Joe Hummel, PhD Microsoft MVP Visual C++ Technical Staff: Pluralsight, LLC Adjunct Professor: U. of Illinois, Chicago and Loyola University Chicago stuff:

 Motivation  Execution model  Parallel programming with Tasks  Parallel programming with Async / Await  Demos 2

3  Async programming:  Better responsiveness…  GUIs (desktop, web, mobile)  Cloud  Windows 8  Parallel programming:  Better performance…  Engineering  Oil and Gas  Pharma  Science  Social media Disk and network I/O number crunching and big data processing

4 C C C C C C C C Main thread C Main > if… while… Main > if… while… Task Stmt1; Stmt2; Stmt3; Task Stmt1; Stmt2; Stmt3; Main > if… while… Main > if… while… Task1 Stmt1; Stmt2; Stmt3; Task1 Stmt1; Stmt2; Stmt3; Task2 Stmt4; Stmt5; Stmt6; Task2 Stmt4; Stmt5; Stmt6; Worker thread Main thread Threads share, run asynchr onously Threads run in parallel  Single core:  Multicore:

 Threads(.NET 1.0)  Async Delegates  QueueUserWorkItem  BackgroundWorker  Task Parallel Library(.NET 4.0)  Async / Await(.NET 4.5) 5 Easier…

 Mandelbrot set… 6

 Programming model based on concept of a Task 7 Task == a unit of work; an object denoting an ongoing operation or computation.

8 Windows Process (.NET) App Domain App Domain App Domain App Domain App Domain App Domain.NET Thread Pool worker thread worker thread worker thread worker thread Parallel.For(... ); task global work queue Task Parallel Library Resource Manager Task Scheduler Windows

 Asian options financial modeling… 9

10 void button1_Click(…) { var uictx = // grab UI thread context to run UI task: TaskScheduler.FromCurrentSynchronizationContext(); Task.Factory.StartNew(()=> { return DoLongLatencyOp(); } ).ContinueWith((antecedent) => { lstBox.Items.Add(antecedent.Result); }, uictx // execute this task on UI thread: ); } void button1_Click(…) { var uictx = // grab UI thread context to run UI task: TaskScheduler.FromCurrentSynchronizationContext(); Task.Factory.StartNew(()=> { return DoLongLatencyOp(); } ).ContinueWith((antecedent) => { lstBox.Items.Add(antecedent.Result); }, uictx // execute this task on UI thread: ); } void button1_Click(…) { var result = DoLongLatencyOp(); lstBox.Items.Add(result); } void button1_Click(…) { var result = DoLongLatencyOp(); lstBox.Items.Add(result); }

11 void button1_Click(…) { var result = DoLongLatencyOp(); lstBox.Items.Add(result); } void button1_Click(…) { var result = DoLongLatencyOp(); lstBox.Items.Add(result); } async void button1_Click(…) { var result = await Task.Run(() => DoLongRunningOp()); lstBox.Items.Add(result); } async void button1_Click(…) { var result = await Task.Run(() => DoLongRunningOp()); lstBox.Items.Add(result); } Method *may* perform async, long- latency op Tells compiler to setup a continuation to execute rest of method --- ON SAME THREAD CONTEXT --- and then returns from method so it doesn’t wait.

 await must wait on a task ◦ implies underlying method must create & start a task… 12 async void button1_Click(…) { var result = await Task.Run(() => DoLongRunningOp()); lstBox.Items.Add(result); } async void button1_Click(…) { var result = await Task.Run(() => DoLongRunningOp()); lstBox.Items.Add(result); } System.IO.FileStream file =...; int read = await file.ReadAsync(buffer, offset, count); System.IO.FileStream file =...; int read = await file.ReadAsync(buffer, offset, count);

 Think chunky, not chatty ◦ i.e. designed for coarse-grain, long-latency operations ◦ file I/O, network I/O, compute-bound work…  Think APIs exposing “TAP” pattern ◦ designed to take advantage of Task-based Asynchronous Pattern

 Async web calls are a classic use-case 14 private byte[] GetURLContents(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = webReq.GetResponse()) { using (Stream responseStream = response.GetResponseStream()) { responseStream.CopyTo(content); } return content.ToArray(); } private byte[] GetURLContents(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = webReq.GetResponse()) { using (Stream responseStream = response.GetResponseStream()) { responseStream.CopyTo(content); } return content.ToArray(); } Synchronous Version data = GetURLContents(“...”); // call and prepare to wait:

15 private async Task GetURLContentsAsync(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = await webReq.GetResponseAsync()) { using (Stream responseStream = response.GetResponseStream()) { await responseStream.CopyToAsync(content); } return content.ToArray(); } private async Task GetURLContentsAsync(string url) { var content = new MemoryStream(); var webReq = (HttpWebRequest)WebRequest.Create(url); using (WebResponse response = await webReq.GetResponseAsync()) { using (Stream responseStream = response.GetResponseStream()) { await responseStream.CopyToAsync(content); } } return content.ToArray(); } Asynchronous Version data = await GetURLContentsAsync(“...”); // call, start, don’t wait: Synchronous Version

 Asynchronous web requests… 16

 Return a task for caller to await upon… 17 public int SomeOperation(...) { int result; result =...; return result; } public int SomeOperation(...) { int result; result =...; return result; } public Task SomeOperationAsync(...) { return Task.Run ( () => { int result; result =...; return result; } ); } public Task SomeOperationAsync(...) { return Task.Run ( () => { int result; result =...; return result; } ); }

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 Thread-based execution model at the bottom  Task-based execution model on top  For Performance: ◦ Prefer Task Parallel Library  For Responsiveness: ◦ Prefer Async / Await 19

 Presenter: Joe Hummel ◦ ◦ Materials:  For more info: ◦ MSDN Magazine, October 2011 (3 articles): 1.“Easier Asynchronous Programming with the New Visual Studio Async CTP” 2.“Pause and Play with Await” 3.“Async Performance: Understanding the Costs of Async and Await” 20