是否建议/可以在新线程中运行异步void方法？

Question

I have an old piece of code (.NET 3.5) where I run in a separate thread the registration of new TcpClient:

Old code:

public class TcpServer
{
    private readonly TcpListener _tcpListener;

    public TcpServer(int port)
    {
        _tcpListener = new TcpListener(IPAddress.Any, port);
    }

    public void StartListening()
    {
        _tcpListener.Start();

        var t = new Thread(new ThreadStart(AcceptConnections));
        t.Start();
    }

    private void AcceptConnections()
    {
        while (true)
        {
            var client = _tcpListener.AcceptTcpClient();

            // Some stuff
        }
    }
}

The goal of this code is to avoid blocking the app while waiting for new clients. I am porting this code to .NET Standard and I wonder whether I have to use the new features of .NET.

I am talking about async/await and Task .

Async Thread version

Since this thread will last as long as the whole application, I first considered to simply replace the actual method by the new asynchronous one. But if I do so, I end up with a new thread running an async void method:

public class TcpServer
{
    private readonly TcpListener _tcpListener;

    public TcpServer(int port)
    {
        _tcpListener = new TcpListener(IPAddress.Any, port);
    }

    public void StartListening()
    {
        _tcpListener.Start();

        var t = new Thread(new ThreadStart(AcceptConnectionsAsync));
        t.Start();
    }

    private async void AcceptConnectionsAsync()
    {
        while (true)
        {
            var client = await _tcpListener.AcceptTcpClientAsync();

            // Some stuff
        }
    }
}

It is not recommended to write async void method except in rare case (like event handler).

Is this case acceptable?

Async task version

As a new option, I run the registration in a Task :

public class TcpServer
{
    private readonly TcpListener _tcpListener;

    public TcpServer(int port)
    {
        _tcpListener = new TcpListener(IPAddress.Any, port);
    }

    public Task StartListeningAsync()
    {
        _tcpListener.Start();

        return Task.Run(async () => await AcceptConnectionsAsync());
    }

    private async Task AcceptConnectionsAsync()
    {
        while (true)
        {
            var client = await _tcpListener.AcceptTcpClientAsync();

            // Some stuff
        }
    }
}

With this code, as long as I do not await the AcceptConnectionsAsync call, the app is not blocked (I simplify the code with a while(true) but I handle the closure of the app and the end of the listening properly, I can call the await there or even fire-and-forget it).

But as I said, this action is supposed to last as long as the whole application, I think a new thread is more appropriate (in term of architecture at least but also in term of efficiency).

Am I wrong?

Do not change anything to this part of the code

This is the last option I see. I intended to update the code with the Async/Await because I read that the async/await improves the performance of the TcpListener.

But is that true?

Important information

Here are some information I think can be relevant. Do not hesite to ask for further details.

• The application running this code is a Console App. I know this can be important regarding to async/await context?
• The AcceptConnections(Async) method runs a new Task for each new connection (these tasks are short-lived and of type fire-and-forget).
• The main thread performs huge calculations. The best solution is the least impacting regarding to the main thread performance.
• There is one other thread that behave like this one (same duration), responsible for listening the data coming from all clients. I intend to apply the same operations as this one.

Answer 1

But as I said, this action is supposed to last as long as the whole application

No, it doesn't. The method will return almost immediately. That's what it means for a method to be asynchronous. It doesn't block the caller while the work is being done.

Creating a new thread just to call an asynchronous method is like hiring someone to come to your house to put a letter in your mailbox for you. It's more work than just doing it yourself, because the actual act of getting the letter to its destination doesn't actually prevent you from doing work outside of a trivial bit of work to just get it started.