End to-end async and await

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  • Have been in Tampa for almost 2 months. Excited to be here and looking forward to engaging with the community. We have built very strong successful relationships with many Fortune 1000/500/1 clients in our other cities.
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  • End to-end async and await

    1. 1. End-to-End Async and Await Vince Fabro Cardinal Solutions Practice Manager, Enterprise App Dev @vfabro
    2. 2. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    3. 3. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    4. 4. What is Async? • C# 5.0 and .NET 4.5 • async and await keywords • Asynchronous programming for the masses!
    5. 5. What is Async? • Asynchronous == Parallel? • Asynchronous == Multithreaded? • Asynchronous == Easy?
    6. 6. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    7. 7. Why bother? • Improve app responsiveness • Simplify asynchronous programming  more approachable Simpler / More approachable than what?
    8. 8. Asynchrony the good old way • [… as opposed to the much worse older ways] • APM and EAP • APM – Asynchronous Programming Model – http://msdn.microsoft.com/en-us/library/ms228963%28v=vs.110%29.aspx – http://msdn.microsoft.com/en-us/magazine/cc163467.aspx • EAP – Event-based Asynchronous Pattern – http://msdn.microsoft.com/en-us/library/wewwczdw%28v=vs.110%29.aspx
    9. 9. Asynchronous Programming Model IAsyncResult result = Dns.BeginGetHostEntry( args[0], null, null); // Poll for completion information. while (result.IsCompleted != true) { … } // EndGetHostByName blocks until complete. IPHostEntry host = Dns.EndGetHostEntry(result); string[] aliases = host.Aliases; .NET2.0+
    10. 10. Event-based Asynchronous Pattern private SoundPlayer player; private void InitializeSound() { // Create an instance of the SoundPlayer class. player = new SoundPlayer(); // Listen for the LoadCompleted event. player.LoadCompleted += new AsyncCompletedEventHandler(player_LoadCompleted); player.SoundLocation = filepathTextbox.Text; player.Play(); } private void player_LoadCompleted( object sender, AsyncCompletedEventArgs e) { } .NET2.0+
    11. 11. Supplanted by the TPL • Both APM and EAP  – “This pattern is no longer recommended for new development” • TPL  Task Parallel Library – http://msdn.microsoft.com/en- us/library/dd460693%28v=vs.110%29.aspx .NET4.0+
    12. 12. Supplanted by the TPL .NET4.0+
    13. 13. Supplanted by the TPL .NET4.0+
    14. 14. Supplanted by the TPL Parallel.ForEach(sourceCollection, item => Process(item)); Parallel.Invoke(() => DoSomeWork(), () => DoSomeOtherWork()); // Create a task and supply a user delegate Task taskA = new Task( () => Console.WriteLine("Hello from taskA.")); // Start the task. taskA.Start(); // Output a message from the calling thread. Console.WriteLine("Hello from thread '{0}'.", Thread.CurrentThread.Name); taskA.Wait(); .NET4.0+
    15. 15. The New Hotness! • TAP – Task-based Asynchronous Pattern • async and await • So… Why bother? – Simpler than APM and EAP – Simpler than raw TPL Builds on the TPL .NET4.5
    16. 16. Task-based Asynchronous Pattern private async Task<int> AccessTheWebAsync() { HttpClient client = new HttpClient(); string urlContents = await client.GetStringAsync( "http://msdn.microsoft.com"); return urlContents.Length; }
    17. 17. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    18. 18. How does this work?
    19. 19. Task-based Asynchronous Pattern private async Task<int> AccessTheWebAsync() { HttpClient client = new HttpClient(); string urlContents = await client.GetStringAsync( "http://msdn.microsoft.com"); return urlContents.Length; } 1. Before await 2. Await Task 3. Post await 2. “Awaitable” 3. Continuation 0. For compiler
    20. 20. How does this work?
    21. 21. Gimme the Code! void IAsyncStateMachine.MoveNext() { string result = null; try { int num = state; //if (!Stop) if (num != -3) { TaskAwaiter<string> taskAwaiter; // Machine starts with num=-1 so we enter if (num != 0) { // First (+ initial) state code, run code before await is invoked httpClient = new HttpClient(); Debug.WriteLine("before await"); // A task is invoked taskAwaiter = httpClient.GetStringAsync(url).GetAwaiter();
    22. 22. Gimme the Code! Whole Lotta Code!
    23. 23. How does it work? • Generates a state machine for every async call • SynchronizationContext • Continuation Tasks
    24. 24. How does it work? • SynchronizationContext – Provides a way to queue a unit of work to a context, not to a specific thread – Keeps a queue and count of work to do – Every thread has a current context – http://msdn.microsoft.com/en-us/magazine/gg598924.aspx
    25. 25. How does it work? • SynchronizationContext Implementations: – WindowsFormsSynchronizationContext – DispatcherSynchronizationContext • WPF and SilverLight – WinRTSynchronizationContext – AspNetSynchronizationContext • ASP.NET thread pool – Default SynchronizationContext • ThreadPool
    26. 26. How does it work? • Continuation Tasks – On completion of one task, invoke another // The antecedent task. Can also be created with Task.Factory.StartNew. Task<DayOfWeek> taskA = new Task<DayOfWeek>(() => DateTime.Today.DayOfWeek); // The continuation. Its delegate takes the antecedent task // as an argument and can return a different type. Task<string> continuation = taskA.ContinueWith((antecedent) => { return String.Format("Today is {0}.", antecedent.Result); }); // Start the antecedent. taskA.Start(); // Use the contuation's result. Console.WriteLine(continuation.Result);
    27. 27. Task-based Asynchronous Pattern private async Task<int> AccessTheWebAsync() { HttpClient client = new HttpClient(); string urlContents = await client.GetStringAsync( "http://msdn.microsoft.com"); return urlContents.Length; } 1. Before await 2. Await Task 3. Post await 2. “Awaitable” 3. Continuation 0. For compiler
    28. 28. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    29. 29. Gotchas… • Requirements – You must use the async keyword to await – void events may need marked with async public void Blah  public async Task BlahAsync • Limitations – You cannot declare ref or out parameters on an async method
    30. 30. Gotchas… • When you can’t await async methods – Inside catch and finally blocks – Inside properties – Inside a lock block – In an unsafe region – Within most portions of a LINQ query
    31. 31. Gotchas… • Deadlock and Race conditions, oh my! var delayTask = DelayAsync(); delayTask.Wait();
    32. 32. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices & More Details • Next Steps
    33. 33. Best Practices & More Details • Name async methods BlahBlahAsync • End to end – Cascading Async
    34. 34. Best Practices & More Details • Configuring ASP.NET – Increase App Pool’s queue limit – AsyncTimeout • Async in ASP.NET page lifecycle events %@Page ... Async=“true” % RegisterAsyncTask( new PageAsyncTask(GetDataAsync)); http://www.asp.net/mvc/tutorials/mvc-4/using-asynchronous-methods-in-aspnet-mvc-4 http://www.asp.net/web-forms/tutorials/aspnet-45/using-asynchronous-methods-in-aspnet-45
    35. 35. Best Practices & More Details • Unit testing – You can test async methods [TestMethod] public async Task GivenBlah…() { var result = await testClass.DoSomethingAsync(); } – You can mock async method calls mockDownloadContent.Setup(x => x.DoSomethingAsync()) .Returns(Task.FromResult<string>(expectedResult));
    36. 36. Best Practices & More Details • Entity Framework 6 – ApplicationDbContext await context.Categories.Include( c => c.Products).LoadAsync(); int savedCount = await context.SaveChangesAsync(); – QueryableExtensions var employeeCount = await query.CountAsync(); var firstEmployee = await query.FirstAsync(); https://entityframework.codeplex.com/wikipage?title=Task-based%20Asynchronous%20Pattern%20support%20in%20EF
    37. 37. Best Practices & More Details • Executing tasks in parallel await Task1Async(); await Task2Async(); await Task3Async(); await Task.WhenAll(Task1Async(), Task2Async(), Task3Async());
    38. 38. Best Practices & More Details • Death by a thousand cuts – Batch up async calls • ConfigureAwait(false) http://msdn.microsoft.com/en-us/magazine/hh456402.aspx
    39. 39. Best Practices & More Details • await Task.Yield() http://msdn.microsoft.com/en-us/library/hh873173%28v=vs.110%29.aspx • Task cancellation http://msdn.microsoft.com/en-us/library/jj155759.aspx • Reporting progress http://simonsdotnet.wordpress.com/2013/10/11/updating-your-ui-asynchronously- part-3-reporting-progress/
    40. 40. Agenda • What is Async? • Why bother? • How does this work? • Gotchas • Best Practices • Next Steps
    41. 41. References • Asynchronous Programming Patterns – http://msdn.microsoft.com/en-us/library/wewwczdw%28v=vs.110%29.aspx • Async and await FAQ • Steven Cleary’s blog • Channel 9 • Stephen Toub: The Costs of Async – http://msdn.microsoft.com/en-us/magazine/hh456402.aspx
    42. 42. Thank You!

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