This document contains the agenda and slides for a talk titled "Xamarin Talks #1" given by Paulo Morgado. The talk discusses best practices for asynchronous programming using async and await in C#, including only using async void for event handlers, determining whether a task is CPU-bound or I/O-bound, using Task.Run appropriately, avoiding deadlocks, using ConfigureAwait(false), and caching returned tasks. The slides provide code examples and explanations to illustrate the concepts.

1. Lisbon, May 30th 2015
await Xamarin()
PTXug - Xamarin Talks #1

2. Speaker
http://PauloMorgado.NET/
http://about.me/PauloMorgado
http://www.slideshare.net/PauloJorgeMorgado
http://pontonetpt.org/blogs/paulomorgado/
http://blogs.msmvps.com/paulomorgado/
http://weblogs.asp.net/paulomorgado
http://www.revista-programar.info/author/pmorgado/
C:> ping me @paulomorgado

3. Agenda

4. For goodness’ sake, stop
using async void!

5. async void is only for event handlers

6. Events are not going away.

7. async over events

8. Is it CPU-bound,
or I/O-bound?

9. Thread pool

10. Don’t lie

11. Two ways of thinking about asynchrony
Foo(); var task = FooAsync();
From the method signature (how people call it)
void Foo()
{
for (int i=0; i<100; i++)
Math.Sin(i);
}
From the method implementation (what resources it uses)
async Task FooAsync()
{
await client.DownloadAsync();
}

12. Async methods: Your caller’s assumptions
Is this true for your async methods?

13. Libraries shouldn’t use
Task.Run()

14. Your callers should be the ones to call Task.Run
synchronous block the current thread
asynchronous without spawning new threads

15. Sync methods: Your caller’s assumptions
void Foo() { FooAsync().Wait(); } -- will deadlock!!!

16. Task.Run() is the way to
create new tasks

17. Task creation

18. await all the way

19. await all the way

20. Use ConfigureAwait(false)

21. SynchronizationContext

22. SynchronizationContext and await

23. SynchronizationContext: ConfigureAwait

24. Use the CancellationToken

25. Use the CancellationToken

26. Cache the returned
Task<T>

27. Library perf considerations

28. Q & A

29. References
http://blogs.msdn.com/b/lucian/archive/2013/11/23/talk-mvp-summit-async-best-practices.aspx
http://channel9.msdn.com/Series/Three-Essential-Tips-for-Async/Three-Essential-Tips-For-Async-
Introduction
http://curah.microsoft.com/45553/asyncawait-general
http://curah.microsoft.com/44400/async-and-aspnet
https://github.com/paulomorgado/xamarin-xamarin-store-app

30. Sponsors

31. C:> ping me @paulomorgado