Advices on time-consuming procedure in C#

Question

I've developed a program using Delphi that, among some features, does a lot of database reading of float values and many calculations on these values. At the end of these calculations, it shows a screen with some results. These calculations take some time to finish: today, something like 5 to 10 minutes before finally showing up the results screen.

Now, my customers are requesting a .Net version of this program, as almost all of my other programs have already gone to .Net. But I'm afraid that this time-consuming calculation procedure wouldn't fit the web scenario and the program would take the user to some kind of timeout error.

So, I'd like some tips or advices on how to do this kind of procedure. Initially I thought about calling a local executable (that could be even my initial Delphi program, in a console way) and after some time show the result screen in a web page. But, again, I'm afraid this wouldn't be the best approach.

Answer 1

An external process is a reasonable way to go about it. You can fire off a thread inside the ASP.NET process (i.e. just with new Thread()) which could also work, but there are issues around process recycling and pooling that might make this a little harder. simply firing off an external process and then maybe using some Ajax polling to check on it's status on the browser seems like a good solution to me.

Answer 2

FWIW, another pattern that some existing online services use (for instance, ones that do file conversion that may take a few minutes) is having the person put in an email address and just send the results via email once it's done - that way if they accidentally kill their browser or it takes a little longer than expected or whatever, it's no big deal.

Another approach I've taken in the past is basically what Dean suggested - kick it off and have a status page that auto-refreshes, and once it's complete, the status includes a link to results.

Answer 3

How about:

• Create a Web Service that does the fetching/calculation.
• Set the timeout so it wont expire.

YourService.HeavyDutyCalculator svc = new YourService.HeavyDutyCalculator(); svc.Timeout = 10 * 1 * 1000; //Constitutes 10 mins, 10 mins x 1 second x 1000 ms Service.CalculateResult result = svc.Calculate();

Note that you can put -1 if you want it to run infinitely.

MSDN:

Setting the Timeout property to Timeout.Infinite indicates that the request does not time out. Even though an XML Web service client can set the Timeout property to not time out, the Web server can still cause the request to time out on the server side.

• Call that web method inside you web page
• Place a waiting/inProgress image
• Register for web method OnComplete event; and show results upon complete.

You can also update the timeout in your web.config:

<httpRuntime useFullyQualifiedRedirectUrl="true|false"
             maxRequestLength="size in kbytes"
             executionTimeout="seconds"
             minFreeThreads="number of threads"
             minFreeLocalRequestFreeThreads="number of threads"
             appRequestQueueLimit="number of requests"
             versionHeader="version string"/>

Answer 4

Regardless of what else you do you need a progress bar or other status indication to the user. Users are used to web pages that load in seconds, they simply won't realise (even if you tell them in advance) that they have to wait a full 10 minutes for their results.