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 Start I/O Blocked
Process
Asynchronous I/O
Start I/O
Blocked
Process
Background I/O
Background 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: string DoOperation(int param1, double param2); Into: IAsyncResult BeginDoOperation(int param1, double param2, AsyncCallback callback, object state); string EndDoOperation(IAsyncResult asyncResult);
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 method MethodCompleted event CancelAsync method
Uses AsyncOperationManager internally

10. Task Parallel Library
New framework for parallel and async work in .NET 4.0
Convert: string DoOperation(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 method IAsyncResult BeginDoOperation(int param1, double param2, AsyncCallback callback, object state); string EndDoOperation(IAsyncResult asyncResult); 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 (
IHttpAsyncHandler (
F# Async Workflows (
Reactive Extensions for .NET (
Axum (