C# Use async/await on UdpClient Receive

Question

The following code uses Task to receive asyncronously and shows the received result in the console:

private void ReceiveMessage()
{
    Task.Run(async() => 
    {
         using(var udpClient = new UdpClient(15000))
         {
             while(true)
             {
                 var receivedResult = await udpClient.ReceiveAsync();
                 Console.Write(Encoding.ASCII.GetString(receivedResult.Buffer));
             }
         }
    });
}

I want to learn how to use async/await functions so I would like to know how to make the function ReceiveMessage() asynchronously by using async/await?

I think you might to want to give [this](https://msdn.microsoft.com/en-us/library/mt674882.aspx) a read.. — , Jan 02 '17 at 14:29

René Vogt · Accepted Answer · 2017-01-02T14:41:00.003

6

If you want the whole method to be awaitable, simply change it to that:

private async Task ReceiveMessage()
{
     using(var udpClient = new UdpClient(15000))
     {
         while(true)
         {
             var receivedResult = await udpClient.ReceiveAsync();
             Console.Write(Encoding.ASCII.GetString(receivedResult.Buffer));
         }
     }
}

You don't need Task.Run() anymore, which would use a thread. That thread is not needed. The method now returns to the caller while awaiting ReceiveAsync().
When ReceiveAsync() finishes, the method is (eventually) resumed at Console.WriteLine().

edited Jan 02 '17 at 14:41

answered Jan 02 '17 at 14:34

René Vogt

43,056
14
77
99

1

Actually this code is correct, but it does not make the method awaitable as you mention. You can't await void, you await Tasks. – Trickzter Jan 02 '17 at 14:39
@Trickzter fair enough, I'll fix that. – René Vogt Jan 02 '17 at 14:40

Trickzter · Answer 2 · 2017-01-02T14:41:25.843

0

Simply add another async/await to your function:

private async void receiveMessage()
{
    await Task.Run(async() => 
    {
         using(var udpClient = new UdpClient(15000))
         {
             while(true)
             {
                 var receivedResult = await udpClient.ReceiveAsync();
                 Console.Write(Encoding.ASCII.GetString(receivedResult.Buffer));
             }
         }
    });
}

If you want to write a method being awaitable, return a task:

private Task foo(){
    Task doStuff = new Task(() => {});
    doStuff.Start();
    return doStuff;
};

//Another method
private async void bar()
{
    await foo();
}

Update: As mentioned below, you do really not need the execution of that task on a thread inside the thread pool. It's not wrong, but useless. For better usage, you can use:

private async void receiveMessage()
{
     using(var udpClient = new UdpClient(15000))
     {
         while(true)
         {
             var receivedResult = await udpClient.ReceiveAsync();
             Console.Write(Encoding.ASCII.GetString(receivedResult.Buffer));
         }
     }
}

edited Jan 02 '17 at 14:41

answered Jan 02 '17 at 14:29

Trickzter

471
3
14

3

The `Task.Run()` is unnecessarily using a thread from the thread pool. Since `ReceiveAsync()` is already `await`ed, this is a waste of resources. – René Vogt Jan 02 '17 at 14:35
That's totally correct, but not point of discussion here. He was only asking for a way to make it working asynchronously and I just completed the code. But you are right sir. – Trickzter Jan 02 '17 at 14:38
2

The purpose of SO is to give helpful answers that can help future readers, too. Of course you answered OP's immediate question, but even he states that he _wants to learn_. Showing bad code as a good example has a little smell. – René Vogt Jan 02 '17 at 14:40
@RenéVogt agreed. – Trickzter Jan 02 '17 at 14:44

score 0 · Answer 3 · answered Jan 02 '17 at 14:36

The code you have is valid if you want it to be fire and forget, listening on a separate thread. If you not want this, I would remove the Task.Run and be sure to return a Task in your method, like this:

private async Task ReceiveMessage()
{
    using (var udpClient = new UdpClient(15000))
    {
        while (true)
        {
            var receivedResult = await udpClient.ReceiveAsync();
            Console.Write(Encoding.ASCII.GetString(receivedResult.Buffer));
        }
    }
}

C# Use async/await on UdpClient Receive

3 Answers3

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