cancelling timeout CancellationToken in Ask in order to prevent memory leaks -- a reference to 'result' variable is stored in CancellationToken's callback which prevents it from garbage collection. it's a huge problem when your timeout value is more or less big and your actor returns big data:

 public sealed class LeakActor : ReceiveActor
 {
     public LeakActor()
     {
         Receive<GetDataMessage>(message => Sender.Tell(new byte[10000]));
     }

    public sealed class GetDataMessage { }
}

then call it somewhere:

for (var index = 0; index < 10000; index += 1)
{
    await greeter.Ask<byte[]>(new LeakActor.GetDataMessage(), TimeSpan.FromSeconds(10));
}

the next calls were rearranged because a future actor should set result before _unregister() cancels Token:

_result.TrySetResult(message);
_unregister();