"This actor library runs tasks with the help of fixed number of threads".
This is a M:N user-space scheduler for threads, a re-implementation of what Go provides as part of the language but with 10x the complexity (things that Go doesn't expose: Scheduler, a Task, a SchedulingRule, a Sink, a Filter, a YSPlit and what not).
I'm not a CS historian but this is what Alan Kay complains about when he talks about the pop culture of computer science.
Actor model (https://en.wikipedia.org/wiki/Actor_model) is a somewhat deep idea about structuring systems as independent entities that communicate via sending messages.
A thread is not that. The similarity is superficial.
To the extent that it's about threads that can communicate over channels, it's closer to CSP (https://en.wikipedia.org/wiki/Communicating_sequential_proce...) but as the page says "the two models (CSP and actors) make some fundamentally different choices with regard to the primitives they provide".
It's telling that the only time an actual actor is mentioned is in the name of the library. The actual code talks about tasks, channels, schedulers.
1) Create other actors at runtime
2) Send and receive messages to/from other actors asynchronously
3) Can do something in response to messages and then optionally change this behavior in anticipation of the next message.
(Meaning: if you have to predefine all "actors" at compile time, this is not actor model. If you have to predefine "exchange points" AKA channels to communicate between two actors synchronously, this is not actor model. If you can't change your behavior at runtime, this is not actor model.)
Actors are very dynamic entities operating in a wild west environment without any guarantees (about delivery, or message ordering, etc -- just like the IP stack). Messages are sent in "fire and forget" fashion. The power of actor model is that it can be useful even in such an environment.
Thank you for the feedback. This helps me a lot in deciding which area of this library needs more explanations. In a followup post I'll show 1) how to create actors run-time, 2) send and receive messages 3) respond to messages. 4) that the messages are async
I don't really think that too many people are aware of Hewitt et al's intentions behind the Actor model - e.g. no global knowledge (emulating a scientific community), actors can only send messages to known acquaintances, only async messages, no need for additional baggage per actor such as mailboxes or lightweight threads. I'm not sure that matters here though.
The author is clearly interested in developing a derivative of Erlang/OTP that works for the author. Erlang is often described as an implementation of the actor model.
I respect the Erlang/OTP model a lot. This library is inspired by that. I don't have the illusion to get anywhere close to it in a reasonable amount of time.
There are also differences to the Erlang/OTP too. This library uses typed messages and taking advantage of the compiler to do type checking. I found it is easier to create this library if 1) the number of input and output channels are fixed 2) the topology of who sends to whom is fixed when the tasks are passed to the scheduler.
The author here. Thank you for the feedback. I take it as my failure explaining what this library is about. I will write a followup post to explain why I think this library supports an actor-like programming model.
This looks awesome. It's exactly the sort of thing I've been looking for as a means to bridge the gap between web libraries that want to own the mio::poll::poll() loop (providing no access to register listeners of your own) and rolling literally everything myself. It's a BIG gap!
I was just about to start writing the equivalent of rotor as a thin plugin you can tack on to a mio event loop alongside whatever but with this I think I can get away with simply starting an event loop ahead of time and passing events back into my web app. It'll be interesting to play with it.
I just started diving more into Rust recently and have been trying to understand the current state of the ecosystem. I've been looking at a bunch of the libraries that expand upon mio, but this is the first time I've heard of `rotor`. Besides searching crates.io and judging based on the download numbers, is there better way to discover important crates?
> I've been looking at a bunch of the libraries that expand upon mio, but this is the first time I've heard of `rotor`.
The current state of affairs is somewhat up in the air because Alex Crichton (futures) and Carl Lerche (mio) are working on the Tokio project [0][1], which is likely to become the most favored way to do things on top of mio.
I just want to add that I really like where Tokio is going. The architecture seems well-thought-out and exactly the sort of thing I'm looking for. There's only one problem though...
It's still under construction!
Every day something new breaks, haha. Whether it's tokio-middleware with the "what was I thinking?" patch:
The good news though is that it is obviously being worked on--heavily. The Rust ecosystem is so new that it feels a bit like we're in the Wild West. Someone comes up with a decent way to do something and then after a bit of ecosystem evolution we're back to the drawing board since, "there's a better way."
This is all very good because it means that the Rust ecosystem is evolving rapidly. It also means that developers are productive enough in the language that entire frameworks can be re-written from scratch in a reasonably short amount of time. I think it's a good demonstration of how effective the language is overall at its goal of improving productivity (as far as systems programming languages go).
> The Rust ecosystem is so new that it feels a bit like we're in the Wild West.
This is pretty normal for an ecosystem at Rust's stage of development. Ecosystem development is always something of a monkeys-on-typewriters effect and if you continuously have major disruptions in the language, you wind up with Javascript Fatigue.
What I'm particularly impressed with in Rust is the core team's leadership. I'm looking forward to Tokio because I think it's likely to have Rails-like dominance over the ecosystem. This is exciting because it gets us monkeys all pointed in the same direction instead of writing another postgresql client because existing ones don't support the current flavor of event loop that I'm using. Getting to the point where we can snap a bunch of pieces together and have a network service is huge for office advocacy. I think it was a key factor in Ruby's wins over the more established Python web community when observing from the Python side.
I'm also pleased that the Rust core team is focused on my pet areas of improvement: editor support, impl Trait, and async network services.
I'm one of the persons waiting for a stable tokio so badly. I have many use cases for this in my Rust projects that are either currently doing async io so-so or doing stuff like firing http requests in sync using the tools available. The situation in hyper land is not very cool at the moment, master being async but requiring you to write the callbacks, stable using too old openssl and the tokio branch not compiling.
With tokio I could unify my code base and make the code simpler and easier to follow.
There are also some "Are we X yet?" sites that cover ecosystem maturity for specific topics. Here are all the Rust-specific sites linked from Mozilla's page (https://wiki.mozilla.org/Areweyet):
"This actor library runs tasks with the help of fixed number of threads".
This is a M:N user-space scheduler for threads, a re-implementation of what Go provides as part of the language but with 10x the complexity (things that Go doesn't expose: Scheduler, a Task, a SchedulingRule, a Sink, a Filter, a YSPlit and what not).
I'm not a CS historian but this is what Alan Kay complains about when he talks about the pop culture of computer science.
Actor model (https://en.wikipedia.org/wiki/Actor_model) is a somewhat deep idea about structuring systems as independent entities that communicate via sending messages.
A thread is not that. The similarity is superficial.
To the extent that it's about threads that can communicate over channels, it's closer to CSP (https://en.wikipedia.org/wiki/Communicating_sequential_proce...) but as the page says "the two models (CSP and actors) make some fundamentally different choices with regard to the primitives they provide".
It's telling that the only time an actual actor is mentioned is in the name of the library. The actual code talks about tasks, channels, schedulers.