Web page perform long task without timing out

Question

Our site has an admin page that allows administrators to kick off a process that copies a given template CMS page out to a couple hundred directories. I guess this process takes a few minutes to run so the page times out. So what I think we need it to do is have the submit button start the task, then have the page poll for results every X seconds until it completes.

I've been trying to figure out how to do this and have seen Phil Haack's popular "Dangers of Implementing Recurring Background Tasks in ASP.NET" post. While a decent argument could be made that an external application should perform this work and not the web server, in reality, it won't be used very often, a web interface will be desired by admins, and we already have a working version of the code, the browser just doesn't wait around long enough to report completion.

I came across HostingEnvironment.QueueBackgroundWorkItem and thought that might work, except it looks like the current HttpContext isn't available to it. I think this might interfere with the CMS API, but I was also planning to use the Session State for my flag to indicate when the task had completed.

I've seen pages, like travel websites, or the SSRS web interface, show a polling page while it does some long-running processing. I don't need anything fancy or intricate for this purpose, I just need to avoid the timeout. Am I on the wrong track with QueueBackgroundWorkItem? If not, how can I tell when the task has finished?

score 1 · Answer 1 · answered Jan 04 '16 at 23:50

You'll probably want to use one of the following...

Application State - to store the state for the processing, this is only an option if your application is on a single server, not multiple systems. You'll want to launch your processing in another thread, that updates the application state when done, so it doesn't block the start request.
SignalR - you can use a message to start the process, and return a message when complete. (again use a separate thread/threadpool)

Other options include Message Queue systems that allow tracking if a ticket is complete, or doing it yourself with a database.

I definitely want to keep it farm-compatible. The task is specific to the user/session. I suppose the session ID could be stored in the Application State to solve that. We're using a session state server so providing the current HttpSessionState to my background thread seems to work. — xr280xr, Jan 07 '16 at 17:35

score 1 · Accepted Answer · answered Jan 05 '16 at 01:20

1

You can use a tool like HangFire in order to start and execute a background task in your server and track it. It could be used in combination with SignalR (as @Tracker1 suggested) for notifications to the client side when the tasks are completed.

answered Jan 05 '16 at 01:20

Hernan Guzman

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This looks like a well rounded solution. In this case, I think a 3rd party API is overkill. – xr280xr Jan 07 '16 at 17:34

xr280xr · Answer 3 · 2016-01-07T17:38:21.517

I resolved the CMS API dependencies on the HttpRequest issues so I didn't have to worry about that anymore. I ended up using HostingEnvironment.QueueBackgroundWorkItem and passed it the current HttpSessionState. When the background thread Action starts, it places an object in session to indicate whether the task is still running, has an error, or has completed successfully. Meanwhile, the page uses jQuery AJAX requests poll an ASP.NET Page Method that reads that status object from session. For the simple purposes of this admin page, it works well. Since we're using a session state server, this should work in a farm too.

Web page perform long task without timing out

3 Answers3