Akka.Streams: when using Context.Materializer, encourage users to cache it into a backing property or field

[Aaronontheweb]

Here's the issue - using an example from Phobos's test suite:

private sealed class LocalActor: UntypedActor
    {
        private readonly int[] _messages = { 1, 2, 3 };
        private readonly IActorRef _remote;
        private readonly ILoggingAdapter _log;

        public LocalActor(IActorRef remote)
        {
            _remote = remote;
            _log = Context.GetLogger();
        }

        protected override void OnReceive(object message)
        {
            if (message is "start-manual")
            {
                _log.Info("Starting stream");

                // test manual span
                using (CreateSpan("StartStream"))
                {
                    Source.From(_messages)
                        .RunWith(
                            Sink.ActorRef<int>(
                                _remote,
                                onCompleteMessage: "complete",
                                onFailureMessage: e => $"fail: {e}"), 
                            Context.Materializer());
                }
            }
            else if (message is "start")
            {
                _log.Info("Starting stream");

                // no manual span
                Source.From(_messages)
                    .RunWith(
                        Sink.ActorRef<int>(
                            _remote,
                            onCompleteMessage: "complete",
                            onFailureMessage: e => $"fail: {e}"), 
                        Context.Materializer());
            }
            else
            {
                Unhandled(message);
            }
        }

Each time we call Context.Materializer() this operation allocates a new group of stream materialization actors - which is not usually what the user intends. So generally, it's a good idea for performance / memory / stability reasons to encourage users to always cache Context.Materalizer() calls.

Important Distinction

Worth nothing: you do not need to cache ActorSystem.Materializer() calls - these are already cached internally as part of akkadotnet/akka.net#6453