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I'm aware of the model that involves a scheduled task runninng in the back ground which runs jobs registered with a web request but how about this for an idea that keeps everything within ASP.net...

  1. User uploads a CSV file with, perhaps, several thousand rows. The rows are persisted to the database. I think this would take maybe a minute or so which would be an acceptable wait.

  2. Request returns to the browser and then an automatic Ajax request would go back to the server and request, say, ten rows at a time and process them. (Each row requires a number of web service requests.)

  3. Ajax call returns, display is updated and then another automatic Ajax request goes back for more rows. This repeats until all rows are completed.

  4. If user leaves the web page, then they could return and restart the job.

Any thoughts?

Cheers, Ian.

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    hmm, not a complete answer to the question but have you ever looked at SignalR project. It is a perfect choice for persistent connection implementation for .Net. Commented Nov 20, 2011 at 11:42
  • That looks pretty cool. I suppose I could just run a long running request and get feedback sent back from the server. Why doesn't the web browser time out though? Commented Nov 20, 2011 at 12:05
  • why do you need to keep within a asp.net request? Commented Nov 20, 2011 at 12:19
  • I don't. I just think its simpler not having to worry about a scheduled task running in the background. Commented Nov 20, 2011 at 12:30
  • One complication though with doing it from a web request is, as I mentioned, is if the user closes the browser they'll have to restart the work. Although I suppose one could always make them restart from scratch. Additionally, this app is for a migration so I think a relatively quick and clunky implementation should suffice. Commented Nov 20, 2011 at 12:37

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If i get you right, you actually dont need any "interaction" between background jobs and the long-running request, you just want to "lauch" background jobs with incoming requests? Not such a good idea. Take a look at the Quartz.NET project, it is scheduler embeddable into ASP.NET application, it will handle this stuff for you without need of requests. Of course, if there is app pool shutdown, also your scheduler goes down, but this you cant guarantee not to happen even with your long-running requests solution, dependent on browser waiting on other side.

Also take a look on this interesting article from phil haack on this topic, with his own little scheduler library specific for ASP.NET :

http://haacked.com/archive/2011/10/16/the-dangers-of-implementing-recurring-background-tasks-in-asp-net.aspx

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A server side program (or ideally service) could still be quick and dirty and would be more reliable. You could still do step 1 as you have proposed, upload the file and insert the data ( don't forget to increase the maxRequestLength time out value in the web.config ). Then have a program running on the server that checks for new records and processes them.

If the user needs status you could store an entry in the database for each file and update the database record when the import is complete.

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I think I'd go with Windows Scheduler just so I don't need to re-implement a timer mechanism. Also I could configure it to only run one instance at a time so that I didn't need to worry about database locking. I've had this debate between service and scheduler before on here and I think a scheduled exe is the right choice. Also if I used a server side program then I might as well have that insert the data so that the web request is as quick as possible - it would just create a 'task' row and stick the csv file in it.
Or perhaps I'd just use Quartz.net.
Quartz.net is a great solution for running scheduled background tasks. Works great & you can add all sorts of stuff like durable jobs, clustering, etc.
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Maybe I'm reading the question and interpreting it in a weird way, but why couldn't you read the file into a database and store in a table the current line of the file that you've completed through. You could then track your progress via the db and just send small json objects telling the user how far along you are. That way if their connection drops you can keep processing their request, and if they return later you can notify them of how far along the job is. Also, if multiple clients are connecting you can use the db to queue and throttle (by serializing) the workload. Or if the user connects mid-job with another file, then their new request will be queued up after their current job.

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Yes that's what I'm going to do now. The web request hands the job over to a background process and then just calls back for status reports.

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