ASP.NET中的HostingEnvironment.QueueBackgroundWorkItem（）用于小型后台任务

Question

I came a across a nice little tool that has been added to ASP.NET in v4.5.2

I am wandering how safe it is and how one can effectively utilize it in an ASP.NET MVC or Web API scenario.

I know I am always wanting to do a quick and simple fire and forget task in my web applications. For example:

• Sending an emails/s
• Sending push notifications
• Logging analytics or errors to the db

Now typically I just create a method called

public async Task SendEmailAsync(string to, string body)
{
 //TODO: send email
}

and I would use it like so:

public async Task<ActionResult> Index()
{
 ...
 await SendEmailAsync(User.Identity.Username, "Hello");
return View(); 
}

now my concern with this is that, I am delaying the user in order to send my email to them. This doesn't make much sense to me.

So I first considered just doing:

Task.Run(()=> SendEmailAsync(User.Identity.Username, "Hello"));

however when reading up about this. It is apparently not the best thing to do in IIS environment. (i'm not 100% sure on the specifics).

So this is where I came across HostingEnvironment.QueueBackgroundWorkItem(x=> SendEmailAsync(User.Identity.Username, "Hello"));

This is a very quick and easy way to offload the send email task to a background worker and serve up the users View() much quicker.

Now I am aware this is not for tasks running longer than 90 seconds and is not 100% guaranteed executution.

But my question is:

Is HostingEnvironment.QueueBackgroundWorkItem() sufficient for: sending emails, push notifications, db queries etc in a standard ASP.NET web site.

Answer 1

It depends.

---

The main benefit of QueueBackgroundWorkItem is the following, emphasis mine ( source ):

Differs from a normal ThreadPool work item in that ASP.NET can keep track of how many work items registered through this API are currently running, and the ASP.NET runtime will try to delay AppDomain shutdown until these work items have finished executing.

Essentially, QueueBackgroundWorkItem helps you run tasks that might take a couple of seconds by attempting not to shutdown your application while there's still a task running.

Running a normal database query or sending out a push notification should be a matter of a couple hundred milliseconds (or a few seconds); neither should take a very long time and should thus be fine to run within QueueBackgroundWorkItem .

However, there's no guarantee for the task to finish — as you said, the task is not await ed. It all depends on the importance of the task to execute. If the task must complete, it's not a good candidate for QueueBackgroundWorkItem .