Asynchronous Programming in ASP.NETChris Dufour, ASP .NET MVPSoftware Architect, Compuware

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Agenda• ASP.NET page lifecycle• Load test synchronous application• History of Async support in ASP.NET• TAP (Task-based Asynchronous Pattern)• Asynchronize the application• Load test asynchronous application

ASP.NET Page Lifecycle

demoLoad Test Synchronous Page

Sync vs. Async• Synchronous call

• Caller WAITS for method to complete• “Blocking”• Easy to program/understand

• Asynchronous call• Method returns immediately to caller and executes callback

(continuation) when complete• “Non-blocking”• Run several methods concurrently• Scalability• Harder to program

Asynchronous History

• Call BeginXxx to start doing work• Returns IAsyncResult which reflects status• Doesn’t always run async• Problems with thread affinity

• Call EndXxx to get the actual result value• No built-in support for async pages in

ASP.NET

.NET 1.1 - APM (Asynchronous Programming Model)

Asynchronous History

• Call XxxAsync to start work• Often no way to get status while in-flight• Problems with thread affinity

• Subscribe to XxxCompleted event to get result

• Introduces support for Async pages in ASP.NET

.NET 2.0 - EAP (Event-Based Asynchronous Pattern)

ASP.NET Asynchronous Page Lifecycle

Asynchronous Data Bindingpublic partial class AsyncDataBind : System.Web.UI.Page{ private SqlConnection _connection; private SqlCommand _command; private SqlDataReader _reader;

protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { // Hook PreRenderComplete event for data binding this.PreRenderComplete += new EventHandler(Page_PreRenderComplete);

// Register async methods AddOnPreRenderCompleteAsync(new BeginEventHandler(BeginAsyncOperation), new EndEventHandler(EndAsyncOperation) ); } } IAsyncResult BeginAsyncOperation (object sender, EventArgs e, AsyncCallback cb, object state) { string connect = WebConfigurationManager.ConnectionStrings ["PubsConnectionString"].ConnectionString; _connection = new SqlConnection(connect); _connection.Open(); _command = new SqlCommand( "SELECT title_id, title, price FROM titles", _connection); return _command.BeginExecuteReader (cb, state); }

void EndAsyncOperation(IAsyncResult ar) { _reader = _command.EndExecuteReader(ar); }

protected void Page_PreRenderComplete(object sender, EventArgs e) { Output.DataSource = _reader; Output.DataBind(); }

public override void Dispose() { if (_connection != null) _connection.Close(); base.Dispose(); }}

Asynchronous History

• Call XxxAsync to start work• Returns Task (or Task<T>) to reflect in-flight status• Problems with thread affinity

• No second method or event

.NET 4.0 – TPL (Task Parallel Library)

Task<int> t = SomethingAsync(…);//do work, checking t.Statusint r = t.Result

Asynchronous History

• Works on top of TPL• Introduces 2 new contextual key words• Async marks a method as asynchronous• Await yields control while waiting on a task to complete

• Lets us write sequential code which is not necessarily synchronous

• Takes care of sticky threading & performance issues related to Task<T>

.NET 4.5 – TAP (Task-Based Asynchronous Pattern)

TAPprotected void Page_Load(...){ int r = DoWork();}

private int DoWork(){ DoSomeWork; return 1;}

TAPprotected void Page_Load(...){ int r = DoWork();}

private int DoWork(){ DoSomeWork; return 1;}

Protected async void Page_Load(...){ int r = await DoWorkAsync();}

Private async Task<int> DoWorkAsync(){ await Task.Run(DoSomeWork); return 1;}

demoAsynchronize the Application

Thank You