Response.Redirect issue with Asp.net async

11
votes

I'm new to asp.net 4.5 async and am running into the following with calling response.redirect within an async method. The issue is that the response just "hangs" Has anyone else experienced similar issues with attempting an redirect with async? This code will work in a brand new project, but, does not work with a new page in our existing code. I made sure to gut out everything I could out of our web.config and removed our master page. Hitting a brick wall...any ideas? Thanks!

    protected void Page_Load(object sender, EventArgs e)
    {
        RegisterAsyncTask(new PageAsyncTask(PageLoadAsync));
    }

    private async Task PageLoadAsync()
    {
        var data = await GetData();

        if (data == HttpStatusCode.OK)
            Response.Redirect("http://www.google.com");
    }

    private async Task<HttpStatusCode> GetData()
    {
        using (var client = new HttpClient())
        {
            var response = await client.GetAsync("https://www.google.com");
            return response.StatusCode;
        }
    }
2
c#asp.netasync-awaitresponse.redirect
I dont think you can execute Redirect on async thread – Murali Murugesan
I don't see why you need async, you still need to wait for the HttpClient to respond before finishing loading/rendering the page. And you aren't doing multiple things at the same time. btw: if you have internet connection, google will always work ;) – the_lotus
He needs async because he is doing an I/O intensive task (sending an HTTP request to a remote resource). Imagine that this resource takes long time to respond. You will be jeopardizing your ASP.NET worker thread during this time. Now imagine that this endpoint is hit by 200 users at the same time => your site will die because there won't be any worker threads available to service the requests. That's why it is extremely important to use async in this case. – Darin Dimitrov
@DarinDimitrov, how the worker thread will get the response? or server will push the update(chunks) to client like HTML5 websockets? I still in confusion how RegisterAsyncTask works? – Murali Murugesan
The client.GetAsync method uses an I/O Completion Port. You can read more about them here: msdn.microsoft.com/en-us/magazine/cc163463.aspx. There are no chunks or HTML5 WebSockets in server to server communication. – Darin Dimitrov

2 Answers

21
votes

This code will work in a brand new project, but, does not work with a new page in our existing code.

I assume your existing site has already been upgraded to .NET 4.5.

The first thing to check is that httpRuntime.targetFramework is set to 4.5. This is not set by default when you upgrade.

Edit from comments:

Another thing to check (just in case) is that Page.Async is set to true.

In this case, the solution was to call Response.Redirect("http://www.google.com", false), which explicitly passes false for the endResponse parameter. The default value of true is only for backwards-compatibility reasons as described here.

0
votes

The hack I used is:

  1. I used a static dictionary as var d= new Dictionary<string, bool>(); in the class where my API calling method is written.

  2. I put the code line client.timeout = new System.TimeSpan(0,0,60); for API sending the request.

  3. When API is timed out, it throws the TaskTimeoutException, in the TaskTimeoutExceptioncatch block write code as d.Add("timeout", true);

  4. Now, I created the custom action filter and applied the following code:

    public class MyCustomActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        if(MyApiClass.d.ContainsKey("timeout") && d["timeout"])
        {
            throw new Exception();
        }
    }
}

  5. I applied the [MyCustomActionFilter ] on the action.

  6. When action is executed and enter the custom filter it throws Exception by checking the dictionary entry.

  7. If timeout would have occurred then dictionary entry will be true, so, on the basis of that, we check the entry and throws the exception. Now, we have Application_Error() in Global.asax.cs that catches the exception.

  8. In the Application_Error() we have written the code for redirect to the required page.

NOTE: In step 4 you can create your custom exception to provide more precise detail for logging.