This document discusses new features in C# 5.0, with a focus on asynchronous programming using async and await. It begins with an overview of the evolution of C# from versions 1.0 to 5.0. It then demonstrates how to update a synchronous UI application to an asynchronous one using async and await. It shows how async avoids deadlocks and supports cancellation. Examples are provided for asynchronous console and unit test applications. The document also discusses new attributes for source code caller identification and breaking changes in C# 5.0. Resources for further reading are provided.

1. What’s New In C# 5.0
Paulo Morgado

2. Paulo Morgado
CodePlex
Revista
PROGRAMAR

3. A Language For Each Generation

4. The Evolution Of C#
C# 1.0 C# 2.0 C# 3.0 C# 4.0 C# 5.0
Managed Generics LINQ Dynamic Async

5. The Evolution Of C#
C# 1.0 C# 2.0 C# 3.0 C# 4.0 C# 5.0
Managed Generics LINQ Dynamic Async
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clicking won’t make it come any faster

6. Demo
Synchronous UI Application

7. Synchronous UI Application
private void
HandleLoadButtonClick(object
sender, EventArgs e)
{
try
{
this.loadButton.Visible =
false;
this.progressBar.Visible =
true;
this.pictureBox.Image =
null;
var image =
this.LoadImage();
this.pictureBox.Image =
image;
}
catch (Exception ex)
{
// ...
}
finally
{
this.loadButton.Visible =
true;
this.progressBar.Visible =
false;
}
}
private Image LoadImage()
{
var imageBytes = new
WebClient().DownloadData(Settings.
Default.ImageUrl);
var image =
Bitmap.FromStream(new
MemoryStream(imageBytes));
return image;
}

8. Introducing Async - Yesterday
Click
void LoadImage()
{
// ...
LoadLocalData(...);
// ...
}
void Button_Click(...)
{
LoadImage();
UpdateView();
}
Click
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9. Introducing Async - Today
Click
void LoadImage()
{
// ...
DownloadRemoteData(...);
// ...
}
void Button_Click(...)
{
LoadImage();
UpdateView();
}
Click
Messagepump

10. Demo
Add the async & await keywords

11. Add the async & await keywords
private async void
HandleLoadButtonClick(object sender,
EventArgs e)
{
try
{
this.loadButton.Visible = false;
this.progressBar.Visible = true;
this.pictureBox.Image = null;
var image = await
this.LoadImageAsync();
this.pictureBox.Image = image;
}
catch (Exception ex)
{
// ...
}
finally
{
this.loadButton.Visible = true;
this.progressBar.Visible = false;
}
}
private async Task<Image> LoadImageAsync()
{
var imageBytes = await new WebClient()
.DownloadDataTaskAsync(Settings.Default.Image
Url);
var image = Bitmap.FromStream(new
MemoryStream(imageBytes));
return image;
}

12. Introducing Async
async void Button_Click(...)
{
await LoadImageAsync();
UpdateView();
}
async Task LoadImageAsync()
{
// ...
await DownloadRemoteDataAsync(...);
// ...
}
Messagepump
void LoadImage()
{
// ...
DownloadRemoteData(...);
// ...
}
void Button_Click(...)
{
LoadImage();
UpdateView();
}
Click

13. Introducing Async
Click
async Task LoadImageAsync()
{
// ...
await DownloadRemoteDataAsync(...);
// ...
}
async void Button_Click(...)
{
await LoadImageAsync();
UpdateView();
}
Click
Messagepump
Task ...
DownloadRemoteDataAsync
Task ...
LoadImageAsync
Download
LoadImage

14. Demo
Async UI app: re-entrancy and deadlock

15. Async UI app: deadlock
private void
HandleLoadButtonClick(object sender,
EventArgs e)
{
try
{
this.loadButton.Visible =
false;
this.progressBar.Visible =
true;
this.pictureBox.Image = null;
var image =
this.LoadImageAsync()
.Result;
this.pictureBox.Image = image;
}
catch (Exception ex)
{
// ...
}
finally
{
this.loadButton.Visible = true;
this.progressBar.Visible =
false;
}
}
private async Task<Image>
LoadImageAsync()
{
var imageBytes = await new
WebClient()
.DownloadDataTaskAsync(Settings.Default
.ImageUrl);
var image = Bitmap.FromStream(new
MemoryStream(imageBytes));
return image;
}

16. Demo
Async with cancelation

17. Async with cancelation
private async void HandleLoadButtonClick(object
sender, EventArgs e)
{
try
{
this.loadButton.Visible = false;
this.progressBar.Visible = true;
this.cancelButton.Visible = true;
this.pictureBox.Image = null;
var a = SynchronizationContext.Current;
var image = await this.LoadImageAsync();
var b = SynchronizationContext.Current;
this.pictureBox.Image = image;
}
catch (Exception ex)
{
// ...
}
finally
{
this.loadButton.Visible = true;
this.progressBar.Visible = false;
this.cancelButton.Visible = false;
}
}
private async Task<Image> LoadImageAsync()
{
Image image = null;
var a = SynchronizationContext.Current;
try
{
this.cancelationTokenSource = new
CancellationTokenSource();
var imageResponse = await new
HttpClient()
.GetAsync(Settings.Default.ImageUrl,
cancelationTokenSource.Token)
.ConfigureAwait(false);
var x = SynchronizationContext.Current;
if (imageResponse != null)
{
var imageStream = await
imageResponse.Content
.ReadAsStreamAsync();
var c =
SynchronizationContext.Current;
image =
Bitmap.FromStream(imageStream);
}
}
catch (TaskCanceledException ex)
{
}
var b = SynchronizationContext.Current;
return image;
}
private CancellationTokenSource
cancelationTokenSource;
private void HandleCancelButtonClick(object
sender, EventArgs e)
{
if (this.cancelationTokenSource != null)
{
this.cancelationTokenSource.Cancel();
this.cancelationTokenSource.Dispose();
this.cancelationTokenSource = null;
}
}

18. Demo
Async console app

19. Async console app
class Program
{
static void Main(string[] args)
{
Run().Wait();
}
static async Task Run()
{
await Task.Yield();
}
}

20. Demo
Async unit tests

21. Async unit tests
[TestMethod]
public async Task TestMethod1()
{
await Task.Delay(5000);
Assert.Fail();
}

22. Source Code Caller ID

23. Source Code Caller ID
• CallerFilePathAttribute
– Allows you to obtain the full path of the source file that contains the caller.
This is the file path at the time of compile.
• http://msdn.microsoft.com/library/system.runtime.compilerservices.callerfilepathattribute.aspx
• CallerLineNumberAttribute
– Allows you to obtain the line number in the source file at which the
method is called.
• http://msdn.microsoft.com/library/system.runtime.compilerservices.callerlinenumberattribute.aspx
• CallerMemberNameAttribute
– Allows you to obtain the method or property name of the caller to the
method.
• http://msdn.microsoft.com/library/system.runtime.compilerservices.callermembernameattribute.aspx

24. Source Code Caller ID - Examples
static void TraceMessage(
string message,
[CallerMemberName] string memberName = "",
[CallerFilePath] string sourceFilePath = "",
[CallerLineNumber] int sourceLineNumber = 0)
{
Trace.WriteLine(
string.Format(
"{0} at {1} in {2}:line {3}",
message,
memberName,
sourceFilePath,
sourceLineNumber));
}

25. Source Code Caller ID - Examples
private string field;
public string Property
{
get { return this.field; }
set
{
if (this.field != value)
{
this.field = value;
this.NotifyPropertyChanged();
}
}
}
protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
// …
}

26. Breaking Changes

27. Breaking Changes
• You can use the iteration variable of a foreach statement in a lambda
expression that’s contained in the body of the loop.
• You can use the iteration variable of a foreach statement in a LINQ
expression that’s contained in the body of the loop.
• Overload resolution has been improved for calls that use named
arguments to access methods that contain params parameters.
• Overload resolution is improved for calls where the algorithm must
choose between a Func<object> parameter and a Func parameter that
has a different type parameter (e.g., string or int?) for a
Func<dynamic> argument.
• Side effects from named and positional arguments in a method call
now occur from left to right in the argument list.
http://msdn.microsoft.com/library/hh678682(v=vs.110).aspx

28. Resources

29. Resources
• C# Reference
– http://msdn.microsoft.com/library/618ayhy6.aspx
• Breaking Changes in C# 5.0
– http://msdn.microsoft.com/library/hh678682(v=vs.110).aspx
• .NET Framework 4.5
– http://msdn.microsoft.com/library/vstudio/w0x726c2(v=vs.110).aspx
• Task Parallel Library (TPL)
– http://msdn.microsoft.com/library/vstudio/dd460717.aspx
• Asynchronous Programming with Async and Await (C# and Visual
Basic)
– http://msdn.microsoft.com/library/hh191443.aspx

30. Resources
• Task-based Asynchronous Pattern
– http://msdn.microsoft.com/library/hh191443.aspx
• Task.Run vs Task.Factory.StartNew
– http://blogs.msdn.com/b/pfxteam/archive/2011/10/24/10229468.aspx
• An Async Premier
– http://msdn.microsoft.com/vstudio/jj573641.aspx
• Eduasync by Jon Skeet
– http://msmvps.com/blogs/jon_skeet/archive/tags/Eduasync/default.aspx
• Eric Lippert's Blog
– http://ericlippert.com/
– http://blogs.msdn.com/b/ericlippert/archive/tags/c_2300_+5-0/async/

31. Resources
• Lucian Wischik's Blog
– http://blogs.msdn.com/b/lucian/archive/tags/async/
• Parallel Programming Team Blog
– http://blogs.msdn.com/b/pfxteam/archive/tags/async/
• What’s new in C#5? – Red Gate
– http://www.youtube.com/watch?v=z7nry67oeKc
• Novidades Do C# 5.0 – Comunidade NetPonto
– http://www.youtube.com/watch?v=7Tl6CHf86z4
• Sample Code
– http://code.msdn.microsoft.com/C-50-AsyncAwait-Demo-Code-334679a5

32. Resources
• Paulo Morgado
– @PauloMorgado
– http://PauloMorgado.NET/
– http://mvp.support.microsoft.com/profile/Paulo.Morgado
– http://msmvps.com/blogs/paulomorgado/
– http://weblogs.asp.net/paulomorgado/
– http://pontonetpt.org/blogs/paulomorgado/
– http://www.codeproject.com/Members/PauloMorgado
– http://code.msdn.microsoft.com/site/search?f%5B0%5D.Type=User&f%5B
0%5D.Value=Paulo%20Morgado
– http://www.codeplex.com/UserAccount/UserProfile.aspx?UserName=Paul
oMorgado
– http://www.slideshare.net/PauloJorgeMorgado

33. Q & A

34. Thank You!