Cole Durdan

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

 “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------|

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

 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

 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(); }

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); } }

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

 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

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

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; }

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

async Task AccessTheWebAsync() { HttpClient client = new HttpClient(); Task getStringTask = client.GetStringAsync(" DoIndependentWork(); string urlContents = await getStringTask; return urlContents.Length; }

Source:

  5-worth-the-await.aspx 5-worth-the-await.aspx  asynchronous-methods-in-aspnet-45 asynchronous-methods-in-aspnet-45   Programming-in-Csharp-5-0-using-async Programming-in-Csharp-5-0-using-async

 Asynchronous ◦ Multi-Threaded