This document discusses asynchronous (async) programming in C#. It begins by explaining what async programming is and how it allows applications to be more responsive and scalable by freeing threads to handle other requests. It then provides various examples of how to write async methods using the async and await keywords. It discusses important best practices like avoiding async void methods and using ConfigureAwait(false). Finally, it mentions some useful tools for async programming like Task.WhenAll and parallel programming APIs.

1. Async Programming
Darío Kondratiuk
Autor de Puppeteer-Sharp
@kblok - @hardkoded
www.hardkoded.com
De 0 a Task.IsComplete

2. Async Programming

6. var state = DownloadAsync().Result;
var state = DownloadAsync().GetAwaiter().GetResult();

7. var state = DownloadAsync().Wait();
var state = DownloadAsync().GetAwaiter().GetResult();

8. var state = DownloadAsync().GetAwaiter().GetResult();
var state = await DownloadAsync();

9. var state = await DownloadAsync();
var state = await DownloadAsync().ConfigureAwait(false);

10. var state = await DownloadAsync().ConfigureAwait(false);
return DownloadAsync();

12. Qué es Async?

13. Qué es Async?

14. Stephen Cleary

17. Concurrencia
Multi-Threading
Parallel Processing
Async Programming
Reactive
Programming

18. No es acerca de ser rápido
Sino de hacer más

19. UI Responsive

20. Más requests en el server

21. Escalabilidad

22. [HttpGet]
public string Get()
{
Task.Delay(500).GetAwaiter().GetResult();
Task.Delay(500).GetAwaiter().GetResult();
return "Foo";
}

23. [HttpGet]
public async Task<string> Get()
{
await Task.Delay(500);
await Task.Delay(500);
return "Foo";
}

24. Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 4 --timeout 2s https://localhost:5001/api/values
Running 30s test @ https://localhost:5001/api/values
4 threads and 4 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.13s 84.02ms 1.43s 78.64%
Req/Sec 0.00 0.00 0.00 100.00%
103 requests in 30.07s, 15.59KB read
Requests/sec: 3.42
Transfer/sec: 530.84B
Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 4 --timeout 2s https://localhost:5001/api/valuesasync
Running 30s test @ https://localhost:5001/api/valuesasync
4 threads and 4 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.09s 81.10ms 1.42s 83.18%
Req/Sec 0.00 0.00 0.00 100.00%
107 requests in 30.10s, 16.20KB read
Requests/sec: 3.55
Transfer/sec: 550.98B

25. Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 10 --timeout 2s https://localhost:5001/api/values
Running 30s test @ https://localhost:5001/api/values
4 threads and 10 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.27s 178.19ms 1.99s 65.54%
Req/Sec 1.69 1.86 10.00 89.16%
179 requests in 30.10s, 27.09KB read
Socket errors: connect 0, read 0, write 0, timeout 2
Requests/sec: 5.95
Transfer/sec: 0.90KB
Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 10 --timeout 2s https://localhost:5001/api/valuesasync
Running 30s test @ https://localhost:5001/api/valuesasync
4 threads and 10 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.09s 70.54ms 1.52s 90.14%
Req/Sec 4.07 4.07 10.00 43.59%
213 requests in 30.10s, 32.24KB read
Requests/sec: 7.08
Transfer/sec: 1.07KB

26. Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 20 --timeout 2s https://localhost:5001/api/values
Running 30s test @ https://localhost:5001/api/values
4 threads and 20 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.58s 200.81ms 2.00s 62.65%
Req/Sec 5.18 5.40 29.00 93.58%
247 requests in 30.06s, 37.53KB read
Socket errors: connect 0, read 0, write 0, timeout 81
Requests/sec: 8.22
Transfer/sec: 1.25KB
Darios-MBP:AsyncProgrammingWeb neo$ wrk -d 30s -t 4 -c 20 --timeout 2s https://localhost:5001/api/valuesasync
Running 30s test @ https://localhost:5001/api/valuesasync
4 threads and 20 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 1.73s 143.07ms 2.00s 64.51%
Req/Sec 3.62 2.98 10.00 79.08%
320 requests in 30.06s, 48.73KB read
Socket errors: connect 0, read 0, write 0, timeout 27
Requests/sec: 10.64
Transfer/sec: 1.62KB

27. Async

28. [HttpGet]
public async Task<string> GetAsync()
{
await Task.Delay(500);
await Task.Delay(500);
return "Foo";
}
Task es Async
Task es Awaitable
Son promesas

29. await - demo

30. Un método async va a
correr sincronico hasta el
primer await

31. Un método async va a
correr sincronico hasta el
primer await con una
Task incompleta

34. Qué es await?

35. Qué es await?
Es syntax sugar

36. private static Task LogAsync(int number)
=> Console.Out.WriteLineAsync($"Waiting for {(int) number}");

37. private static Task LongAsync(int number)
{
<LongAsync>d__4 stateMachine = new <LongAsync>d__4 {
number = number,
<>t__builder = AsyncTaskMethodBuilder.Create(),
<>1__state = -1
};
stateMachine.<>t__builder.Start<<LongAsync>d__4>(ref stateMachine);
return stateMachine.<>t__builder.get_Task();
}

38. await
The good part

39. await, the good part
Syntax sugar

40. AggregateException
try
{
await task;
}
catch (Exception ex)
{
}

41. Entendiendo mandamientos

42. Entendiendo mandamientos
async void

43. Entendiendo mandamientos
Task.Result

44. Entendiendo mandamientos
await vs return Task

45. Synchronization Context

46. Synchronization Context
Cada Thread tiene un
Synchronization Context

47. Synchronization Context
En cada await el Context es capturado

48. Synchronization Context
Varía por plataforma

49. Synchronization Context
UI Synchronization Context y el
UI Thread

50. Synchronization Context
AspNetSyncronizationContext y
HttpContext.Current

51. Synchronization Context
Sin Synchronization Context y el
ThreadPool

52. Entendiendo mandamientos

53. Entendiendo mandamientos
.ConfigureAwait(false);

54. Herramientas Útiles

55. Herramientas Útiles
Task.FromResult

56. Herramientas Útiles
Task.WhenAll

57. Herramientas Útiles
Task.WhenAny

58. Herramientas Útiles
TaskCompletionSource

59. Parallel Programming
● Task.Run
● Parallel Class
○ Parallel.For
○ Parallel.ForEach
○ Parallel.Invoke
● PLINQ (AsParallel)
● DataFlow

60. Palabras finales

61. El poder de una estrella

62. ● https://www.meetup.com/Net-Baires/
● https://net-latam.slack.com

63. Links
● https://github.com/kblok/async-programming-talk
● https://github.com/kblok/puppeteer-sharp
● https://www.hardkoded.com
● http://www.hardkoded.com/blog/async-void-fairy-tale
● https://blog.stephencleary.com/
● Concurrency in C# Cookbook, O’Reilly
● Async in C# 5, O’Reilly
● Pro Asynchronous Programming with .NET, APress

64. Gracias!