CODEWITHSUNDEEP
sqlasp.netstored-proceduresasynchronousasp-classic
MonkeyMagix
MonkeyMagix

Reputation: 707

Ensure a web server's query will complete even if the client browser page is closed

I am trying to write a control panel to

  1. Inform about certain KPIS
  2. Enable the user to init certain requests / jobs by pressing a button that then runs a stored proc on the DB or sets a specific setting etc

So far, so good, except I would like to run some bigger jobs where the length of time that the job is running for is unknown and could run over both the script timeout period AND the time the user is willing to wait for a response.

What I want is a "fire and forget" process so the user hits the button and even if they kill the page or turn off their phone they know the job has been initiated and WILL complete.

I was looking into C# BeginExecuteNonQuery which is an async call to the query so the proc is fired but the control doesn't have to wait for a response from it to carry on. However I don't know what happens when the page/app that fired it is shut.

Also I was thinking of some sort of Ajax command that fires the code in a page behind the scenes so the user doesn't know about it running but then again I believe if the user shuts the page down the script will die and the command will die on the server as well.

The only way for certain I know of is a "queue" table where jobs are inserted into this table then an MS Agent job comes along every minute or two checking for new inserts and then runs the code if there is any. That way it is all on the DB and only a DB crash will destroy it. It won't help with multiple jobs waiting to be run concurrently that both take a long time but it's the only thing I can be sure of that will ensure the code is run at all.

Any ideas?

Any language is okay.

Upvotes: 1

Views: 676

Answers (3)

ErikE
ErikE

Reputation: 50271

Since web browsers are unconnected, requests from them always take the full amount of time. The governing factor isn't what the browser does, but how long the web site itself will allow an action to continue.

IIS (and in general, web servers) have a timeout period for requests, where if the work being done takes simply too long, the request is terminated. This would involve abruptly stopping whatever is taking so long, such as a database call, running code, and so on.

Simply making your long-running actions asynchronous may seem like a good idea, however I would recommend against that. The reason is that in ASP and ASP.Net, asynchronously-called code still consumes a thread in a way that blocks other legitimate request from getting through (in some cases you can end up consuming two threads!). This could have performance implications in non-obvious ways. It's better to just increase the timeout and allow the synchronously blocking task to complete. There's nothing special you have to do to make such a request complete fully, it will occur even if the sender closes his browser or turns off his phone immediately after (presuming the entire request was received).

If you're still concerned about making certain work finish, no matter what is going on with the web request, then it's probably better to create an out-of-process server/service that does the work and to which such tasks can be handed off. Your web site then invokes a method that, inside the service, starts its own async thread to do the work and then immediately returns. Perhaps it also returns a request ID, so that the web page can check on the status of the requested work later through other methods.

Upvotes: 1

johna
johna

Reputation: 10752

From my experience a Classic ASP or ASP.NET page will run until complete, even if the client disconnects, unless you have something in place for checking that the client is still connected and do something if they are not, or a timeout is reached.

However, it would probably be better practice to run these sorts of jobs as scheduled tasks.

On submitting your web page could record in a database that the task needs to be run and then when the scheduled task runs it checks for this and starts the job.

Many web hosts and/or web control panels allow you to create scheduled tasks that call a URL on schedule.

Alternately if you have direct access to the web server you could create a scheduled task on the server to call a URL on schedule.

Or, if ASP.NET, you can put some code in global.asax to run on a schedule. Be aware though, if your website is set to stop after a certain period of inactivity then this will not work unlesss there is frequent continuous activity.

Upvotes: 0

Abhishek Singh
Abhishek Singh

Reputation: 92

You may use asynchronous method and call the query from this method. Your simple method can be changed in to a asynch method in the following manner.

Consider that you have a Test method to be called asynchronously -

     Class AsynchDemo
     {       
            public string TestMethod(out int threadId) 
            {

              //call your query here
            }

           //create a asynch handler delegate: 

           public delegate string AsyncMethodCaller(out int threadId);
     }

In your main program /or where you have to call the Test Method:

     public static void Main() 
     {

        // The asynchronous method puts the thread id here. 
        int threadId;

        // Create an instance of the test class.
        AsyncDemo ad = new AsyncDemo();

        // Create the delegate.
        AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

        // Initiate the asychronous call.
        IAsyncResult result = caller.BeginInvoke( 
            out threadId, null, null);


        // Call EndInvoke to wait for the asynchronous call to complete, 
        // and to retrieve the results. 
        string returnValue = caller.EndInvoke(out threadId, result);

        Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
            threadId, returnValue);

   }

Upvotes: 0

Related Questions