How do you measure the progress of a web service call?

Question

I have an ASP.NET web service which does some heavy lifting, like say,some file operations, or generating Excel Sheets from a bunch of crystal reports. I don't want to be blocked by calling this web service, so i want to make the web service call asynchronous. Also, I want to call this web service from a web page, and want some mechanism which will allow me to keep polling the server so that i can i can show some indicator of progress on the screen, like say, the number of files that have been processed. Please note that i do not want a notification on completion of the web method call, rather, i want a live progress status. How do i go about it?

Answer 1

Have the initial "start report generation" web service call create a task in some task pool, and return the caller the ID of the task.

Then, provide another method that returns the "percent done" for a given taskId.

Provide a third method that returns the actual result for a completed task.

Answer 2

Easiest way would be to have the Web Service update a field on a database with the progress of the call, and then create a Web Service that queries that field and returns the value.

Answer 3

Write a separate method on the server that you can query by passing the ID of the job that has been scheduled and which returns an approximate value between 0-100 (or 0.0 and 1.0, or whatever) of how far along it is.

E.g. in REST-style, you could make a GET request to http://yourserver.com/app/jobstatus/4133/ which would return a simple '52' as text/plain. Then you just have to query that every (second? two seconds? ten seconds?) to see how far along it is.

How you actually accomplish the monitoring on the backend hugely depends on what your process is and how it works.

Answer 4

Make the web service to return some sort of task ID or session ID. Make another web method to query with that ID, which returns the information needed (% completion, list of files, whatever). Poll this method at some interval from the client.

Use a database to store the process information, if you do this in memory of the web service, this will not scale well in web farm environment, as it may happen that the task runs on another server, than the one you are polling.

EDIT: I just saw another similar answer, and comment to it. The commenter is right - you can use in-memory table to avoid disk operations, but still using a separate db server.

Answer 5

I think XML web service is slow, so creating multiple methods and polling the progress will be extremely slow and will generate huge load on the server. I wouldn't do it in production environment. I see the same (but smaller) problems with database polling.

Try SOAP extensions instead. It implements an event-driven model. See Adding a Progress Bar to Your Web Service Client Application on MSDN.

Answer 6

You can also use SoapExtensions to notify your client of the download/process progress. The server can then send events to the client. Nothing in the client has to be changed if you don't use it.

Allows for something like this in your client:

//...
private localhost.MyWebServiceService _myWebService = new localhost.MyWebServiceService ();
_myWebService.processDelegate += ProgressUpdate;
_myWebService.CallHeavyMethod();
//...

private void ProgressUpdate(object sender, ProgressEventArgs e)
{
  double progress = ((double)e.ProcessedSize / (double)e.TotalSize) * 100.00;
  //Show Progress...
}