1. DEV422 Becoming a C# Time Lord Joe Albahari 2/5/2019 11:46 AM
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. “ ” “ ” “ ” Humans can’t reliably write free-threaded code
- Chris Brumme, Microsoft ” “
If you don’t believe writing multithreaded code is hard, do everyone a favor and don’t write any ” “
Writing multithreaded code is like juggling chainsaws ”

3. Race conditions Deadlocks Heisenbugs Wrong granularity Tearing
Forgotten synchronization
Priority inversion
Heisenbugs
Cascading failure
Wrong granularity
Weeping Angels
Race conditions
Silent failure
Tearing
Deadlocks
Lock convoys
Shared writable state…

4. Programming concurrency is easy!(ish)
Even with shared writable state!

5. The problem is one of separation

7. Structured Parallelism makes it easy to isolate concurrency

8. What about unstructured concurrency?
Data is spread out over time rather than space.
Work may be compute-bound or I/O-bound. Or both.

9. Can we separate concurrency in unstructured scenarios?
Yes!
Requires language support
Requires a mind-shift

10. What is Space Programming?
Assume data is already there, spread out over space
Think in terms of execution
Pull data as needed, ignoring latency

11. Why is ignoring latency bad?
Causes long-running methods
Why are long-running methods bad?
Forces caller to initiate thread-based concurrency for responsiveness.
Shared writable state then leaks!

12. First Law of Time: No toxic long-running methods
Toxic = accessing shared writable state
Long-running means >50ms
This means no blocking
Instead, program asynchronously

13. What is Asynchronous Programming?
Deals with latency without blocking
An async method returns quickly to the caller
The method starts the operation.
When complete, it runs a callback (continuation)

14. An adult in the temporal world
An asynchronous method takes responsibility for its latency
An adult in the temporal world

15. How do adults behave? They take responsibility for latency
They deal properly with failure
They cooperate with other adults (composition)

16. Dealing with Failure
Silent sulking
Tantrum

17. Composition

18. void GetWebPageAsync ( string uri, Action<string> continuation){
... }
GetWebPageAsync(“...”, Console.WriteLine);

19. Task<string> GetWebPageAsync (string uri){
... }

20. Task<TResult> is a Future
ContinueWith() method
Result property
A future is an asynchronous adult!

21. Time vs. concurrency The two are related
When we’re doing concurrency, we’re doing time
But we can do time without concurrency? Yes!
Time is easier than concurrency.

22. Space
Concurrency

23. Space

24. Space
(Hard) concurrency
Time

25. Demo Time without concurrency 2/5/2019 11:46 AM
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

27. Second Law of Time: Isolate Concurrency
Isolate concurrency from both space and time
Favour time over concurrency

28. Third Law of Time: Use the Tardis await jumps forward in time
Program the future as though it were present
Preserve pull-based logic & fault handling
The Tardis avoids blocking

29. Demo Composition 2/5/2019 11:46 AM
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

30. Fourth Law of Time: Compose
Apply composition patterns to time and concurrency objects
Use combinators / operators

31. Four Laws Of Time No toxic long-running methods
Separate space, time & concurrency
Use the tardis (await)
Compose space & time objects

32. Latency is one kind of time problem
What about asynchronous sequences?
Naturally lend themselves to push-based approaches

33. What do Timelords think of events?

35. 2/5/ :46 AM
Demo
Heartbeat
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

36. PULL PUSH interface IEnumerable<out T> {
IEnumerator<T> GetEnumerator(); }
interface IEnumerator<out T> :
IDisposable
bool MoveNext();
T Current { get; }
PUSH
interface IObservable<out T> {
IDisposable Subscribe (IObserver<T>); }
interface IObserver<in T>
void OnNext (T value);
void OnCompleted();
void OnError (Exception error);

37. Summary Isolation is key to simplifying concurrency
For unstructured concurrency, use futures and observables
Futures and observables lessen and isolate concurrency
Follow the Four Laws of Time

38. Give time the same respect as space.

39. Related content Find Me Later At DevDen in Expo Hall 1pm today
2/5/ :46 AM
Related content
Find Me Later At DevDen in Expo Hall 1pm today
Download LINQPad for sample code
Get the book!
C# 5.0 in a Nutshell – Amazon or O’Reilly
Reactive extensions: rx.codeplex.com
Browse/ask questions on StackOverflow
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

40. Resources Learning TechNet Developer Network
2/5/ :46 AM
Resources
Learning
Sessions on Demand
Virtual Academy
TechNet
Developer Network
Resources for IT Professionals
Resources for Developers
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

41. 2/5/ :46 AM
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.
© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows, and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.