private int slowFunc(int a,int b)       
 {          
 System.Threading.Thread.Sleep(10000); 
 return a + b;
 }

 private void button1_Click(object sender, EventArgs e)
 {            
 this.button1.Enabled = false; //prevent re-entry 
 var someTask = Task<int>.Factory.StartNew(() => slowFunc(1, 2));
 this.label1.Text = "Result: " + someTask.Result.ToString(); //oops, blocks calling thread 
 this.button1.Enabled = true;       
 }

 private void button1_Click(object sender, EventArgs e)        
 {
 this.button1.Enabled = false;          
 var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); //get UI thread context 
 var someTask = Task<int>.Factory.StartNew(() => slowFunc(1, 2)); //create and start the Task 
 someTask.ContinueWith(x =>     
   {                                          
   this.label1.Text = "Result: " + someTask.Result.ToString();   
   this.button1.Enabled = true;   
   }, uiScheduler  
  );        
 }

 private async void button1_Click(object sender, EventArgs e)
 {
 this.button1.Enabled = false; 
 var someTask = Task<int>.Factory.StartNew(() => slowFunc(1, 2)); 
 await someTask;  
 this.label1.Text = "Result: " + someTask.Result.ToString(); 
 this.button1.Enabled = true;
 }

10 thoughts on “A simple example of async and await in C# 5”

1. It seems like syntactic sugar, not really letting you do anything you couldn’t do already, though admittedly making the code a bit cleaner. I wonder though why they couldn’t just as easily add a second parameter to StartNew() that accepts a closure that is in turn executed immediately after the asynchronous method call completes. Unless I am mistaken, wouldn’t that provide the same functionality?

   So you would get:

   
private async void button1_Click(object sender, EventArgs e)
{
this.button1.Enabled = false;
var someTask = Task.Factory.StartNew(() => slowFunc(1, 2),{
this.label1.Text = "Result: " + someTask.Result.ToString();
this.button1.Enabled = true;
});
}


   1. Lynn

      It is syntactic sugar. Your suggestion would work too, though you would need to allow for the initial task and the continuation to run on different threads. But I prefer await which lets you write the code in a more natural way.

      Tim

2. Sorry. 🙂 I don’t mean to be a grumpy bear. It’s a nice addition. I think what bugs me is that it’s a new keyword in the language and one which affects the execution of a block and which I would be afraid would be easy to miss visually. Meh… it’ll probably be fine. 🙂

3. “Unless I am mistaken, wouldn’t that provide the same functionality?”

   It would require you to write the continuation manually, which is straightforward in this case, but can be tricky if you’re inside loops, try-catch blocks, other continuations, etc. This is comparable to the “yield” keyword.

4. I was hoping the async and await keywords would cut out the explicit use of tasks altogether, im very disappointed to say the least, i was hoping you could do this:

   private async void button1_Click(object sender, EventArgs e)
   {
   this.button1.Enabled = false;
   int liResult = await slowFunc(1, 2);
   this.label1.Text = “Result: ” + liResultResult.ToString();
   this.button1.Enabled = true;
   }

   And have the same outcome, i mean really, surely they could have made it implicitly create the task and start it executing when used with this syntax, whats the point in adding a nice new short keyword for easy access to asynchronous operations if you still have to go and create the task anyway?

   Useless, just useless, i would prefer to just simply use the task directly with the TaskScheduler.FromCurrentSynchronizationContext() method.

5. On another note, i would prefer to implement it in this way, using this pattern you dont have to create a task instance every time you want call the function asynchronously, instead just use the await keyword:

   private Task slowFunc(int a,int b)
   {
   return
   Task.Factory.StartNew(() =>
   {
   System.Threading.Thread.Sleep(10000);
   return a + b;
   });
   }

   private async void button1_Click(object sender, EventArgs e)
   {
   this.button1.Enabled = false;
   this.label1.Text = “Result: ” + (await slowFunc(1, 2)).ToString();
   this.button1.Enabled = true;
   }

   Of course one needs to be careful that the values passed to the function are not disposed (or are immutable as in this case).

6. Can’t wait to see what the VB.NET equivalent looks like. If the way that lambdas are handled by that language are anything to go by, it’ll be syntactically ghastly.

7. Would this be the equivalent, using the Reactive Framework? (Excuse any syntax errors please):

   private void button1_Click(object sender, EventArgs e)
   {
   this.button1.Enabled = false;
   var obs = Observable.Start(slowFunc(1, 2));
   obs.ObserveOn(SynchronizationContext.Current).Subscribe((x) =>
   { this.label1.Text = “Result: ” + x.ToString();
   this.button1.Enabled = true; });

   }

8. Hi
   im working in visual studio 2012 c# , in my program i have method with async keyword..im trying to call normal method from the async method,it working but it doesn’t active another thread ( open the another page or application )
   here is my code ,please help me out

   private async void Button_Click_1(object sender, RoutedEventArgs e)
   {

   string text = await RecognizeTextSearchGrammar();
   if (text != null)
   {
   await Speak(string.Format(“Searching Application {0}”, text));

   result = text;
   match(result); —-> normal method ( trying to open the another application )
   }

   Thanks in advance

9. Hi Lavanya,

   By reviewing your Post, i has noticed that “Your normal method will exeucte only if there is any response from Speak method which called asynchronously.
   By the time you are calling the Speak method, the control suspends this Button1_click and resume once you got the value from Speak Method.

   Regards,
   Arjun.K

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