BDotnet Session on C# 5

1. C# 5: Deep Drive into
Asynchronous Programming
By- Praveen Kumar Prajapati
Blog: praveenprajapati.wordpress.com

2. Agenda
 What’s asynchrony
 Related Terms and Need of Asynchrony
 Why TPL: The Free Lunch is Over
 C# 4: Task Parallel Library
 C# 4: TPL Demo
 C# 5 : Asynchronous Programming
 C# 5 : Behind the Scene
 C# 5 : Async Demo
 Summery

3. What’s asynchrony
 What’s asynchrony?
 Greek origin
 a (not)
 syn (together with)
 chronos (time)
 Multiple parties evolving in time independently
 Not being blocked
 Synchronous  Wait for result before returning
 string DownloadString(...);
 Asynchronous  Return now, call back with result
 void DownloadStringAsync(..., Action<string> callback);

4. Related Concepts
 Multithreading
 Use of multiple threads
 Concurrency
 Order in which multiple tasks execute is not determined
 Parallelism
 True simultaneous execution (e.g. multicore)

5. Need of Asynchrony
 Increasingly connected applications
 More latency
 More UI responsiveness problems
 More scalability issues
 Asynchronous programming
 Becoming the norm in responsive, scalable apps
 More relevant to Metro Style Apps and Window Phone Apps
 Async-only APIs, e.g., JavaScript and Silverlight

6. Asynchronous Programming
Model
Hang
UI Thread
UI
Messages
DisplayPhotos
DownloadDataAsync
ParseResponse

7. Why TPL :
The Free Lunch is Over
 A paradigm shift
 Then: Faster clocks
 Now: More cores => End of the Free Lunch
 The Free Lunch is Over
 By Herb Sutter in Feb/Mar 2005
 The Free Lunch Is Over
-A Fundamental Turn Toward Concurrency in Software
 Why You Don’t Have 10GHz Today

8. The Free Lunch is Over

9. Single to Multiple Core
Transition

10. C# 4 : Task Parallel Library
 “Applications will increasingly need to be concurrent if
they want to fully exploit continuing exponential CPU
throughput gains”
 What would be the optimum number of threads for this
machine?
 But how to decide the degree of concurrency? What if
server gets more core in future – Change in underlying
hardware?

11. C# 4 : Task Parallel Library
 The TPL scales the degree of concurrency dynamically to
most efficiently use all the processors that are available.
 In addition, the TPL handles the partitioning of the work,
the scheduling of threads on the ThreadPool,
cancellation support, state management, and other low-
level details.
 By using TPL, you can maximize the performance of your
code while focusing on the work that your program is
designed to accomplish.

12. Thread vs. Task
 Task: A Task is a future or a promise. (Some people use
those two terms synonymously, some use them differently,
nobody can agree on a precise definition.)
 Basically, a Task<T> "promises" to return you a T, but not
right now .
 Thread: A Thread is one of many ways to fulfill that
promise. But not every Task needs a Thread. If the value
you are waiting for comes from the file system or a
database or the network, then there is no need for a
thread. The Task might just register a callback to receive
the value when the disk is done seeking.
 TPL Demo

13. C# 5 : Asynchronous
Programming
 New Keyword introduces:
 async
 Await
 Asynchronous Methods
 As simple as synchronous code
 Unifies computational, network and I/O asynchrony
 More scalable servers
 More responsive UI

14. C# 5 : Behind the Scene
public async Task<XElement> GetXmlAsync(string url) {
var client = new HttpClient();
var response = await client.GetAsync(url);
var text = response.Content.ReadAsString();
return XElement.Parse(text);
}
public Task<XElement> GetXmlAsync(string url) {
var tcs = new TaskCompletionSource<XElement>();
var client = new HttpClient();
client.GetAsync(url).ContinueWith(task => {
var response = task.Result;
var text = response.Content.ReadAsString();
tcs.SetResult(XElement.Parse(text));
});
return tcs.Task;
}

15. C# 5 : Async Demo
 Demo: Use of async and await
 How it reduces efforts and make code better

16. Some Point to Remember
 For any async block it is important to have at least one
await, otherwise the whole block will work
synchronously.
 Any async method should postfix Async (as a rule), so
your method name should look like MyMethodAsync
which you put an async keyword before it.
 Exceptions to the convention can be made where an
event, base class, or interface contract suggests a
different name.
 Any async method can return void(call and forget), Task
or Task<T> based on the Result the await method
sends.
 Everything is managed by a State Machine Workflow by
the compiler

17. Summery
 Asynchronous Programming and related terms
 Why it is so relevant in current days
 Free Lunch is Over
 TPL and Task
 New Kew words : async and await
 Rules and recommendation for new features

18. References
• Visual Studio Asynchronous Programming
http://msdn.microsoft.com/en-us/vstudio/async.aspx
• Task Parallel Library
http://msdn.microsoft.com/en-us/library/dd460717.aspx
• The Future of C# and VB @PDC10
http://player.microsoftpdc.com/Session/1b127a7d-300e-4385-af8e-ac747fee677a
• Fabulous Adventures in Coding
http://blogs.msdn.com/b/ericlippert
• John Skeet: Coding Blog
http://msmvps.com/blogs/jon_skeet

19. Thanks to You All
Let us grow together
Keep in touch:
Blog: praveenprajapati.wordpress.com