Difference between Task.Run and QueueBackgroundWor

问题:

What exactly is the difference using

Task.Run(() => { 
     LongRunningMethod();
});

or

HostingEnvironment.QueueBackgroundWorkItem(clt => LongRunningMethod());

I tested on an Asp.Net MVC application in which I kept on writing a line to a text file for about 10 minutes inside an asynchronous task which is invoked using Task.Run or QBWI.

It goes fine both using Task and QBWI. My async method keeps on writing to that file without any issues till 10 minutes. No disturbance from IIS I observed regarding its recycling.

So what is special about QueueBackgroundWorkItem then?

回答1:

The documentation has an excellent explanation:

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. This API cannot be called outside of an ASP.NET-managed AppDomain. The provided CancellationToken will be signaled when the application is shutting down.

Task.Factory.StartNew does not register work with the ASP.NET runtime at all. You're running your code for 10 minutes, that makes no difference. IIS recycle happens at particular times which are preset in IIS. If you really want to test whats going on, you can attempt to force a recycle.

回答2:

Below article explains something similar to what you are doing and if you go to the final section "Few more thoughts..." you see the difference highlighted between the two

http://codingcanvas.com/using-hostingenvironment-queuebackgroundworkitem-to-run-background-tasks-in-asp-net/

Basically it says that using queuebackgroundworkitem tasks are registered with ASP.Net runtime and if a process is closed or crashes ASP.NET runtime still gives some grace period for processes to complete.It also involves sending notification to the process so that it can wrap up and perform any finalization tasks whereas all this is not available when you use Task.Run

回答3:

The AppDomain shutdown can only be delayed 90 seconds (It’s actually the minimum of HttpRuntimeSection.ShutdownTimeout and processModel shutdownTimeLimit). If you have so many items queued that they can’t be completed in 90 seconds, the ASP.NET runtime will unload the AppDomain without waiting for the work items to finish.

https://blogs.msdn.microsoft.com/webdev/2014/06/04/queuebackgroundworkitem-to-reliably-schedule-and-run-background-processes-in-asp-net/