Tackle the Complexity of Async Calls in WPF and Silverlight

1. DEV340 Tackle the Complexity of Async Callsin WPF and Silverlight Brian Noyes Chief Architect IDesign Inc (www.idesign.net)

2. About Brian • Publishing • Developers Guide to Microsoft Prism 4, O’Reilly & Assoc., March 2011 • Developing Applications with Windows Workflow Foundation, LiveLessons training DVD, June 2007 • Smart Client Deployment with ClickOnce, Addison Wesley, January 2007 • Data Binding in Windows Forms 2.0, Addison Wesley, January 2006 • MSDN Magazine, MSDN Online, CoDe Magazine, The Server Side .NET, asp.netPRO, Visual Studio Magazine • Speaking • Microsoft TechEd US, Europe, Malaysia, Visual Studio Connections, DevTeach, INETA Speakers Bureau, MSDN Webcasts Chief ArchitectIDesign Inc. (www.idesign.net) Microsoft Regional Director(www.theregion.com) Microsoft MVP Silverlight E-mail: brian.noyes@idesign.net Twitter: @briannoyes Blog: http://briannoyes.net

3. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

4. Commandments of UI Multithreading • Thou shalt not block the UI thread • Thou shalt not access UI objects on a non-UI thread • Thou shalt not access variables on multiple threads without protection (locks)

5. Multithreading – The Risk • Concurrent access to memory • Member / static variables • Two or more threads • One or more reads • One or more writes • Can corrupt memory depending on when threads are scheduled • Need synchronization locks • Deep end of the programming pool

6. UI Multithreading • Silverlight and WPF use a single thread for UI concerns • WPF – startup thread of the app • Silverlight - Browser thread • Can have many other threads executing in the UI application • Async method calls • Worker threads • Service callbacks

7. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

8. Using Dispatcher • Used to get execution on the UI thread when you are on another thread • (WPF Only) Synchronous from calling thread • Blocking until unit of work complete on UI thread • Async from calling thread • Non-blocking • Work is dispatched asynchronously to the UI thread when current thread time slice is complete • Checking to see if dispatch is needed:

9. SynchronizationContexts • Dispatcher uses DispatcherSynchronizationContext under the covers • Derived from SynchronizationContext • Standard thread dispatch pattern in .NET for objects with thread affinity • Windows Forms, ASP.NET, WPF, Workflow also have implementations • Multithreaded mechanisms can use this to auto-dispatch to the UI thread • Async/Completed pattern • Task class from TPL • Reactive Extensions • Task-based Async Pattern (Async CTP) • WCF message dispatching

10. Working with the Dispatcher Brian Noyes Chief Architect IDesign Inc. (www.idesign.net) demo

11. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

12. Begin/End and Async/Completed Patterns Brian Noyes Chief Architect IDesign Inc. (www.idesign.net) demo

13. Begin/End Async Pattern • Introduced in .NET 1.0 / all platform variants • Most powerful pattern • Polling or callbacks for completion • Can pass state when invoking • Can access waithandles for each invocation for blocking ops • Most complex pattern • More complex method signatures • Have to hold on to IAsyncResult or use callbacks • Have to hold on to object that async work was invoked on • Callbacks happen on background thread

14. Async/Completed Pattern • Introduced in .NET 2.0 • Implemented by some APIs, BackgroundWorker, WCF Proxies • MyOperationAsync method • Invokes target method (MyOperation) on background thread • Same parameter list as target method • void return type • MyOperationCompleted event • Fired by runtime when background thread operation completes • Automatically marshaled the event handler call to the UI thread (if needed) • Event arguments contain strongly typed results • Event arguments contain exception if one was raised

15. BackgroundWorker • Introduced in .NET 2.0 • Available in WPF, Silverlight, Silverlight for Windows Phone • Implements Async/Completed pattern • Point DoWork event at method to execute on background thread • Supports cancellation

16. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

17. Task Parallel Library • Shipped in .NET 4 • Only available in full .NET Framework at this time • Planned to be supported in future version of Silverlight • Use Task class to point to asynchronous work • Dispatches to thread pool thread • Enhances thread management in pool • Continuations • Can schedule on the user interface thread • Exception callbacks • Cancellation supported

18. Parallel Framework (PFX) / PLINQ • Allows simple data parallelization • Parallel.For and Parallel.ForEach methods • PLINQ .AsParallel extension • Executes subsequent LINQ operations concurrently • Smart scheduling of the “appropriate” number of threads • Based on cores, target method complexity, collection size, etc • Items in collection need to be independent

19. TPL and PLINQ Brian Noyes Chief Architect IDesign Inc. (www.idesign.net) demo

20. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

21. Task-based Async Pattern (Async CTP) • New keywords being added to C# and VB • Will be released with the next version • Allows you to write code that looks synchronous, but executes asynchronous • Compile time code generation into async patterns • Public CTP available

22. Task-based Async Pattern (Async CTP) • Uses Task class from Task Parallel Library • New keywords • await • async • Naming and return type conventions • Task<T>, XXXAsync

23. Task-based Async Pattern (Async CTP) Brian Noyes Chief Architect IDesign Inc. (www.idesign.net) demo

24. Agenda • Multithreading overview • Working with the Dispatcher • Async calling patterns • Begin/End and Async/Completed • Task Parallel Library / PFX / PLINQ • Task-based Async Pattern (Async CTP) • Reactive Extensions

25. Reactive Extensions (Rx) • AKA LINQ to Events • Available now as add-ons • .NET Framework, Silverlight, SL for Windows Phone, JavaScript • Allows you to treat events and async operations as collections • Allows use of LINQ operations to logically filter, join, order, etc

26. Reactive Extensions • IObservable<T> / IObserver<T> interfaces • Duals of IEnumerable<T> / IEnumerator<T> • Allows LINQ syntax • You provide an IObserver implementation that handles • OnNext – the next event occurred • OnCompleted – Events or async operation is done • OnError – exception handling • Clean API for events and async ops • Things that are inherently a chain of asynchronously produced data that you want to consume

27. Reactive Extensions (Rx) Brian Noyes Chief Architect IDesign Inc. (www.idesign.net) demo

28. What Should I Use? • Near term: • Async/Completed if you want cleanest/safest/easiest code • TPL if you want to start moving into the Task-based world • Rx for combining multiple asynchronous sources • PLINQ/Parallel for parallel collection processing • Sightly longer term: • Primarily Task-based Async Pattern • Secondarily Rx for compositional scenarios • PLINQ/Parallel for parallel collection processing

29. Resources • DEV324 | C# and Visual Basic Future: Async Made Simple – Alex Turner, Wed May 18 3:15 pm • Deeper dive into Task-based Async Pattern • Programming .NET Components, 2nd Edition, Juval Lowy, O’Reilly & Assoc.http://oreilly.com/catalog/9780596102074 • Reactive Extensionshttp://msdn.microsoft.com/en-us/devlabs/gg577609 • Async CTPhttp://msdn.microsoft.com/en-us/vstudio/gg316360 E-mail: brian.noyes@idesign.net Blog: http://briannoyes.net Twitter: @briannoyes

30. Web Track Resources • http://www.asp.net/ • http://www.silverlight.net/ • http://www.microsoft.com/web/gallery/ • http://www.iis.net/ • http://weblogs.asp.net/Scottgu/ • http://www.hanselman.com/blog/

31. Resources • Connect. Share. Discuss. http://northamerica.msteched.com Learning • Sessions On-Demand & Community • Microsoft Certification & Training Resources www.microsoft.com/teched www.microsoft.com/learning • Resources for IT Professionals • Resources for Developers • http://microsoft.com/technet • http://microsoft.com/msdn

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