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ASP.NET MVC5: Asynchronous Controllers & Cancellation Token

Asynchronous Controller benefits those situations where a web page has to perform a long running task and user cannot interact with other features of the website. Cancellation Token on the other hand is an important part of the Asynchronous Controller.

Cancellation Token comes in handy when user want to cancel the long running process or to navigate to a new page. In a non-asynchronous controller environment whenever a long or slow processing is done on a web page, the interaction of the user with the web page will be compromised which results into web page being stuck, which apparently seems like webserver is down. Consider a situation where webserver take about 2 to 5 minutes to complete a task and even if user click page refresh, the response from webserver seems non-responsive, this happens because when a user click refresh, there is no way to signal the running process that user has canceled the process, hence, that process will continues to perform and the moment the process completes the action, the page will proceed with the designated user action. In such scenarios, it is important that at each cancellation, running process should be signaled and the correspondent proceeding task like long insertion of database should also be informed about the cancelling signal. The need of cancellation token is beautifully explained by Dave Paquette in his post on Cancelling Long Running Queries in ASP.NET MVC and Web API.

In today's tutorial, I will demonstrate how to write an asynchronous controller with a cancellation token along with configuration of the web application to stay alive until the long running process completes.

Following are some prerequisites before you proceed any further in this tutorial:


1) Knowledge about ASP.NET MVC5.  
2) Knowledge about ADO.NET.  
3) Knowledge about entity framework.
4) Knowledge about HTML.
5) Knowledge about Javascript.
6) Knowledge about AJAX.  
7) Knowledge about CSS.
8) Knowledge about Bootstrap.  
9) Knowledge about C# programming.  
10) Knowledge about C# LINQ.
11) Knowledge about JQuery.

You can download the complete source code for this tutorial or you can follow the step by step discussion below. The sample code is developed in Microsoft Visual Studio 2015 Enterprise. I am using random tables extract from Adventure Works Sample Database. I have also placed ".BAK" file for SQL server, in case anyone is interested to execute the solution.

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1) Create new MVC5 web application project and name it "ImmediateRefreshWithLongDBQuery".
2) Open "_Layout.cshtml" file under "Views->Shared" folder and replace existing code with following:

<!DOCTYPE html>  
   <meta charset="utf-8" />  
   <meta name="viewport" content="width=device-width, initial-scale=1.0">  
   <!-- Font Awesome -->  
   <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css" />  
   <!-- Data table -->  
   <link rel="stylesheet" href="https://cdn.datatables.net/1.10.10/css/dataTables.bootstrap.min.css " />  
   @* Custom *@  
   <div class="navbar navbar-inverse navbar-fixed-top">  
     <div class="container">  
       <div class="navbar-header">  
         <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">  
           <span class="icon-bar"></span>  
           <span class="icon-bar"></span>  
           <span class="icon-bar"></span>  
       <div class="navbar-collapse collapse">  
         <ul class="nav navbar-nav">  
           <li>@Html.ActionLink("Home", "Index", "Home")</li>  
           <li>@Html.ActionLink("Slow Page", "IndexSlow", "Home")</li>  
   <div class="container body-content">  
     <hr />  
         <p><strong>Copyright &copy; @DateTime.Now.Year - <a href="http://asmak9.blogspot.com/">Asma's Blog</a>.</strong> All rights reserved.</p>  
   <!-- Data Table -->  
   <script src="https://cdn.datatables.net/1.10.10/js/jquery.dataTables.min.js" type="text/javascript"></script>  
   <script src="https://cdn.datatables.net/1.10.10/js/dataTables.bootstrap.min.js" type="text/javascript"></script>  
   @RenderSection("scripts", required: false)  

Here, I have simply altered the existing layout and incorporate links to require scripts and styles.  

3) Create new page called "Index.cshtml" under "Views->Home" folder and place following code in it:

   ViewBag.Title = "Immediate Refresh with Slow DB Query";  
 <div class="jumbotron">  
   <h1>Simple Page</h1>  
   <p class="lead">This is a simple normal speed page.</p>  

Here, I am simply creating a page heading.

4) Create new page called "IndexSlow.cshtml" under "Views->Home" folder and place following code in it:

   ViewBag.Title = "Immediate Refresh with Slow DB Query";  
 <div class="row">  
   <div class="panel-heading">  
     <div class="col-md-8 custom-heading3">  
         <i class="fa fa-table"></i>  
         <span>Slow Loading Page</span>  
 <div class="row">  
   <section class="col-md-12 col-md-push-0">  

Here, I am simply creating a page heading and section for my partial view in which I will be displaying my random slow loaded list from webserver.  

5) Now, create new partial page under "Views->Home" folder, name it "_ViewListPartial.cshtml" and place following code in it:

   <div class="well bs-component">  
     <br />  
     <div class="row">  
         <table class="table table-striped table-bordered table-hover"  
               <th>First Name</th>  
               <th>Middle Name</th>  
               <th>Last Name</th>  

Here, I have created a table holder that will be integrated with Datatables plugin with data from server side. I have only provided table header information here, since, the data will be integrated from server side.

6) Now, create new script file under "Scripts" folder, name it "custom-datatable.js" and place following code in it:

$(document).ready(function ()  
     "columnDefs": [  
       { "width": "5%", "targets": [0] },  
       { "className": "text-center custom-middle-align", "targets": [0, 1, 2, 3, 4] },  
         "processing": "<div class='overlay custom-loader-background'><i class='fa fa-cog fa-spin custom-loader-color'></i></div>"  
     "processing": true,  
     "serverSide": true,  
         "url": "/Home/GetData",  
         "type": "POST",  
         "dataType": "JSON"  
     "columns": [  
           { "data": "Sr" },  
           { "data": "Title" },  
           { "data": "FirstName" },  
           { "data": "MiddleName" },  
           { "data": "LastName" }  

In the above code, I have configured the plugin to load data from server side.  

7) I have used entity framework ado.net database first approach to create my model out of my store procedure. After you have created the model from the database, you need to add following line into your "*Model.Context.tt" file. Find your model constructor in that file and add following line i.e.

((IObjectContextAdapter)this).ObjectContext.CommandTimeout = 60000; // 60 mins. 

What above line will do is that it will allow webserver to process long running database queries without timing out the webserver. I have used 60 minutes wait before timeout. We are adding the code in *.tt file because whenever the model is refreshed, our added line will be automatically added into constructor.

8) Now, In "HomeController.cs" file add following function to load data database:

 #region Load Data  
     /// <summary>  
     /// Load data method.  
     /// </summary>  
     /// <param name="cancellationToken">Cancellation token parameter</param>  
     /// <returns>Returns - Data</returns>  
     private async Task<List<sp_slow_test_Result>> LoadData(CancellationTokenSource cancellationToken)  
       // Initialization.  
       List<sp_slow_test_Result> lst = new List<sp_slow_test_Result>();  
         // Initialization.  
         testEntities databaseManager = new testEntities();  
         // Loading.  
         lst = await databaseManager.Database.SqlQuery<sp_slow_test_Result>("EXEC sp_slow_test").ToListAsync(cancellationToken.Token);  
       catch (Exception ex)  
         // info.  
       // info.  
       return lst;  

In the above code we are loading data from database using store procedure with the signal of cancellation token pass to our resulting list conversion method.

9) Now, let's add our Asynchronous Controller into "HomeController.cs" file i.e.

 #region Get data method.  
     /// <summary>  
     /// GET: /Home/GetData  
     /// </summary>  
     /// <param name="cancellationToken">Cancellation token parameter</param>  
     /// <returns>Return data</returns>  
     public async Task<ActionResult> GetData(CancellationToken cancellationToken)  
       // Initialization.  
       JsonResult result = new JsonResult();  
         // Initialization.  
         CancellationToken disconnectedToken = Response.ClientDisconnectedToken;  
         var source = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, disconnectedToken);  
         // Initialization.  
         string search = Request.Form.GetValues("search[value]")[0];  
         string draw = Request.Form.GetValues("draw")[0];  
         string order = Request.Form.GetValues("order[0][column]")[0];  
         string orderDir = Request.Form.GetValues("order[0][dir]")[0];  
         int startRec = Convert.ToInt32(Request.Form.GetValues("start")[0]);  
         int pageSize = Convert.ToInt32(Request.Form.GetValues("length")[0]);  
         // Loading.  
         List<sp_slow_test_Result> data = await this.LoadData(source);  
         // Total record count.  
         int totalRecords = data.Count;  
         // Verification.  
         if (!string.IsNullOrEmpty(search) &&  
           // Apply search  
           data = data.Where(p => p.Sr.ToString().ToLower().Contains(search.ToLower()) ||  
                       p.Title.ToLower().Contains(search.ToLower()) ||  
                       p.FirstName.ToString().ToLower().Contains(search.ToLower()) ||  
                       p.MiddleName.ToLower().Contains(search.ToLower()) ||  
         // Sorting.  
         data = this.SortByColumnWithOrder(order, orderDir, data);  
         // Filter record count.  
         int recFilter = data.Count;  
         // Apply pagination.  
         data = data.Skip(startRec).Take(pageSize).ToList();  
         // Loading drop down lists.  
         result = this.Json(new { draw = Convert.ToInt32(draw), recordsTotal = totalRecords, recordsFiltered = recFilter, data = data }, JsonRequestBehavior.AllowGet);  
       catch (Exception ex)  
         // Info  
       // Return info.  
       return result;  

In the above code we have created Asynchronous Controller and cancellation token has been passed to it as well. Notice here that when we call this method using Ajax call, we do not need to pass any parameter from Ajax method. The browser will automatically handle the passing of the cancellation token, we only need to capture that cancellation token in our controller method. In the above code, we are also using "[NoAsyncTimeout]" attribute at method level because we do not want our web server to timeout our Asynchronous Controller.

10) Open "Web.config" file and do add following line i.e.

    <httpRuntime targetFramework="4.5" executionTimeout="100000" maxRequestLength="214748364" />  

We are adding the above line because we do not want our webserver to timeout before our long running process gets complete.

11) Now, execute the project and you will be able to see the below web page i.e.

That's about it.

Enjoy!! Coding.

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