Slides used in Soft-Shake conference in Geneve, Switzerland October 2013

1. Welcome to an
asynchronous world!
Jose Luis Latorre
Geek, MVP, Writer, Speaker
Software engineer – UI Team Lead Developer
Roche Diagnostics

2. What will we see?
•
•
•
•
Where does Async evolves from?
ABC of Async & Await
Tasks &“The Flow”
How everything gets together in .NET
4.5
• Code!

3. Asynchronous programming is
becoming the norm in modern,
connected applications
(Anders Hejlsberg)

4. Synchronous versus
Asynchronous
var data = DownloadData(...);
ProcessData(data);
DownloadDataAsync(... , data =>
{
ProcessData(data);
});

5. Synchronous versus
Asynchronous
var data = DownloadData(...);
ProcessData(data);
DownloadDataAsync(... , data =>
{
ProcessData(data);
});

6. Asynchrony is…
about results that are delayed, and yielding
control while awaiting their results (co-operative
multitasking).
Good reasons to use asynchrony:
• for overall control / coordination structure of a
program
• for UI responsiveness
• for IO- and network-bound code

7. Trends
• Increasingly connected applications
– More latency
– More UI responsiveness problems
– More scalability issues
• Asynchronous programming
– Becoming the norm in responsive, scalable
apps
– Async-only APIs, e.g., Silverlight

8. A bit of evolution
C# + VB 4.5
Asynchronous
Programming
C# 4.0 + VB 10.0 C# and VB Evolution
Dynamic +
Language Parity
C# 3.0 + VB 9.0
Language Integrated
Query
C# 2.0 + VB 8.0
Generics
C# 1.0 + VB 7.0
Managed Code

9. A bit of evolution
•
•
•
•
Synchronous programming
APM – Asynchronous Programming Model
EAP – Event Asynchronous Pattern
Async (TAP) – Task Asynchronous Pattern

10. Synchronous…

11. Asynchronous with EAP

12. Asynchronous with Async /
TAP

13. Look mom, no Callbacks!!

14. Basics of Async and Await

15. async
makes your method asynchronous

16. await
makes the rest of your method a
callback

17. Task
lets you coordinate activities

18. Task returning vs void
returning
async Task FooAsync(…);
async void Foo_Click(…);
•
•
•
Can be awaited
“Give back control”
Delegate asynchronous work
•
•
•
Cannot be awaited
“Fire and forget”
Start separate independent flow
•
•
Use for helper methods
Use for library methods
•
•
Use for event handlers
Use to override void methods

19. DEMO
Using Async & Await

20. “A waiter’s job is to wait on a table until the patrons have finished their meal.
If you want to serve two tables concurrently, you must hire two waiters.”

21. Asynchronous Flow

22. Task<T> combinators
Task
cancel);
Delay(int ms, CancellationToken
Task<T>
Run<T>(Func<T> function);
Task<IEnumerable<T>>
WhenAll<T>(IEnumerable<Task<T>> tasks);
Task<Task<T>>
WhenAny<T>(IEnumerable<Task<T>> tasks);

23. DEMO
Awaiting Tasks & synchronizing
them

24. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

25. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

26. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

27. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

28. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

29. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

30. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}

31. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}


32. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}


33. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}



34. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}



35. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}




36. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}





37. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}






38. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}







39. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}








40. Asynchronous Control Flow
async void DoWorkAsync() {
var t1 = ProcessFeedAsync("www.acme.com/rss");
var t2 = ProcessFeedAsync("www.xyznews.com/rss");
await Task.WhenAll(t1, t2);
DisplayMessage("Done");
}
async Task ProcessFeedAsync(string url) {
var text = await DownloadFeedAsync(url);
var doc = ParseFeedIntoDoc(text);
await SaveDocAsync(doc);
ProcessLog.WriteEntry(url);
}








41. What have we seen?
•
•
•
•
•
Importance of Asynchronous
Async/Await basics
Tasks
Synchronization
Flow

42. Comparing TAP to its
predecessors
// Task Asynchronous Pattern [TAP], with Cancellation and Progress
Task<TR> GetStringAsync(Params..., [CancellationToken Cancel],
[IProgress<TP> Progress])
// Asynchronous Programming Model [APM]
IAsyncResult BeginGetString(Params..., AsyncCallback Callback, object state);
TR EndGetString(IAsyncResult);
// Event-based Asynchronous Pattern [EAP]
class C
{
public void GetStringAsync(Params...);
public event GetStringCompletedEventHandler GetStringCompleted;
public void CancelAsync();
}
class GetStringCompletedEventArgs
{
public TR Result { get; }
public Exception Error { get; }
}




43. Some facts
• Most of the Async methods will complete
Synchronously. They will use a thread only
when really necessary.
• It’s good to minimize the use of Awaits, using
combinators is good (eg, Task.WhenAll).

44. Jose Luis Latorre
Email: joslat@gmail.com
Twitter: @joslat
Blog: http://xamlguy.com