Deceptive simplicity of async and await
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The document discusses the deceptive simplicity of using async and await in programming, highlighting potential application errors and UI thread issues. It covers various coding practices, including proper method definitions and the limitations of async methods. The document concludes with essential tips for using async/await effectively and refers to additional resources on the topic.
![Deep dive
Deceptive simplicity of async and await
static void Main(string[] args)
{
DoSomething();
}
static void DoSomething()
{
// method body
}
static void Main(string[] args)
{
DoSomething();
}
async static Task DoSomething()
{
// method body
}](https://image.slidesharecdn.com/asyncawait-130602212609-phpapp02/85/Deceptive-simplicity-of-async-and-await-9-320.jpg)
Deceptive simplicity of async and await
- 1. Deceptive simplicity of async and await WIN387 Andrei Marukovich lunarfrog.com @amarukovich
- 2. Looks familiar? Deceptive simplicity of async and await
- 3. • Application errors • Using the UI thread for performing long operations UI unresponsiveness Deceptive simplicity of async and await
- 4. Deceptive simplicity of async and await Synchronous method private void ButtonClick(object sender, EventArgs e) { WebClient client = new WebClient(); var imageData = client.DownloadData(“http://image-url”); pictureBox.Image = Image.FromStream(new MemoryStream(imageData)); }
- 5. Deceptive simplicity of async and await Asynchronous method private async void ButtonClick(object sender, EventArgs e) { WebClient client = new WebClient(); var imageData = await client.DownloadDataTaskAsync(“http://image-url”); pictureBox.Image = Image.FromStream(new MemoryStream(imageData)); }
- 6. Deceptive simplicity of async and await Asynchronous method private async void ButtonClick(object sender, EventArgs e) { WebClient client = new WebClient(); var imageData = await client.DownloadDataTaskAsync(“http://image-url”); pictureBox.Image = Image.FromStream(new MemoryStream(imageData)); var strData = await client.DownloadStringTaskAsync(“http://str-url”); // … }
- 7. Every API which might take more than 50ms should be async WinRT Deceptive simplicity of async and await
- 8. Deceptive simplicity of async and await Demo WinRT and async
- 9. Deep dive Deceptive simplicity of async and await static void Main(string[] args) { DoSomething(); } static void DoSomething() { // method body } static void Main(string[] args) { DoSomething(); } async static Task DoSomething() { // method body }
- 10. Deep dive Deceptive simplicity of async and await
- 11. State machine Deceptive simplicity of async and await struct DoSomethingStruct : IAsyncStateMachine { // Argument and local variables public Int32 x; // Compiler-generated variables public Int32 _state; public AsyncTaskMethodBuilder _builder; void MoveNext() { … } }
- 12. MoveNext() Deceptive simplicity of async and await void MoveNext() { try { switch(_state) { // modified method body } } catch (Exception exception) { _builder.SetException(exception); return; } _builder.SetResult(); }
- 13. Async function transformation Deceptive simplicity of async and await static Task DoSomething() { var stateMachine = new DoSomethingStruct(); stateMachine._builder = AsyncTaskMethodBuilder.Create(); stateMachine._state = -1; stateMachine._builder.Start(stateMachine); return stateMachine._builder.Task; }
- 14. Using await Deceptive simplicity of async and await await DoSomething(); Task task = DoSomething(); INotifyCompletion awaiter = task.GetAwaiter(); if (!awaiter.IsCompleted) { awaiter.OnCompleted(continue_delegate) }
- 15. Bringing it all together async Task Method1() { await Method2(); } async Task Method2() { await _file.CopyAsync(_folder, _name); }
- 16. Bringing it all together Method1 Method2 Task CopyAsync Copy Task Method2 Method1
- 17. Defining async methods async Task Method1() { } async Task<StorageFolder> Method2() { return ApplicationData.Current.LocalFolder; } async void button1_Click(object sender, EventArgs e) { }
- 18. Avoid async void as much as possible Deceptive simplicity of async and await
- 19. Demo async void and error handling Deceptive simplicity of async and await
- 20. async lambdas obj.Handle( async () => { await Task.Delay(1000); } ); Deceptive simplicity of async and await void Handle(Func<Task> action); Func<Task> f = async () => { await Task.Delay(1000); } void Handle(Action action); Action a = async () => { await Task.Delay(1000); } IL: AsyncTaskMethodBuilder IL: AsyncVoidMethodBuilder
- 21. Demo More async in WinRT Deceptive simplicity of async and await
- 22. Constrains • Cannot use await inside constructor and property accessor • Cannot use await inside catch and finally • Cannot use await inside lock block • Cannot use await inside Main method • An async method cannot have a ref or out parameters
- 23. What to take away • async/await are not magic • Always await your async operations • async void methods are only suited for UI event handlers • Be careful around async void and exceptions • Be aware of deferral classes in WinRT
- 24. Next steps • Parallel Programming team blog http://bit.ly/pfxteam • Deeper into Async and Await, Kathleen Dollard ARC319 • Three Essential Tips for Async (video) http://bit.ly/AsyncTips • Async for .NET 4.0 and Windows Phone (NuGet) http://bit.ly/AsyncNet4