Kind of depressing how far behind Ruby is from V8, Hotspot, CLR etc in terms of the sophistication of the GC, non-existent JIT etc. Still hoping someday someone will make the investment needed to catch up.
I would like to read an actual in-depth comparison. While undeniably the quality of the Ruby implementation has a long way to go, Ruby has very "loose" semantics and I think some of the optimizations that are possible for Java, JavaScript or even for Smalltalk are simply not possible for Ruby because you have less assumptions to rely upon, everything has to be looked up at runtime basically.
Besides just nitty-gritty optimizations there are some high level design issues which are interesting. JVM performance is great for languages like Java, but for some reason probably related to the JVM all Java web servers seem to be multi-threaded monsters, which turns debugging into a mess and seems to make DoS attacks way easier. We use a self-hosted Jira on top of Tomcat at work, there are maybe 30 simultaneous users and every time one of them does something computationally expensive or uses some buggy functionality the whole process goes nuts, memory leaks until exhaustion, load goes to maximum etc., the whole web sever has to be restarted. With a web server with multiple worker processes you just restart the single worker and call it a day. Does anyone happen to know why the worker-based hosting model with separate worker processes seems to be completely absent from the Java world in favour of multi-threaded servers?
I seem to remember a discussions about this a decade ago, with smalltalkers saying that the only big difference is that programmatic generation of code is not so common in ST as it is in ruby (i.e. "attr_*" is possible in ST but doesn't actually exist).
Other than that I _think_ maybe ST has a fixed number of slots per class compared to dynamically added instance/class variables in ruby? My memory is fuzzy.
By the way, there _is_ a ruby built by smalltalk developers[0] exactly because the object model is 99% the same.
I don't know Smalltalk well enough to say for sure, it's just my rather vague impression that Smalltalk is more compiler-friendly, likely based mostly on what I've read over the years about this, for example looking at:
Ruby permits adding methods to individual objects; in Smalltalk, all methods reside in classes.
In Ruby, it is practical and somewhat useful to add methods dynamically; in Smalltalk, the practice is generally to treat the methods and classes as static.
> Ruby permits adding methods to individual objects; in Smalltalk, all methods reside in classes.
All Ruby methods reside in classes, too, "adding a method to an object" is really adding it to the object's singleton class (metaclass).
The difference between Ruby and Smalltalk is that in Smalltalk, each explicit class has an implicit metaclass (a class in which the class's instance methods are defined), whereas for Ruby each object (including, but not limited to, class objects -- and notably including other implicit metaclasses) has an implicit metaclass (often called the eigenclass).
And note that Ruby eigenclasses are in effect perfectly normal classes, with the exceptions that: 1) they dynamically get created the first time you define a method on it, 2) they are then "injected" into the inheritance chain, yet hidden from you when you try to follow the inheritance chain.
In effect, from an implementation point of view (at least for MRI), they're just normal classes except for when you define them, and a handful of insignificant cases where you have to check a flag to determine whether or not to consider them.
I wrote that one in frustration when working on my Ruby compiler project, actually, and I think there are reasonable solutions to all of them, and in fact you will find that most of them, possibly all are solved to various extents in either Smalltalk implementations or Self implementations. In particular the Self papers is an invaluable resource for anyone who wants to implement languages as dynamic as Ruby, or Javascript...
The main problem is the effort. And implementations like MRI really has not tried very hard to address any of this - you'll note it first got a bytecode version (instead of AST walking) with 1.9, and still does not JIT. AFAIK they've not even tested simple optimizations like partial vtables to avoid the costly method dispatch etc.
A big part of the challenge is that Ruby is a remarkably hard language to implement, not just or even mainly because of the dynamic features - those make it hard to make it fast, not hard to implement - but because it's still largely unspecified, the parsing is chock full of annoying corner cases, and there are lots of dark, hairy areas of Ruby that almost nobody ever see. I love Ruby, but I think it badly needs
a revision that deprecates a whole chunk of functionality that nobody really uses but that affects implementations, as well as writing a proper spec and then tighten up a whole lot of areas where users would be largely unaffected, but that would make it vastly easier to implement.
So a lot of effort that could have gone into making implementations faster, go into addressing annoying digressions.
Being the one widely supported client-side language for the web means that lots more money has been poured into making JavaScript implementations effective than has gone into Ruby (I wouldn't be surprised if Google put more resources into V8 than have gone into all Ruby implementations combined.)
True, but since V8 is open-source, shouldn't it now be possible for the Ruby developers to borrow the techniques from it that made Javascript so much faster?
None of the techniques that's gone into V8 are all that novel. Most of them - at least the ones that are relevant to Ruby - stems from research around Smalltalk and Self that's been well known for a very long time. The hard/time consuming part is implementing them.
Ruby isn't JavaScript. Studying V8's solutions to particular problems with making JavaScript efficient may help people seeking to make an efficient Ruby implementation, but how much is easily transferrable I don't know.
No doubt V8 is much more mature than MRI, I think some language considerations do still apply though, JavaScript doesn't have method_missing, problem #5 doesn't apply, I guess there is more.
Because there's always something different that needs to be done for them once your project starts becoming non-trivial. You might need a different version of a gem (e.g. pure-java Nokogiri), or they're behind recent MRI features. And if you care about concurrency, it's different everywhere.
In my personal experience I've found MRI to be the best experience simply because that's what most other people are using, and there's a lot to be gained from being in the mainstream.
Don't get me wrong- I would actually love for JRuby to become the de-facto Ruby implementation. So many headaches are caused by native code in gems. And we'd have a solid foundation for GC, concurrency, etc. But that's not the current reality.
Rubinius does not need Gem replacements like you need in JRuby, it still has a compatible CAPI.
> [...] or they're behind recent MRI features.
Part of this is due to MRI having literally no specification process at all. Python has the PEP system, no such thing exists in Ruby land. People tried to change this in the past (http://rubyspec.org/design/) but with little to no success so far. As a direct result of this there are only two ways to keep up to date with what changes in Ruby:
1. Follow every issue reported on bugs.ruby-lang.org, forever.
2. Wait until users report issues about something not being present, behaving differently, etc.
> And if you care about concurrency, it's different everywhere.
This is FUD. An implementation may offer different primitives for concurrency (e.g. Rubinius has Rubinius::Channel) but they also offer shared APIs. For example, the Thread class works across all implementations as you'd expect. Whether you use this on JRuby or Rubinius the end result is the same: proper concurrency.
For me it's always the triple-whammy of being a bit (or a lot) slower, needing vastly more memory, and having astronomical startup times. Not exactly an appealing combination.
If you're seeing a situation where you need vastly more memory with JRuby, please file it. While there is a higher base memory footprint due to the JVM being booted, I've found in practice it's much better on RAM than MRI. We saved a lot of money on EC2 by switching to JRuby because servicing a new request with a thread was a lot cheaper than forking a process running Rails.
I think the problem with no Ruby JIT stern from the fact there are no Ruby design spec. We have implementation and no standard. Compared to Javascript and Lua, Python or Java.
Ruby may not ever catch up to the superfast LuaJIT or Javascripts V8 performance due to the nature of the languages itself. But that doesn't mean Ruby should be an order of magnitude slower then them.
