AK1001 - Error

Warning

This error has been deprecated because it is not valid, as pointed out in this issue.

Upgrade your Akka.Analyzer version to 0.2.3.1 if this error shows up in your Akka.NET solution.

You should always close over Context.Sender when using PipeTo

Cause

When using PipeTo, you must always close over Sender to ensure that the actor's Sender property is captured at the time you're scheduling the PipeTo, as this value may change asynchronously.

This is a concurrent programming problem: PipeTo will be evaluated and executed at some point in the future because it's an asynchronous continuation, therefore the Context.Sender property, which is mutable and changes each time the original actor processes a message, may change.

An example:

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

public sealed class MyActor : UntypedActor{

    protected override void OnReceive(object message){
        async Task<int> LocalFunction(){
            await Task.Delay(10);
            return message.ToString().Length;
        }

        // potentially unsafe use of Context.Sender
        LocalFunction().PipeTo(Sender); 
    }
}

Resolution

To avoid this entire category of problem, we should close over the Context.Sender property in a local variable.

Here's an example below:

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

public sealed class MyActor : UntypedActor{

    protected override void OnReceive(object message){
        async Task<int> LocalFunction(){
            await Task.Delay(10);
            return message.ToString().Length;
        }

        var sender = Sender;
        LocalFunction().PipeTo(sender); 
    }
}