Task FromResult vs TaskCompletionSource SetResult

Question

What is the difference concerning the functionality and meaning of the

TaskCompletionSource + SetResult vs Task + FromResult

in the SendAsync method?

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {     if (request.RequestUri.Scheme != Uri.UriSchemeHttps)     {         var response = new HttpResponseMessage(HttpStatusCode.Forbidden) {ReasonPhrase = "HTTPS Required"};         var taskCompletionSource = new TaskCompletionSource<HttpResponseMessage>();         taskCompletionSource.SetResult(response);         return taskCompletionSource.Task;     }     return base.SendAsync(request, cancellationToken); }  protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {     if (!request.RequestUri.Scheme.Equals(Uri.UriSchemeHttps, StringComparison.OrdinalIgnoreCase))     {         HttpResponseMessage reply = request.CreateErrorResponse(HttpStatusCode.BadRequest, "HTTPS is required for security reason.");         return Task.FromResult(reply);     }      return base.SendAsync(request, cancellationToken); } 

Answer 1

Task.FromResult was a new addition in .NET 4.5. It is a helper method that creates a TaskCompletionSource and calls SetResult. If you are using .NET 4 or earlier you will have to use SetResult.

Answer 2

If all you want is to return a completed Task<TResult> with a result (or a completed Task without one), simply use Task.FromResult.

Task.FromResult is a simple tool to create a finished task with a result. TaskCompletionSource is a much more robust tool that supports everything. You can set exceptions, return a non-completed task and set it's result later and so forth

P.S: It seems like you're trying to "fake" async methods by returning a finished task. Although that's the best way to do it, make sure "faking" async is really what you want to accomplish.