Don't invoke async state machine unnecessarily

Return task rather than awaiting when no extra work needs to be done
after await

src/Microsoft.AspNet.Mvc.Core/AuthorizationFilterAttribute.cs

@@ -14,12 +14,11 @@ namespace Microsoft.AspNet.Mvc
     {
         public int Order { get; set; }
 
-#pragma warning disable 1998
+        public virtual Task OnAuthorizationAsync([NotNull] AuthorizationContext context)
-        public virtual async Task OnAuthorizationAsync([NotNull] AuthorizationContext context)
         {
             OnAuthorization(context);
+            return TaskCache.CompletedTask;
         }
-#pragma warning restore 1998
 
         public virtual void OnAuthorization([NotNull] AuthorizationContext context)
         {

src/Microsoft.AspNet.Mvc.Core/ContentResult.cs

@@ -31,7 +31,7 @@ namespace Microsoft.AspNet.Mvc
         /// </summary>
         public int? StatusCode { get; set; }
 
-        public override async Task ExecuteResultAsync([NotNull] ActionContext context)
+        public override Task ExecuteResultAsync([NotNull] ActionContext context)
         {
             var response = context.HttpContext.Response;
             var contentTypeHeader = ContentType;
@@ -54,8 +54,9 @@ namespace Microsoft.AspNet.Mvc
 
             if (Content != null)
             {
-                await response.WriteAsync(Content, contentTypeHeader?.Encoding ?? DefaultContentType.Encoding);
+                return response.WriteAsync(Content, contentTypeHeader?.Encoding ?? DefaultContentType.Encoding);
             }
+            return TaskCache.CompletedTask;
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/ControllerActionExecutor.cs

@@ -25,16 +25,16 @@ namespace Microsoft.AspNet.Mvc
             return CastToObject<T>(task);
         }
 
-        public static async Task<object> ExecuteAsync(
+        public static Task<object> ExecuteAsync(
             MethodInfo actionMethodInfo,
             object instance,
             IDictionary<string, object> actionArguments)
         {
             var orderedArguments = PrepareArguments(actionArguments, actionMethodInfo.GetParameters());
-            return await ExecuteAsync(actionMethodInfo, instance, orderedArguments);
+            return ExecuteAsync(actionMethodInfo, instance, orderedArguments);
         }
 
-        public static async Task<object> ExecuteAsync(
+        public static Task<object> ExecuteAsync(
             MethodInfo actionMethodInfo,
             object instance,
             object[] orderedActionArguments)
@@ -51,7 +51,7 @@ namespace Microsoft.AspNet.Mvc
                 exceptionDispatchInfo.Throw();
             }
 
-            return await CoerceResultToTaskAsync(
+            return CoerceResultToTaskAsync(
                 invocationResult,
                 actionMethodInfo.ReturnType,
                 actionMethodInfo.Name,

src/Microsoft.AspNet.Mvc.Core/ExceptionFilterAttribute.cs

@@ -12,12 +12,11 @@ namespace Microsoft.AspNet.Mvc
     {
         public int Order { get; set; }
 
-#pragma warning disable 1998
+        public virtual Task OnExceptionAsync([NotNull] ExceptionContext context)
-        public virtual async Task OnExceptionAsync([NotNull] ExceptionContext context)
         {
             OnException(context);
+            return TaskCache.CompletedTask;
         }
-#pragma warning restore 1998
 
         public virtual void OnException([NotNull] ExceptionContext context)
         {

src/Microsoft.AspNet.Mvc.Core/FilterActionInvoker.cs

@@ -186,12 +186,12 @@ namespace Microsoft.AspNet.Mvc.Core
             return context.Results.Select(item => item.Filter).Where(filter => filter != null).ToArray();
         }
 
-        private async Task InvokeAllAuthorizationFiltersAsync()
+        private Task InvokeAllAuthorizationFiltersAsync()
         {
             _cursor.SetStage(FilterStage.AuthorizationFilters);
 
             _authorizationContext = new AuthorizationContext(ActionContext, _filters);
-            await InvokeAuthorizationFilterAsync();
+            return InvokeAuthorizationFilterAsync();
         }
 
         private async Task InvokeAuthorizationFilterAsync()
@@ -236,7 +236,7 @@ namespace Microsoft.AspNet.Mvc.Core
             }
         }
 
-        private async Task InvokeAllResourceFiltersAsync()
+        private Task InvokeAllResourceFiltersAsync()
         {
             _cursor.SetStage(FilterStage.ResourceFilters);
 
@@ -249,7 +249,7 @@ namespace Microsoft.AspNet.Mvc.Core
             context.ValueProviderFactories = new CopyOnWriteList<IValueProviderFactory>(_valueProviderFactories);
 
             _resourceExecutingContext = context;
-            await InvokeResourceFilterAsync();
+            return InvokeResourceFilterAsync();
         }
 
         private async Task<ResourceExecutedContext> InvokeResourceFilterAsync()
@@ -397,11 +397,11 @@ namespace Microsoft.AspNet.Mvc.Core
             return _resourceExecutedContext;
         }
 
-        private async Task InvokeAllExceptionFiltersAsync()
+        private Task InvokeAllExceptionFiltersAsync()
         {
             _cursor.SetStage(FilterStage.ExceptionFilters);
 
-            await InvokeExceptionFilterAsync();
+            return InvokeExceptionFilterAsync();
         }
 
         private async Task InvokeExceptionFilterAsync()
@@ -654,24 +654,9 @@ namespace Microsoft.AspNet.Mvc.Core
                 {
                     await item.FilterAsync.OnResultExecutionAsync(_resultExecutingContext, InvokeResultFilterAsync);
 
-                    if (_resultExecutedContext == null)
+                    if (_resultExecutedContext == null || _resultExecutingContext.Cancel == true)
                     {
-                        // Short-circuited by not calling next
+                        // Short-circuited by not calling next || Short-circuited by setting Cancel == true
-
-                        _logger.LogVerbose(ResourceFilterShortCircuitLogMessage, item.FilterAsync.GetType().FullName);
-
-                        _resultExecutedContext = new ResultExecutedContext(
-                            _resultExecutingContext,
-                            _filters,
-                            _resultExecutingContext.Result,
-                            Instance)
-                        {
-                            Canceled = true,
-                        };
-                    }
-                    else if (_resultExecutingContext.Cancel == true)
-                    {
-                        // Short-circuited by setting Cancel == true
 
                         _logger.LogVerbose(ResourceFilterShortCircuitLogMessage, item.FilterAsync.GetType().FullName);
 

src/Microsoft.AspNet.Mvc.Core/HttpResponseStreamWriter.cs

@@ -146,9 +146,9 @@ namespace Microsoft.AspNet.Mvc
             FlushInternal(true, true);
         }
 
-        public override async Task FlushAsync()
+        public override Task FlushAsync()
         {
-            await FlushInternalAsync(true, true);
+            return FlushInternalAsync(flushStream: true, flushEncoder: true);
         }
 
         // Do not flush the stream on Dispose, as this will cause response to be

src/Microsoft.AspNet.Mvc.Core/InputFormatter.cs

@@ -82,15 +82,15 @@ namespace Microsoft.AspNet.Mvc
         }
 
         /// <inheritdoc />
-        public virtual async Task<object> ReadAsync(InputFormatterContext context)
+        public virtual Task<object> ReadAsync(InputFormatterContext context)
         {
             var request = context.HttpContext.Request;
             if (request.ContentLength == 0)
             {
-                return GetDefaultValueForType(context.ModelType);
+                return Task.FromResult(GetDefaultValueForType(context.ModelType));
             }
 
-            return await ReadRequestBodyAsync(context);
+            return ReadRequestBodyAsync(context);
         }
 
         /// <summary>

src/Microsoft.AspNet.Mvc.Core/ModelBinding/CollectionModelBinder.cs

@@ -189,13 +189,13 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         }
 
         // Used when the ValueProvider contains the collection to be bound as multiple elements, e.g. foo[0], foo[1].
-        private async Task<CollectionResult> BindComplexCollection(ModelBindingContext bindingContext)
+        private Task<CollectionResult> BindComplexCollection(ModelBindingContext bindingContext)
         {
             var indexPropertyName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, "index");
             var valueProviderResultIndex = bindingContext.ValueProvider.GetValue(indexPropertyName);
             var indexNames = GetIndexNamesFromValueProviderResult(valueProviderResultIndex);
 
-            return await BindComplexCollectionFromIndexes(bindingContext, indexNames);
+            return BindComplexCollectionFromIndexes(bindingContext, indexNames);
         }
 
         // Internal for testing.

src/Microsoft.AspNet.Mvc.Core/MvcRouteHandler.cs

@@ -101,7 +101,7 @@ namespace Microsoft.AspNet.Mvc
             }
         }
 
-        private async Task InvokeActionAsync(RouteContext context, ActionDescriptor actionDescriptor)
+        private Task InvokeActionAsync(RouteContext context, ActionDescriptor actionDescriptor)
         {
             var actionContext = new ActionContext(context.HttpContext, context.RouteData, actionDescriptor);
             _actionContextAccessor.ActionContext = actionContext;
@@ -114,7 +114,7 @@ namespace Microsoft.AspNet.Mvc
                         actionDescriptor.DisplayName));
             }
 
-            await invoker.InvokeAsync();
+            return invoker.InvokeAsync();
         }
 
         private void EnsureServices(HttpContext context)

src/Microsoft.AspNet.Mvc.Core/ObjectResult.cs

@@ -37,7 +37,7 @@ namespace Microsoft.AspNet.Mvc
         /// </summary>
         public int? StatusCode { get; set; }
 
-        public override async Task ExecuteResultAsync(ActionContext context)
+        public override Task ExecuteResultAsync(ActionContext context)
         {
             var logger = context.HttpContext.RequestServices.GetRequiredService<ILogger<ObjectResult>>();
                             
@@ -60,7 +60,7 @@ namespace Microsoft.AspNet.Mvc
                 logger.LogWarning("No output formatter was found to write the response.");
 
                 context.HttpContext.Response.StatusCode = StatusCodes.Status406NotAcceptable;
-                return;
+                return TaskCache.CompletedTask;
             }
 
             logger.LogVerbose(
@@ -75,7 +75,7 @@ namespace Microsoft.AspNet.Mvc
             }
 
             OnFormatting(context);
-            await selectedFormatter.WriteAsync(formatterContext);
+            return selectedFormatter.WriteAsync(formatterContext);
         }
 
         public virtual IOutputFormatter SelectFormatter(

src/Microsoft.AspNet.Mvc.Core/OutputFormatter.cs

@@ -158,10 +158,10 @@ namespace Microsoft.AspNet.Mvc
         }
 
         /// <inheritdoc />
-        public async Task WriteAsync([NotNull] OutputFormatterContext context)
+        public Task WriteAsync([NotNull] OutputFormatterContext context)
         {
             WriteResponseHeaders(context);
-            await WriteResponseBodyAsync(context);
+            return WriteResponseBodyAsync(context);
         }
 
         /// <summary>

src/Microsoft.AspNet.Mvc.Core/StringOutputFormatter.cs

@@ -37,17 +37,17 @@ namespace Microsoft.AspNet.Mvc
             return false;
         }
 
-        public override async Task WriteResponseBodyAsync(OutputFormatterContext context)
+        public override Task WriteResponseBodyAsync(OutputFormatterContext context)
         {
             var valueAsString = (string)context.Object;
             if (string.IsNullOrEmpty(valueAsString))
             {
-                return;
+                return TaskCache.CompletedTask;
             }
 
             var response = context.HttpContext.Response;
 
-            await response.WriteAsync(valueAsString, context.SelectedEncoding);
+            return response.WriteAsync(valueAsString, context.SelectedEncoding);
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/TaskCache.cs

@@ -0,0 +1,29 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNet.Mvc
+{
+    public static class TaskCache
+    {
+#if DNX451
+        static readonly Task _completedTask = Task.FromResult(0);
+#endif
+
+        /// <summary>Gets a task that's already been completed successfully.</summary>
+        /// <remarks>May not always return the same instance.</remarks>        
+        public static Task CompletedTask
+        {
+            get
+            {
+#if DNX451
+                return _completedTask;
+#else
+                return Task.CompletedTask;
+#endif
+            }
+        }
+    }
+
+}

src/Microsoft.AspNet.Mvc.Cors/CorsAuthorizationFilter.cs

@@ -74,7 +74,6 @@ namespace Microsoft.AspNet.Mvc
                     // If this was a preflight, there is no need to run anything else.
                     // Also the response is always 200 so that anyone after mvc can handle the pre flight request.
                     context.Result = new HttpStatusCodeResult(StatusCodes.Status200OK);
-                    await Task.FromResult(true);
                 }
 
                 // Continue with other filters and action.

src/Microsoft.AspNet.Mvc.Razor/RazorPage.cs

@@ -294,9 +294,9 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// <returns>
         /// A <see cref="Task"/> that on completion writes the <paramref name="tagHelperExecutionContext"/> content.
         /// </returns>
-        public async Task WriteTagHelperAsync([NotNull] TagHelperExecutionContext tagHelperExecutionContext)
+        public Task WriteTagHelperAsync([NotNull] TagHelperExecutionContext tagHelperExecutionContext)
         {
-            await WriteTagHelperToAsync(Output, tagHelperExecutionContext);
+            return WriteTagHelperToAsync(Output, tagHelperExecutionContext);
         }
 
         /// <summary>
@@ -773,10 +773,10 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// value does not represent the rendered content.</remarks>
         /// <exception cref="InvalidOperationException">if <paramref name="required"/> is <c>true</c> and the section
         /// was not registered using the <c>@section</c> in the Razor page.</exception>
-        public async Task<HtmlString> RenderSectionAsync([NotNull] string name, bool required)
+        public Task<HtmlString> RenderSectionAsync([NotNull] string name, bool required)
         {
             EnsureMethodCanBeInvoked(nameof(RenderSectionAsync));
-            return await RenderSectionAsyncCore(name, required);
+            return RenderSectionAsyncCore(name, required);
         }
 
         private async Task<HtmlString> RenderSectionAsyncCore(string sectionName, bool required)

src/Microsoft.AspNet.Mvc.Razor/RazorView.cs

@@ -125,7 +125,7 @@ namespace Microsoft.AspNet.Mvc.Razor
             }
         }
 
-        private async Task RenderPageCoreAsync(IRazorPage page, ViewContext context)
+        private Task RenderPageCoreAsync(IRazorPage page, ViewContext context)
         {
             page.IsPartial = IsPartial;
             page.ViewContext = context;
@@ -135,7 +135,7 @@ namespace Microsoft.AspNet.Mvc.Razor
             }
 
             _pageActivator.Activate(page, context);
-            await page.ExecuteAsync();
+            return page.ExecuteAsync();
         }
 
         private async Task RenderViewStartAsync(ViewContext context)

src/Microsoft.AspNet.Mvc.ViewFeatures/Controller.cs

@@ -1083,7 +1083,8 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="model">The model instance to update.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public virtual Task<bool> TryUpdateModelAsync<TModel>([NotNull] TModel model)
+        public virtual Task<bool> TryUpdateModelAsync<TModel>(
+            [NotNull] TModel model)
             where TModel : class
         {
             return TryUpdateModelAsync(model, prefix: string.Empty);
@@ -1099,8 +1100,9 @@ namespace Microsoft.AspNet.Mvc
         /// </param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public virtual async Task<bool> TryUpdateModelAsync<TModel>([NotNull] TModel model,
+        public virtual Task<bool> TryUpdateModelAsync<TModel>(
-                                                                    [NotNull] string prefix)
+            [NotNull] TModel model,
+            [NotNull] string prefix)
             where TModel : class
         {
             if (BindingContext == null)
@@ -1111,7 +1113,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await TryUpdateModelAsync(model, prefix, BindingContext.ValueProvider);
+            return TryUpdateModelAsync(model, prefix, BindingContext.ValueProvider);
         }
 
         /// <summary>
@@ -1125,9 +1127,10 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="valueProvider">The <see cref="IValueProvider"/> used for looking up values.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public virtual async Task<bool> TryUpdateModelAsync<TModel>([NotNull] TModel model,
+        public virtual Task<bool> TryUpdateModelAsync<TModel>(
-                                                                    [NotNull] string prefix,
+            [NotNull] TModel model,
-                                                                    [NotNull] IValueProvider valueProvider)
+            [NotNull] string prefix,
+            [NotNull] IValueProvider valueProvider)
             where TModel : class
         {
             if (BindingContext == null)
@@ -1138,7 +1141,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 prefix,
                 ActionContext.HttpContext,
@@ -1163,7 +1166,7 @@ namespace Microsoft.AspNet.Mvc
         /// which need to be included for the current model.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public async Task<bool> TryUpdateModelAsync<TModel>(
+        public Task<bool> TryUpdateModelAsync<TModel>(
             [NotNull] TModel model,
             string prefix,
             [NotNull] params Expression<Func<TModel, object>>[] includeExpressions)
@@ -1177,7 +1180,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 prefix,
                 ActionContext.HttpContext,
@@ -1202,7 +1205,7 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="predicate">A predicate which can be used to filter properties at runtime.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public async Task<bool> TryUpdateModelAsync<TModel>(
+        public Task<bool> TryUpdateModelAsync<TModel>(
             [NotNull] TModel model,
             string prefix,
             [NotNull] Func<ModelBindingContext, string, bool> predicate)
@@ -1216,7 +1219,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 prefix,
                 ActionContext.HttpContext,
@@ -1243,7 +1246,7 @@ namespace Microsoft.AspNet.Mvc
         /// which need to be included for the current model.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public async Task<bool> TryUpdateModelAsync<TModel>(
+        public Task<bool> TryUpdateModelAsync<TModel>(
             [NotNull] TModel model,
             string prefix,
             [NotNull] IValueProvider valueProvider,
@@ -1258,7 +1261,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 prefix,
                 ActionContext.HttpContext,
@@ -1284,7 +1287,7 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="predicate">A predicate which can be used to filter properties at runtime.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public async Task<bool> TryUpdateModelAsync<TModel>(
+        public Task<bool> TryUpdateModelAsync<TModel>(
             [NotNull] TModel model,
             string prefix,
             [NotNull] IValueProvider valueProvider,
@@ -1299,7 +1302,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 prefix,
                 ActionContext.HttpContext,
@@ -1323,9 +1326,10 @@ namespace Microsoft.AspNet.Mvc
         /// </param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public virtual async Task<bool> TryUpdateModelAsync([NotNull] object model,
+        public virtual Task<bool> TryUpdateModelAsync(
-                                                            [NotNull] Type modelType,
+            [NotNull] object model,
-                                                            string prefix)
+            [NotNull] Type modelType,
+            string prefix)
         {
             if (BindingContext == null)
             {
@@ -1335,7 +1339,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 modelType,
                 prefix,
@@ -1361,7 +1365,7 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="predicate">A predicate which can be used to filter properties at runtime.</param>
         /// <returns>A <see cref="Task"/> that on completion returns <c>true</c> if the update is successful.</returns>
         [NonAction]
-        public async Task<bool> TryUpdateModelAsync(
+        public Task<bool> TryUpdateModelAsync(
             [NotNull] object model,
             [NotNull] Type modelType,
             string prefix,
@@ -1376,7 +1380,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(message);
             }
 
-            return await ModelBindingHelper.TryUpdateModelAsync(
+            return ModelBindingHelper.TryUpdateModelAsync(
                 model,
                 modelType,
                 prefix,
@@ -1397,7 +1401,8 @@ namespace Microsoft.AspNet.Mvc
         /// <param name="model">The model to validate.</param>
         /// <returns><c>true</c> if the <see cref="ModelState"/> is valid; <c>false</c> otherwise.</returns>
         [NonAction]
-        public virtual bool TryValidateModel([NotNull] object model)
+        public virtual bool TryValidateModel(
+            [NotNull] object model)
         {
             return TryValidateModel(model, prefix: null);
         }
@@ -1410,7 +1415,9 @@ namespace Microsoft.AspNet.Mvc
         /// </param>
         /// <returns><c>true</c> if the <see cref="ModelState"/> is valid;<c>false</c> otherwise.</returns>
         [NonAction]
-        public virtual bool TryValidateModel([NotNull] object model, string prefix)
+        public virtual bool TryValidateModel(
+            [NotNull] object model, 
+            string prefix)
         {
             if (BindingContext == null)
             {

src/Microsoft.AspNet.Mvc.ViewFeatures/ValidateAntiforgeryTokenAuthorizationFilter.cs

@@ -16,9 +16,9 @@ namespace Microsoft.AspNet.Mvc
             _antiforgery = antiforgery;
         }
 
-        public async Task OnAuthorizationAsync([NotNull] AuthorizationContext context)
+        public Task OnAuthorizationAsync([NotNull] AuthorizationContext context)
         {
-            await _antiforgery.ValidateRequestAsync(context.HttpContext);
+            return _antiforgery.ValidateRequestAsync(context.HttpContext);
         }
     }
 }

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewComponents/ContentViewComponentResult.cs

@@ -69,9 +69,9 @@ namespace Microsoft.AspNet.Mvc
         /// </summary>
         /// <param name="context">The <see cref="ViewComponentContext"/>.</param>
         /// <returns>A completed <see cref="Task"/>.</returns>
-        public async Task ExecuteAsync([NotNull] ViewComponentContext context)
+        public Task ExecuteAsync([NotNull] ViewComponentContext context)
         {
-            await context.Writer.WriteAsync(EncodedContent.ToString());
+            return context.Writer.WriteAsync(EncodedContent.ToString());
         }
     }
 }

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewComponents/DefaultViewComponentHelper.cs

@@ -88,16 +88,16 @@ namespace Microsoft.AspNet.Mvc.ViewComponents
             }
         }
 
-        public async Task RenderInvokeAsync([NotNull] string name, params object[] arguments)
+        public Task RenderInvokeAsync([NotNull] string name, params object[] arguments)
         {
             var descriptor = SelectComponent(name);
-            await InvokeCoreAsync(_viewContext.Writer, descriptor, arguments);
+            return InvokeCoreAsync(_viewContext.Writer, descriptor, arguments);
         }
 
-        public async Task RenderInvokeAsync([NotNull] Type componentType, params object[] arguments)
+        public Task RenderInvokeAsync([NotNull] Type componentType, params object[] arguments)
         {
             var descriptor = SelectComponent(componentType);
-            await InvokeCoreAsync(_viewContext.Writer, descriptor, arguments);
+            return InvokeCoreAsync(_viewContext.Writer, descriptor, arguments);
         }
 
         private ViewComponentDescriptor SelectComponent(string name)
@@ -126,7 +126,7 @@ namespace Microsoft.AspNet.Mvc.ViewComponents
                 componentType.FullName));
         }
 
-        private async Task InvokeCoreAsync(
+        private Task InvokeCoreAsync(
             [NotNull] TextWriter writer,
             [NotNull] ViewComponentDescriptor descriptor,
             object[] arguments)
@@ -140,7 +140,7 @@ namespace Microsoft.AspNet.Mvc.ViewComponents
                     Resources.FormatViewComponent_IViewComponentFactory_ReturnedNull(descriptor.Type.FullName));
             }
 
-            await invoker.InvokeAsync(context);
+            return invoker.InvokeAsync(context);
         }
 
         private void InvokeCore(

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewComponents/ViewComponentHelperExtensions.cs

@@ -21,16 +21,16 @@ namespace Microsoft.AspNet.Mvc
             helper.RenderInvoke(typeof(TComponent), args);
         }
 
-        public static async Task<HtmlString> InvokeAsync<TComponent>([NotNull] this IViewComponentHelper helper,
+        public static Task<HtmlString> InvokeAsync<TComponent>([NotNull] this IViewComponentHelper helper,
             params object[] args)
         {
-            return await helper.InvokeAsync(typeof(TComponent), args);
+            return helper.InvokeAsync(typeof(TComponent), args);
         }
 
-        public static async Task RenderInvokeAsync<TComponent>([NotNull] this IViewComponentHelper helper,
+        public static Task RenderInvokeAsync<TComponent>([NotNull] this IViewComponentHelper helper,
             params object[] args)
         {
-            await helper.RenderInvokeAsync(typeof(TComponent), args);
+            return helper.RenderInvokeAsync(typeof(TComponent), args);
         }
     }
 }

src/Microsoft.AspNet.Mvc.WebApiCompatShim/ActionResults/BadRequestErrorMessageResult.cs

@@ -28,10 +28,10 @@ namespace System.Web.Http
         public string Message { get; private set; }
 
         /// <inheritdoc />
-        public override async Task ExecuteResultAsync(ActionContext context)
+        public override Task ExecuteResultAsync(ActionContext context)
         {
             context.HttpContext.Response.StatusCode = StatusCodes.Status400BadRequest;
-            await base.ExecuteResultAsync(context);
+            return base.ExecuteResultAsync(context);
         }
     }
 }

src/Microsoft.AspNet.Mvc.WebApiCompatShim/ActionResults/InvalidModelStateResult.cs

@@ -38,10 +38,10 @@ namespace System.Web.Http
         public bool IncludeErrorDetail { get; private set; }
 
         /// <inheritdoc />
-        public override async Task ExecuteResultAsync(ActionContext context)
+        public override Task ExecuteResultAsync(ActionContext context)
         {
             context.HttpContext.Response.StatusCode = StatusCodes.Status400BadRequest;
-            await base.ExecuteResultAsync(context);
+            return base.ExecuteResultAsync(context);
         }
     }
 }