1. a tour of
Asynchronous Programming
[Async CTP 3]

2. srikanth@brainscale.com/vishwanath.srikanth@gmail.com
Vishwanath.srikanth
Vishsrikanth
Vishwanathsrikanth.wordpress.com
Vishwanath Srikanth

3. Topics for this Presentation
Earlier ways Awaiting Task Task based
of Async asynchronously Programming
We have features for every step of the way

4. EARLIER WAYS OF PROGRAMMING
ASYNC

5. Async Programming
Why do we need async?
• Responsive UI.
• Leverage Computing Power.
• Better Utilization of Resources.
• Better user experience.
What is expected from Async programming patterns?
• Transparent Remote operations
• Easy to code
• Cancellations, Timeouts, Preserving threads during blocking awaits etc.

6. Pre matured ways of async programming.
Recommended Async Programming Concepts
• Don’t wait for the response.
• Return immediately after issuing a async request
• Let the response call you back.
Earlier ways
• IAsyncResult Pattern Ex: BeginRead, EndRead
• Event based Asynchronous pattern
Sync
Async

7. Pre matured ways of async programming.
What went wrong?
• Disruptive Program Structure
• Error prone
• Heavy weight
• Difficult to design and write

8. New way of Async Programming DEMO

9. Awaiting a AWAITING TASK ASYNCHRONOUSLY
Task

10. What is Async CTP?
• A new language feature
• New framework pattern
What do you need to start working on
Async CTP
• Visual Studio 2011 Beta
• Visual Studio 2010 SP1 with Async
CTP
Download from:
http://www.microsoft.com/download/e
n/details.aspx?id=9983

11. Task and Task<T>
• A Task is a representation of ongoing work
• Available in .NET 4
• Task returns nothing, Task<T> returns a result of type T.
• Normal tasks - Independent of Thread.
• Async tasks run on same thread.
• Propagate Exceptions

12. ‘async’ modifier
• Indicates Asynchrony
• Can be used for methods or Events or Methods or Lambdas
• Out and ref are not allowed.
• Analogous to ‘yield’

13. ‘await’ keyword
• Await - Prepend to a method which can return Task, Task<T>
• Everything that continues is compiled asynchronously
• ‘Async’ Runs synchronously until first ‘await’.

14. Task based
Programming TASK BASED ASYNC PATTERN

15. Task based async pattern
Async UI Thread
Caller
Method
Task/Task<T>
Create Task &
Check for callback
Wait for ‘await’
Load the Context
Capture Context continue
Sign up a call back.

16. Task Based Asynchronous Pattern (TAP)
• Task Behavior – Initialization, Exceptions, Target Environment, TaskStatus
• Task States
• Created, WaitingForActivation, WaitingToRun, Running,
WaitingForChildrenToComplete, RanToCompletion, Canceled, Faulted.
• Cancellation
• Cancellations
• Progress Reporting
• Testable
• TaskID
• Task Creation Options – None, Prefairness, LongRunning, AttachedToParent

17. Consuming the Task Based Asynchronous Pattern
• Continue Await using continuewith
• Task.Yield()
• Cancel Context - ConfigureAwait
• Cancellation
• Cancellation.None
• Progress Reporting

18. Building Task-Based Combinators
Task.Run
Task.WhenAll
- Aggregate Exception or All Exceptions

19. Building Task-Based Combinators
Task.FromResult
Task.WhenAny
• Redundancy
• Interleaving
• Throttling
• Early bailout

20. Questions
Thank you!

21. There is more….
Goodies……
• Which namespace does Task belongs to ?
• Can we utilize the power of multicore using
Tasks?