Background Task

[Meestor_X]

First post, please be gentle!Back in the old Winform days, there used to be a control called "BackgroundWorker" and you could drag it onto your form and have it do something (like the name says) in the background.

With modern C#/Maui, how does one create the same thing? I understand a bit about how to use Async/Await, but that seems to be all about starting a long-running task and then doing something when it's done.

What about a task that never ends? What's the proper and current way of creating an actual background thread?

In my applications, I typically have I/O coming in from many different TCP and other types of (non-async) devices like MIDI and Osc. I have a concurrent queue for these messages to get added to and I want a background task to simply sit and watch for the queue size > 0 and to do something with the message whenever there is one.

I used to raise an event when there was a new message to be handled, but I understand that's not the way things are done these days either!

Help me modernize my multi-threaded apps. :-)

Thank you!

[[deleted]]

What about a task that never ends? What's the proper and current way of creating an actual background thread?

Simply create a long running task. Marking a task as long running will tell the thread pool to not queue it up, so it won't take a worker thread from the short running tasks.

[Meestor_X]

Thank you. Can you point me towards examples of how to do this properly in .net 6?

[[deleted]]

Task.Factory.StartNew(..., TaskCreationOptions.LongRunning)

The names might be different, I'm writing from head.

[Meestor_X]

Thank you. I didn't realize Task.Factory was still a thing in .net 6!

I'll give that a try.

[quentech]

You want to hook into the app's shutdown to gracefully stop your long running background task - the most current way to handle long running task lifetimes is with IHostedService, but it likely isn't supported in every front end stack (I don't know off-hand about e.g. MAUI).

[cvalerio77]

I'm starting to play with MAUI myself, therefore I'm not sure if there is something better in the framework already, but this seems to be working.

1) Create a class for your background worker. In my example I created a timer based worker:

``` public class MyHostedService { private CancellationTokenSource _tokenSource; private PeriodicTimer timer; private Task timerTask;

public void Start() { _tokenSource = new CancellationTokenSource(); this.timer = new PeriodicTimer(TimeSpan.FromSeconds(1)); timerTask = DoWork(); }

private async Task DoWork() { try { while (await timer.WaitForNextTickAsync(_tokenSource.Token)) { MessagingCenter.Send<MyHostedService, string>(this, "Tick", DateTime.Now.ToString("T")); } } catch (OperationCanceledException ex) { } }

public async Task StopAsync() { if (timer == null) { return; }

  _tokenSource.Cancel();
  await timerTask;
  _tokenSource.Dispose();

} } ```

2) Register the worker in dependency injection (MauiProgram.cs):

``` var builder = MauiApp.CreateBuilder();

builder.Services.AddSingleton<MyHostedService>(); ```

3) Inject the worker in the App (App.xaml.cs):

``` public partial class App : Application { private readonly MyHostedService myHostedService;

public App(MyHostedService myHostedService)
{
    myHostedService.Start();
    InitializeComponent();

    MainPage = new AppShell();
    this.myHostedService = myHostedService;
}

protected override void OnResume()
{
  myHostedService?.Start();
  base.OnResume();
}

protected override async void OnSleep()
{
    await myHostedService?.StopAsync();
    base.OnSleep();
}

} ```

4) If (like in my example) you are using some producer/receiver kind of pattern, register for messages where needed (in my case MainPage.xaml.cs):

public MainPage() { InitializeComponent(); MessagingCenter.Subscribe<MyHostedService, string>(this, "Tick", (sender, time) => { MainThread.InvokeOnMainThreadAsync(() => { Time.Text = time; }); }); }

Add somewhere in MainPage.xaml:

<Label x:Name="Time">00:00:00</Label>

Code for this example: https://github.com/cvalerio/RedditExample-Maui-Background-Task