Implementing a Progress bar for long running task implemented with an ASP.NET MVC 2 AsyncController

Very interesting question! Actually it seems that it is not a task for AsyncController. Async controllers are designed for long-running single-HTTP-query operations at server-side. When you are using async action, this could only help you to release ASP.Net worker thread during some long-running operation(s) and allow it to serve other requests while operation is performed. But from client-side point of view it doesn't matter, is this async controller or not. For client this is just single HTTP request.

You need to redesign this using some long-running queries service in your application. Here is example of controller, that could serve such workflow:

public class LongOperationsController : Controller{    public ActionResult StartOperation(OperationData data)    {         Guid operationId = Guid.NewGuid(); // unique identifier for your operation        OperationsService.DoStartOperation(operationId, data); // service starts to perform operation using separate thread        return new JsonResult(operationId); // operation id should be sent to client to allow progress monitoring    }    public ActionResult GetOperationStatus(Guid operationId)     {        var status = OperationsService.GetStatus(operationId); // this method returns some object, that describes status of operation (e.g. progress, current task etc.)        return new JsonResult(status); // returning it to client    }    public ActionResult GetOperationResult(Guid operationId)    {        var result = OperationsService.GetOperationResult(operationId); // this should throw exception if operation is not yet completed        return new JsonResult(result);    }    public ActionResult ClearOperation(Guid operationId)    {        OperationsService.ClearOperationResult(operationId); // we should delete operation result if it was handled by client        return true;    }}

And here are client-side code, that could interact with this controller:

var operationId;function startOperation(data) {    $.post('/LongOperations/StartOperation', data, function(response) {        operationId = response; // store operationId        startOperationMonitoring(); // start    }, 'json');}function startOperationMonitoring() {    // todo : periodically call updateOperationStatus() to check status at server-side}function updateOperationStatus() {    // todo : get result of GetOperationStatus action from controller     // todo : if status is 'running', update progress bar with value from server, if 'completed' - stop operation monitoring and call finishOperation()}function finishOperation() {    // todo : get result of GetOperationResult action from controller and update UI    // todo : call ClearOperation action from controller to free resources}

This is very basic concept, there are some missed items here, but I hope you will get the main idea. Also it's up to you how to design components of this system, for example:

• use singleton for OperationsService,or not;
• where and how long operation result should be stored (DB? Cache?Session?);
• is it really required to manually release resources and what to do whenclient stopped to monitor operation(user closed browser) etc.

Best luck!