StringExtensions.cs" />
     <Compile Include="Helpers\CommonParameterParserUtility.cs" />
+    <Compile Include="Helpers\AsyncDeDuperLock.cs" />
     <Compile Include="Helpers\NativeMethods.cs" />
     <Compile Include="Helpers\ResourceHelpers.cs" />
     <Compile Include="Helpers\ImageHelpers.cs" />