C# 4 and .NET 4

540 ❘ ChaPTer 20 threAds, tAsks, And synchrOnizAtiOn
{
}
onCompletedDelegate = LongTaskCompletion;
public string LongTask(string input)
{
Console.WriteLine("LongTask started");
Thread.Sleep(5000);
Console.WriteLine("LongTask finished");
return input.ToUpper();
}
public void LongTaskAsync(string input, object taskId)
{
//.
}
private void LongTaskCompletion(object operationState)
{
//.
}
protected void OnLongTaskCompleted(LongTaskCompletedEventArgs e)
{
//.
}
// running in a background thread
private void DoLongTask(string input, AsyncOperation asyncOp)
{
//.
}
}
private void CompletionMethod(string output, Exception ex,
bool cancelled, AsyncOperation asyncOp)
{
//.
}
}
public class LongTaskCompletedEventArgs: AsyncCompletedEventArgs
{
//.
}
code snippet AsyncComponent/AsyncComponent.cs
The method LongTaskAsync needs to start the synchronous operation asynchronously. If the component
allows starting the asynchronous task several times concurrently, the client needs to have an option to map
the different results to the tasks started. This is why the second parameter of LongTaskAsync requires a
taskId that can be used by the client to map the results. Of course, inside the component itself the task ID
needs to be remembered to map the results. .NET provides the class AsyncOperationManager to create
AsyncOperationObjects to help keep track of the state of operations. The class AsyncOperationManager
has one method, CreateOperation(), where a task identifier can be passed, and an AsyncOperation
object is returned. This operation is kept as an item in the dictionary userStateDictionary that was
created earlier.
Then, a delegate of type Action is created, and the method DoLongTask is
assigned to that delegate instance. BeginInvoke() is the method of the delegate used to start the method
DoLongTask() asynchronously, using a thread from the thread pool. The parameters needed with this
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