DEVintersectionSession AS12

Building Asynchronous ASP.NET ApplicationsShayne Boyer

spboyer@live.com@spboyer / tattoocoder.com

2© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Agenda

Quick History When is Async Useful Parallelism Tips & Resources

3© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Async in .NET.NET Framework 1.0 / 1.1

1.0 – no async available 1.1 – APM: Async Programming Model

IAsyncResult result = StartProcess(..);

// continue doing other work// checking result.IsCompleted

int final = EndProcess(result);

4© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Async in .NET.NET Framework 2.0

EAP: Event-base Async Pattern

ProcessCompleted += (sender, e) =>{ // process the result here};AsyncProcessStart(…);

5© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Async in .NET.NET Framework 4.0

TPL: Task Parallel Library Returns Task<TResult> Makes composition easy with .ContinueWith, .WhenAll. etc

Task<int> t = ProcessAsync(…);

// process other work// check t.Status, t.IsFaulted, etc.

int result = t.Result;

6© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Async in .NET.NET Framework 4.5

async/await keywords

public async Task<int> Process() {

int result = await CompleteWork();

return result;}

7© DEVintersection. All rights reserved.

http://www.DEVintersection.com

When to AsyncWhen is it most useful?

I/O Database File Network

Parallelism Long Running Tasks

8© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Application Architecture

50 States

Web APIWeb FormsApplication

Warnings db

Demo

WebFormsUsing Async in WebForm Applications

10© DEVintersection. All rights reserved.

http://www.DEVintersection.com

WebFormsNotes

DO NOT async your Page_Load RegisterAsyncTask Set Async=“true” on your .aspx page to enable async pipeline

Demo

MVC / Web APIUsing Async in MVC

12© DEVintersection. All rights reserved.

http://www.DEVintersection.com

MVC / Web APINotes

Simple & Transparent Mark method as async, return Task<T> Use Entity Framework >= 6.1 for async methods

SaveChangesAsync FirstAsync() etc

13© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Parallelism

Task.WhenAll Runs two or more async operations without using any

additional threads Task.Run, ThreadPool.QueueUserWorkItem

Multiple synchronous operations Each will use a new thread from ASP.NET thread pool

Demo

Parallelism

15© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Final Comments

Avoid using Background Threads All threads come from the same pool, using background

threads takes threads from processing new requests. Do not use Task.Wait()

Can easily deadlock ASP.NET process Use Task.WhenAll instead

Avoid Using Task.ContinueWith Puts you on a new thread Cannot get back to initial context, UI thread etc.

Parallel != Async Can use them together or separate. With great power comes great responsibility

16© DEVintersection. All rights reserved.

http://www.DEVintersection.com

Resource & Links

Hanselminutes Podcast – Everything .NET programmers know about Asynchronous Programming is wrong.http://hanselminutes.com/327/everything-net-programmers-know-about-asynchronous-programming-is-wrong

Using Asynchronous Methods in ASP.NET 4.5http://www.asp.net/web-forms/tutorials/aspnet-45/using-asynchronous-methods-in-aspnet-45

Contact Information Twitter: @spboyer Blog: http://www.tattoocoder.com

Questions?

Thank you!

Don’t forget to enter your evaluation of this session using EventBoard!