AK1003 - Warning

You should not have a synchronous code inside lambda function when using ReceiveAsync<T>() or ReceiveAnyAsync().

Cause

Using ReceiveAsync<T>() or ReceiveAnyAsync() with synchronous code inside their lambda function is less performant compared to Receive<T>() or ReceiveAny() because they generates an extra ActorTask message plus an additional suspend + resume of the actor's mailbox. That overhead is fine if you're await-ing something, but if the code is essentially synchronous then you should not do so.

An example:

using Akka.Actor;
using System.Threading.Tasks;
using System;

public sealed class MyActor : ReceiveActor
{
    public MyActor()
    {
        // Notice that there are no `await` inside the lambda function,
        // The lambda function is essentially synchronous
        ReceiveAsync<string>(async str => {
            Sender.Tell(str);
        }):
    }
}

Resolution

Use Receive<T>() or ReceiveAny() instead.

Here's an example on how to fix the above example:

using Akka.Actor;
using System.Threading.Tasks;
using System;

public sealed class MyActor : ReceiveActor
{
    public MyActor()
    {
        // Notice we have replaced `ReceiveAsync` with `Receive`
        // and removed the async keyword
        Receive<string>(str => {
            Sender.Tell(str);
        }):
    }
}