c# - ASP.NET 身份发送电子邮件 : TaskCanceledException

Question

我尝试在 asp.net identity 2.0 应用程序中发送验证电子邮件地址电子邮件，但收到 TaskCanceledException 错误。

我尝试了这个线程中的内容:Asp.Net Identity 2.0 - How to Implement IIdentityMessageService to do Async SMTP using SmtpClient?

如果我使用 await 应用程序将永远运行:没有错误消息。但第二个选项返回错误。

错误抛出在:return smtpClient.SendMailAsync(msg);

IdentityConfig.cs

    public async Task SendAsync(IdentityMessage message)
    {
        // Plug in your email service here to send an email.

        try
        {
            #region formatter
            string text = string.Format("Please click on this link to {0}: {1}", message.Subject, message.Body);
            string html = "Please confirm your account by clicking this link: <a href=\"" + message.Body + "\">link</a><br/>";

            html += HttpUtility.HtmlEncode(@"Or click on the copy the following link on the browser:" + message.Body);
            #endregion

            MailMessage msg = new MailMessage();
            msg.From = new MailAddress("");
            msg.To.Add(new MailAddress(message.Destination));
            msg.Subject = message.Subject;
            msg.AlternateViews.Add(AlternateView.CreateAlternateViewFromString(text, null, MediaTypeNames.Text.Plain));
            msg.AlternateViews.Add(AlternateView.CreateAlternateViewFromString(html, null, MediaTypeNames.Text.Html));

            using (var smtpClient = new SmtpClient())
            {
                smtpClient.EnableSsl = true;
                smtpClient.SendCompleted += (s, e) => { smtpClient.Dispose(); };
                await smtpClient.SendMailAsync(msg);
            }


        }
        catch (Exception ex)
        {

            throw ex;
        }


    }

注册.aspx.cs

        protected void CreateUser_Click(object sender, EventArgs e)
    {
        var manager = Context.GetOwinContext().GetUserManager<ApplicationUserManager>();
        var user = new ApplicationUser()
        {
            UserName = Email.Text,
            Email = Email.Text,
            UserProfileInfo = new UserProfileInfo
            {
                FirstName = Firstname.Text,
                LastName = Lastname.Text,
                Adress = Adress.Text,
                Zip = Zip.Text,
                City = City.Text,
                Mobile = Mobile.Text

            }

        };
        IdentityResult result = manager.Create(user, Password.Text);
        if (result.Succeeded)
        {
            // For more information on how to enable account confirmation and password reset please visit http://go.microsoft.com/fwlink/?LinkID=320771
            string code = manager.GenerateEmailConfirmationToken(user.Id);
            string callbackUrl = IdentityHelper.GetUserConfirmationRedirectUrl(code, user.Id, Request);
            manager.SendEmail(user.Id, "Confirm your account", "Please confirm your account by clicking <a href=\"" + callbackUrl + "\">here</a>.");

            manager.AddToRole(user.Id, "Konsument");
            IdentityHelper.SignIn(manager, user, isPersistent: false);
            IdentityHelper.RedirectToReturnUrl(Request.QueryString["ReturnUrl"], Response);
        }
        else
        {
            ErrorMessage.Text = result.Errors.FirstOrDefault();
        }
    }

Answer 1

@ntl 正确识别了问题:SmtpClient在请求完成之前正在处理实例。但是，我更喜欢使用 async和 await作为解决方案:

public async Task SendAsync(IdentityMessage message)
{
  ...
  using (var smtpClient = new SmtpClient())
  {
    smtpClient.EnableSsl = true;
    smtpClient.SendCompleted += (s, e) => { smtpClient.Dispose(); };
    await smtpClient.SendMailAsync(msg);
  }
}

那么，让我们解决原来的问题:

If i use the await the application just runs forever: no error message.

我感觉您的代码可能正在调用 Task.Wait或 Task<T>.Result在调用 SendAsync 之后.这才是真正的问题:调用代码应该更改为使用 await (这使得调用方法 async 并返回 Task/Task<T> ，这使得 its 调用代码必须使用 await 等)。允许 async通过代码库自然地“成长”。这就是为什么 async 之一我的最佳实践 MSDN article on the subject是“一路异步”。

死锁是因为当你await一个任务，然后 await默认情况下将捕获“当前上下文”(在本例中为 ASP.NET SynchronizationContext )，并使用该上下文恢复 async方法。但是，ASP.NET SynchronizationContext每个请求一次只允许一个线程，因此当调用代码阻塞(通过调用 Wait 或 Result )时，它阻塞了该上下文中的线程和 async方法无法恢复。我更详细地描述了这种死锁情况 on my blog .

最好的解决方案是使用 await ，并使用 async一路走来。