Using Task ContinueWith to delay execution of code

Question

I need to add delay to some code block. I am using Task ContinueWith to achieve that, it works as expected when tested on my machine but the deployed code is not working.

public void DailyReminder()
{        
    //Do somethings
    System.Threading.Tasks.Task.Delay(300000).ContinueWith(t => EmailAlert());  //This should not block UI   
    //Do more things, this should not wait for 300000 ms to get excecuted
}

public void EmailAlert()
{
    //Send Email
}

For Example i need the below code to produce A B C and D only after the 5 sec delay -

using System;
using System.Threading.Tasks;

namespace HelloWorld
{
  class Program
  {
    static void Main(string[] args)
    {      
    Console.WriteLine("A");
      EmailAlert();
       Console.WriteLine("C");
    }
    
    private static async Task EmailAlert()
    {
    Console.WriteLine("B");    
        await Task.Delay(5000);
        Console.WriteLine("D");    
        }
  }
}

Related: [Fire and forget async method in ASP.NET MVC](https://stackoverflow.com/questions/18502745/fire-and-forget-async-method-in-asp-net-mvc), and also [Proper way to start and fire-and-forget asynchronous calls?](https://stackoverflow.com/questions/61316504/proper-way-to-start-and-async-fire-and-forget-call) — Theodor Zoulias, Feb 03 '23 at 07:25
"Do more things" is not waiting for the Delay in this case. It's not awaited... — Jeroen van Langen, Feb 03 '23 at 08:09
You're not providing what your output is compared to what you're expecting. But I'm guessing the problem is because you're not awaiting the EmailAlert() method. Therefore, the "C" often output will before "D". — einord, Feb 15 '23 at 05:54

score 1 · Answer 1 · answered Feb 03 '23 at 07:09

1

You should separate your EmailAlert (which is a fire-and-forget task) and the logic that is not dependent on the task.

public void DailyReminder()
{
  // A discard pattern to make it explicit this is a fire-and-forget
  _ = EmailAlert();
  
  // Additional code that does not depend on the preceding task
}

public async Task EmailAlert()
{
  await Task.Delay(300_000);
  // await Some email sending logic
}

answered Feb 03 '23 at 07:09

rexcfnghk

14,435
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I tired but still it does not work, you can see the sample code on my original question which i have just added. – Himanshu Feb 03 '23 at 09:38
@HimanshuBaunthiyal what isn't working? – rexcfnghk Feb 06 '23 at 02:09

score 1 · Answer 2 · answered Feb 03 '23 at 13:19

1

it works as expected when tested on my machine but the deployed code is not working.

If you're using some kind of shared or cloud hosting, it's normal to have your app shut down when it's done servicing requests for some time. This is why fire-and-forget on ASP.NET is dangerous.

Since you definitely want your email to be sent, fire-and-forget is not an appropriate solution. Instead, you want a basic distributed architecture:

Instead of sending the email from ASP.NET, serialize it to a message sent to a durable queue.
Have a separate background process read that queue and send the actual email.

answered Feb 03 '23 at 13:19

Stephen Cleary

437,863
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My app is set to always running. Can you please go through the attached example code on my original question. – Himanshu Feb 05 '23 at 10:38
`My app is set to always running.` - That decreases the possibility of a shutdown but does not prevent it. – Stephen Cleary Feb 06 '23 at 14:27

score 0 · Answer 3 · answered Feb 03 '23 at 06:30

I'm not sure of where in your code you are trying to create this delay, but you normally don't have the control over how long a thread will be alive when deploying your application to a server.

Normally a thread is created when a user sends a request to the application, and when it returns its response the thread will be stopped.

Also, the web server may close down the entire application when there's no traffic for a while.

The solution for these long running methods is to use Worker services.

You can read more from the documentation at https://learn.microsoft.com/en-us/dotnet/core/extensions/workers

Can you go through my original question once again. i have attached a example. — Himanshu, Feb 03 '23 at 11:32

score -2 · Answer 4 · answered Feb 03 '23 at 06:30

You try use case this :

 public void DailyReminder()
{        
    //Do somethings
    System.Threading.Tasks.Task.Delay(300000).ContinueWith(t => EmailAlert()).Wait();  //This should not block UI   
    //Do more things, this should not wait for 300000 ms to get excecuted
}

public void EmailAlert()
{
    //Send Email
}

Using Task ContinueWith to delay execution of code

4 Answers4