1. Cole Durdan

2.  What is asynchronous programming?  Previous patterns  Task Based Async Programming .NET 4.5 Keywords  What happens in an async. method?  Demo

3.  “Asynchronous” means API does not block calling thread  Multithreading? ◦ Not Necessarily  Doesn’t lock UI on large computations Synchronous: |----A-----| |-----B-----------| |-------C------| Asynchronous: |----A-----| |-----B-----------| |-------C------|

4.  Web Access  Database Requests  Working with files  Working with images  WCF programming  Working with sockets  With UI that need to be responsive

5.  The Asynchronous Programming Model (APM) ◦ BeginMethodName and EndMethodName ◦ IAsyncResult ◦ Keep track of states  The Event based Asynchronous Pattern (EAP) ◦ Assigns delegates to event handlers that are invoked when an event is triggered ◦ introduced in the.NET Framework version 2.0

6.  public static IAsyncResult BeginCopyTo(Stream source, Stream destination) { var tcs = new TaskCompletionSource(); byte[] buffer = new byte[0x1000]; Action readWriteLoop = null; readWriteLoop = iar => { try { for (bool isRead = iar == null; ; isRead = !isRead) { switch (isRead) { case true: iar = source.BeginRead(buffer, 0, buffer.Length, readResult => { if (readResult.CompletedSynchronously) return; readWriteLoop(readResult); }, null); if (!iar.CompletedSynchronously) return; break; case false: int numRead = source.EndRead(iar); if (numRead == 0) { tcs.TrySetResult(true); return; } iar = destination.BeginWrite(buffer, 0, numRead, writeResult => { try { if (writeResult.CompletedSynchronously) return; destination.EndWrite(writeResult); readWriteLoop(null); } catch(Exception e) { tcs.TrySetException(e); } }, null); if (!iar.CompletedSynchronously) return; destination.EndWrite(iar); break; } } } } catch(Exception e) { tcs.TrySetException(e); } }; readWriteLoop(null); return tcs.Task; } public static void EndCopyTo(IAsyncResult asyncResult) { ((Task)asyncResult).Wait(); }

7. public static async void CopyToAsync(Stream source, Stream destination) { byte[] buffer = new byte[0x1000]; int numRead; while((numRead = await source.ReadAsync(buffer, 0, buffer.Length)) > 0) { await destination.WriteAsync(buffer, 0, numRead); } }

8.  A lot of extra code  Difficult to… ◦ Read ◦ Write ◦ Maintain ◦ Debug

9.  Relies on the Task Parallel Library (TPL)  System.Threading  System.Threading.Task namespace ◦ Introduced in.NET 4.0 Framework ◦ New support in 4.5  TPL is the preferred way to write multithreaded and parallel code

10.  Keywords ◦ “Async” ◦ “Await”  Return Type of Object Task ◦ Task if sub or void ◦ Task  Naming Convention ◦ MethodNameAsync()

11. Synchronous Method: int GetInt() { int number = GetNumber(); DoIndependentWork(); return number; } Asynchronous Method: async Task GetIntAsync() { Task getNumTask = GetNumberAsync(); DoIndependentWork(); int number = await getNumTask return number; }

12.  Mark async method with Async or async  Marked method can use Await or await

13. async Task AccessTheWebAsync() { HttpClient client = new HttpClient(); Task getStringTask = client.GetStringAsync("http://msdn.microsoft.com"); DoIndependentWork(); string urlContents = await getStringTask; return urlContents.Length; }

14. Source: http://msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx

15.  http://msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx http://msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx  http://blogs.msdn.com/b/dotnet/archive/2012/04/03/async-in-4- 5-worth-the-await.aspx http://blogs.msdn.com/b/dotnet/archive/2012/04/03/async-in-4- 5-worth-the-await.aspx  http://www.asp.net/web-forms/tutorials/aspnet-45/using- asynchronous-methods-in-aspnet-45 http://www.asp.net/web-forms/tutorials/aspnet-45/using- asynchronous-methods-in-aspnet-45  http://www.dotnetperls.com/async http://www.dotnetperls.com/async  http://www.codeproject.com/Tips/591586/Asynchronous- Programming-in-Csharp-5-0-using-async http://www.codeproject.com/Tips/591586/Asynchronous- Programming-in-Csharp-5-0-using-async

16.  Asynchronous ◦ Multi-Threaded