Tell HN: Lois - Golang like channels for Java

http://flipkart-incubator.github.io/Lois/

by mrphoebs • 12 years ago

24 28 12 years ago

flipkart-incubator.github.io

koevet• 12 years ago

The send/receive paradigm is similar to Actors (Erlang, Akka). What is the main difference between channels and actors?

cronos• 12 years ago

This model is called Communicating sequential processes. Comparison between actor model and CSP can be found here http://en.m.wikipedia.org/wiki/Communicating_sequential_proc...

mrphoebs8• 12 years ago

The bounded nature of channels tie the communicating processes together more intimately. As a result channels are very good for coordination between processes. Both do a good job of communication between concurrent processes/threads.

rakoo• 12 years ago

Channels live at a lower level. Usually when you create a channel you share it between multiple goroutines: It acts exactly like a pipe, and are transparent to what's inside. Moreover, goroutines sending to and receiving from a channel don't know (and don't need to know) what's on the other end.

Actors are more like a combination of a channel and a goroutine: when you send something to the actor, you know what the other end is and you know what it does with messages.

Actors induce a certain paradigm for your application, and I believe Go just wants to give you the tool to build whatever you want. Having channels allows using the Actor paradigm, the other way is not as easy/lightweight.

rubiquity2• 12 years ago

Actors are more like a combination of a channel and a goroutine: when you send something to the actor, you know what the other end is and you know what it does with messages.

I don't think this is the case at all. When sending a message to an address you don't know how many actors are behind that address, and even further you don't know how many addresses an actor has. Actors and addresses have a many-to-many relationship.

I think the power of the Actor model is essentially putting your faith in the system and not caring about when messages get handled, or what order they get handled in - it's just knowing that the message will get handled.

rubiquity2• 12 years ago

As described by Carl Hewitt, the inventor of the Actor model:

- CSP uses named channels (coincidentally called channels in Go) with anonymous processes (goroutines in Go)

- Actors are anonymous channels (mailbox addresses) with named processes (actors).

Carl Hewitt states that CSP was created to create a concurrency model around algebra and having named channels was the only way to accomplish that due to the constraints of algebra.

The Actor model's foundation is in physics. Here's an excellent video of Carl Hewitt giving an off the cuff explanation of the Actor Model[0], and some notes I took while watching it[1] (please add more notes if you can, I get confused about this topic constantly).

Another important note is that there are many different implementations of CSP but only one implementation of the Actor model.

0 - http://channel9.msdn.com/Shows/Going+Deep/Hewitt-Meijer-and-...

1 - https://gist.github.com/rbishop/9082539

4ad• 12 years ago

This (and pretty much all the other libraries) misses the point of Go/CSP channels completely. The select/alt statement. Channels are just queues. Queues are useful in any language. The power and ease of use of Go concurrency primitives don't come from channels and goroutines, it comes from the select statement.

mrphoebs8• 12 years ago

I'm not an expert at Go but what is the power that select gives. Don't higher order channel structures like multiplexing achieve something similar. Can you throw more light on this?

dsymonds• 12 years ago

The 'select' statement does more than just multiplex (and it doesn't really multiplex since you can't do it over a slice of channels). It allows blocking on any one of a set of send or receive operations. This is similar to the select(2) system call in BSD

Spec: http://golang.org/ref/spec#Select_statements

eternalban3• 12 years ago

Go is not really CSP anymore. The scheduler pre-empts.

You're right regarding this (pointless?) wrapper around Doug Lea's queues. If the OP really wants the kudos for doing CSP on Java, s/he'll need to tame the NIO selectors and no doubt sprinkle a little ASM magic dust on it as well.

Closest thing we have is Kilim (which is just simply awesome.)

scotth2• 12 years ago

For those who haven't seen Kilim:

http://www.malhar.net/sriram/kilim/

https://github.com/kilim/kilim

pron• 12 years ago

Actually, the closest we've got is Quasar[1] (I'm the main author). It's got true lightweight threads (goroutines), as well as selectable channels. On top, it's got actors, complete with selective receives and hot code-swapping.

It is much more actively maintained than Kilim, more general, and has better performance to boot. Also, Quasar fibers interoperate very nicely with plain threads. Blocking operations (such as channel receive) block the thread if you're running in a plain thread, and the fiber if you're running in a fiber.

In fact, we've even had time-sliced preemptive scheduling, which we've taken out because it didn't give performance benefits to fibers that block a lot, and for computations that don't, there's full blown threads (which Go doesn't have).

[1] https://github.com/puniverse/quasar

manishsharan• 12 years ago

I found Kilim to be an overkill for the most of my use cases. Instead I recommend checking out jetlang, https://code.google.com/p/jetlang/.) ( This implements message based concurrency, similar to Scala. I am using this in production code without any issues.I found this easier to implement than Kilim and delivers equivalent functionality

fauigerzigerk2• 12 years ago

What's the difference to java.util.concurrent.BlockingQueue?

mrphoebs8• 12 years ago

It's not pass by reference, it's pass by value. And also I like this abstraction better.

scotth2• 12 years ago

Wow. Sounds like some serious overhead.

fauigerzigerk2• 12 years ago

I see. I'm afraid in a mutable world that causes all kinds of serialization issues and unpredictable performance. Java developers are not used to knowing their object graphs very well.

ap22213• 12 years ago

What is a case in which you'd want pass by value in a queue? I mean sometimes you're forced to pass by value, but if you have the option of pass by reference, why would you choose by value?

Maybe I've been doing this stuff too long, but it's not all that hard to make an object safe for concurrency. But, I am probably missing some context.

vishal_biyani• 12 years ago

Spring integration project has similar concept of channels and you can use declarative model to connect channels and components & of course can do much more. What are any differences if you have context of Spring Integration?

mrphoebs8• 12 years ago

I had no idea such a thing existed, will check it out ,thanks. Can't comment on the differences, sorry.

baruch• 12 years ago

I was also inspired by Go channels and am working on a library in C that marries fibers, mostly blocking channels and a way to select on the channels.

You can find it in http://Github.com/Baruch/libwire

enscr• 12 years ago

What's flipkart incubator (the url is "flipkart-incubator.github.io"). I know flipkart is the Amazon of India.

mrphoebs8• 12 years ago

It's flipkart's OpenSource software org on github to incubate projects that developers drive and graduate them to fully sponsered, flipkart opensource projects.

Tell HN: Lois - Golang like channels for Java

Related Stories