POINT OF FAILURES TOPICS .NET. msdn

Transcription

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2 TOPICS POINT OF FAILURES msdn.net 2

3 THREADS TASKS msdn.net 3

4 KEY FEATURES msdn.net 4

5 TASK CREATION var task = new Task(Func<TResult> func); task.start(); //... task.wait(); var task = Task.Run(Func<TResult> func); //... task.wait(); var task = Task.Factory.StartNew(Func<TResult> func); //... task.wait(); 5

6 TASK COMPLETION SOURCE Psychic Debugging of Async Methods public Task<int> SomeLibraryMethodAsync() var tcs = new TaskCompletionSource<int>(); Task.Factory.StartNew(() => try int result = SomeLibraryMethod(); tcs.setresult(result); catch (Exception e) // Bug! tcs.setexception(e); ); return tcs.task; 6

7 ASYNC/AWAIT 7

8 ASYNC AWAIT private static async Task GetHttpResponseAsync() using (var httpclient = new HttpClient()) var responsetask = httpclient.getasync(" // Do independent work... var response = await responsetask; Console.WriteLine(response.Headers); 8

9 PROS private static async Task GetHttpResponseAsync() using (var httpclient = new HttpClient()) var responsetask = httpclient.getasync(" // Do independent work... var response = await responsetask; Console.WriteLine(response.Headers); 9

10 CONS 1 2 private static async Task GetHttpResponseAsync() using (var httpclient = new HttpClient()) 3 var responsetask = httpclient.getasync(" // Do independent work var response = await responsetask; Console.WriteLine(response.Headers); 6 Async and Await (msdn) public async HttpResponseMessage GetAsync(string url) 10

11 private static async Task GetHttpResponseAsync() using (var httpclient = new HttpClient()) var responsetask = httpclient.getasync(" // Do independent work... var response = await responsetask; Console.WriteLine(response.Headers); 11

12 [AsyncStateMachine(typeof(<GetHttpResponseAsync>d 1)), DebuggerStepThrough] private static Task GetHttpResponseAsync() <GetHttpResponseAsync>d 1 statemachine = new <GetHttpResponseAsync>d 1 <>t builder = AsyncTaskMethodBuilder.Create(), <>1 state = -1 ; statemachine.<>t builder.start<<gethttpresponseasync>d 1>(ref statemachine); return statemachine.<>t builder.task; [CompilerGenerated] private sealed class <GetHttpResponseAsync>d 1 : IAsyncStateMachine Behind the.net 4.5 Async Scene 12

13 ASYNC VOID private async void ThrowExceptionAsync() throw new InvalidOperationException(); public void CallThrowExceptionAsync() try ThrowExceptionAsync(); catch (Exception) Console.WriteLine("Failed"); 13

14 For goodness sake stop using async void 14

15 ASYNC LAMBDA var secs = Time(() => Thread.Sleep(1000); ); Console.WriteLine($"Seconds: secs:f6"); Seconds: Seconds: Seconds: var secs2 = Time(async () => await Task.Delay(1000); ); Console.WriteLine($"Seconds: secs2:f6"); public static double Time(Action action) public static double Time(Func<Task> func) 15

16 ASYNC LAMBDA var t = Task.Factory.StartNew(() => Thread.Sleep(1000); return 42; ); var u = Task.Factory.StartNew(async () => await Task.Delay(1000); return 42; ).Unwrap(); Passing async lambdas 16

17 private async Task WorkThenWait() await Task.Yield(); Thread.Sleep(1000); Console.WriteLine("work"); await Task.Delay(1000); work started started work completed Asynchronous gotchas in C# public void Demo() var child = WorkThenWait(); Console.WriteLine("started"); child.wait(); Console.WriteLine("completed"); 17

18 Don't Block on Async Code public class MyController : ApiController private static async Task<JObject> GetJsonAsync(Uri uri) using (var client = new HttpClient()) var jsonstring = await client.getstringasync(uri); return JObject.Parse(jsonString); public async Task<string> GetAsync() var json = await GetJsonAsync(new Uri(" return json.tostring(); 18

19 class Accumulator private int m_sum = 0; public int Sum => m_sum; 4 6 Don't mix await and compound assignment public async Task Add(Task<int> value) var temp = await value; m_sum += temp; await value; var task1 = acc.add(tcs1.task); var task2 = acc.add(tcs2.task); tcs1.setresult(2); tcs2.setresult(4); await task1; await task2; Console.WriteLine(acc.Sum); 19

20 Don t forget to complete your Tasks! Watch out for Signatures! Be aware of your Synchronization context! Think double, less trouble... 20

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