ASP.NET Controller: An asynchronous module or handler completed while an asynchronous operation was still pending

Question

I have a very simple ASP.NET MVC 4 controller:

public class HomeController : Controller
{
    private const string MY_URL = \"http://smthing\";
    private r         


        

Answer 1

The method myWebClient.DownloadStringTaskAsync runs on a separate thread and is non-blocking. A possible solution is to do this with the DownloadDataCompleted event handler for myWebClient and a SemaphoreSlim class field.

private SemaphoreSlim signalDownloadComplete = new SemaphoreSlim(0, 1);
private bool isDownloading = false;

....

//Add to DownloadAsync() method
myWebClient.DownloadDataCompleted += (s, e) => {
 isDownloading = false;
 signalDownloadComplete.Release();
}
isDownloading = true;

...

//Add to block main calling method from returning until download is completed 
if (isDownloading)
{
   await signalDownloadComplete.WaitAsync();
}

Answer 2

Email notification Example With Attachment ..

public async Task SendNotification(string SendTo,string[] cc,string subject,string body,string path)
    {             
        SmtpClient client = new SmtpClient();
        MailMessage message = new MailMessage();
        message.To.Add(new MailAddress(SendTo));
        foreach (string ccmail in cc)
            {
                message.CC.Add(new MailAddress(ccmail));
            }
        message.Subject = subject;
        message.Body =body;
        message.Attachments.Add(new Attachment(path));
        //message.Attachments.Add(a);
        try {
             message.Priority = MailPriority.High;
            message.IsBodyHtml = true;
            await Task.Yield();
            client.Send(message);
        }
        catch(Exception ex)
        {
            ex.ToString();
        }
 }