Asynchronous I/O in .NET

1. Asynchronous I/O in .NET

2. What is Async I/O? • Executing I/O in the background, allowing foreground work to proceed • I/O executes and completes in parallel with, and independent of, the application that initiated it • Called “Overlapped I/O” in Win32

3. What is Async I/O? Synchronous I/O Asynchronous I/O

4. Why use Async I/O? • Scalability • Throughput • Threads are expensive • Non-blocking UI • Silverlight

5. Why not Async I/O? • Complexity • Debuggability • Unnecessary?

6. Asynchronous Programming Model • Standard pattern for async work in .NET 3.5 • Convert:stringDoOperation(int param1, double param2);Into:IAsyncResultBeginDoOperation(int param1, double param2,AsyncCallbackcallback, object state);stringEndDoOperation(IAsyncResultasyncResult); • In WCF, use[OperationContract(AsyncPattern = true)]

7. Asynchronous Programming Model • Four ways to complete asynchronous call: • Supply an AsyncCallback • Poll IAsyncResult.IsCompleted • Wait on IAsyncResult.AsyncWaitHandle(blocking) • Call EndXxx method (blocking) • Always call EndXxx method!

8. Asynchronous I/O with APM in .NET 3.5 Demo

9. Event-Based Pattern • Introduced in .NET 2.0 to simplify APM • E.g., PictureBox, SoundPlayer, WebClient • MethodAsync methodMethodCompleted eventCancelAsync method • Uses AsyncOperationManager internally

10. Task Parallel Library • New framework for parallel andasync work in .NET 4.0 • Convert:stringDoOperation(int param1, double param2);Into:Task<string> DoOperation(int param1, double param2);

11. Task Parallel Library • Two ways to complete asynchronous call: • ContinueWith • Call Task<T>.Result or Task.Wait (blocking)

12. Task Parallel Library • Wrap existing APM methodIAsyncResultBeginDoOperation(int param1, double param2,AsyncCallbackcallback, object state);stringEndDoOperation(IAsyncResultasyncResult);with FromAsync:Task<string>.Factory.FromAsync(BeginDoOperation, EndDoOperation,int param1, double param2, object state);

13. Asynchronous I/O with TPL in .NET 4.0 Demo

14. Where to? • ASP.NET Asynchronous Pages (http://msdn.microsoft.com/en-us/magazine/cc163725.aspx) • IHttpAsyncHandler(http://msdn.microsoft.com/en-us/magazine/cc163463.aspx) • F# Async Workflows (http://blogs.msdn.com/dsyme/archive/2007/10/11/introducing-f-asynchronous-workflows.aspx) • Reactive Extensions for .NET(http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx) • Axum(http://msdn.microsoft.com/en-us/devlabs/dd795202.aspx) • http://github.com/bgrainger/AsyncIoDemo