Asynchronous Programming in Visual Basic .NET

Advanced Topics

This section delves into advanced concepts and techniques for asynchronous programming in Visual Basic .NET, building upon the foundational understanding of `Async` and `Await` keywords.

Cancellation and Progress Reporting

Managing the lifecycle of asynchronous operations is crucial for responsive applications. This involves gracefully canceling long-running tasks and providing real-time feedback to the user on the operation's progress.

Using CancellationTokenSource and CancellationToken to signal cancellation.
Implementing progress reporting with IProgress<T>.

Example of cancellation:

                
                    Async Function DownloadFileAsync(url As String, cancellationToken As CancellationToken) As Task(Byte())
                    Dim client As New HttpClient()
                    Using response As HttpResponseMessage = Await client.GetAsync(url, cancellationToken)
                        response.EnsureSuccessStatusCode()
                        Dim contentBytes As Byte() = Await response.Content.ReadAsByteArrayAsync()
                        Return contentBytes
                    End Using
                    End Function

                    Sub PerformDownload()
                        Dim cts As New CancellationTokenSource()
                        ' ... trigger cancellation when needed
                        Dim downloadTask As Task(Of Byte()) = DownloadFileAsync("http://example.com/largefile.zip", cts.Token)
                        ' ... handle task completion or cancellation
                    End Sub
                
            

Task Composition and Synchronization Context

Understanding how to compose multiple asynchronous operations and how the synchronization context affects UI updates is vital for robust applications.

Using Task.WhenAll and Task.WhenAny for parallel execution.
The role of the SynchronizationContext in UI thread marshaling.
Avoiding deadlocks when mixing synchronous and asynchronous code.

Advanced Async/Await Patterns

Exploring more sophisticated patterns that leverage the async/await paradigm for cleaner and more efficient code.

Implementing custom awaitable types.
Using ConfigureAwait(False) to improve scalability in library code.
Asynchronous streams (IAsyncEnumerable<T>) for handling sequences of data over time.

                
                    Public Async Function ProcessDataAsync() As Task
                        ' Example of Task.WhenAll
                        Dim task1 As Task = FetchDataPart1Async()
                        Dim task2 As Task = FetchDataPart2Async()
                        Await Task.WhenAll(task1, task2)
                        ' Process combined data
                    End Function
                
            

Best Practices and Pitfalls

Learn about common mistakes and recommended practices to ensure efficient and correct asynchronous programming.

Choosing the right return type: Task, Task(Of T), or ValueTask.
Handling exceptions correctly in asynchronous methods.
The importance of non-blocking I/O operations.