processi

With the help from Alain I just released rufus-lua 0.1.0.

This ruby gem talks to Lua via Ruby FFI. One could say it’s “embedding Lua”, as Lua is described as “Lua is a powerful, fast, lightweight, embeddable scripting language.”

I feel tempted by Lua, there’s the speed, the austerity and that javascript feeling.

Rufus-lua is not the first bridge between Lua and Ruby, there are also :

* http://rubyluabridge.rubyforge.org/
* http://raa.ruby-lang.org/project/ruby-lua

They are worth a look, but I was a bit disappointed, they are not available via ‘sudo gem install …’.

Rufus-lua is available via Rubygems, but since it’s a FFI thing, it needs to talk to the dynamic library packaging of Lua. Well, it’s not available by default, there’s some work involved (but not too much).

Something great about FFI is that it works for Ruby 1.8.6, Ruby 1.9.1 and JRuby (1.1.6) (and will work soon for Rubinius, its original platform).

Once liblua.dylib is on your system, along with rufus-lua (sudo gem install rufus-lua), you can play with code like :

require 'rubygems'
require 'rufus/lua'

s = Rufus::Lua::State.new

t = s.eval(%{
  return { message = { 'hello', 'from', 'Lua' },
    funk = function (x) return 2^x end }
})

p t['message'].to_a # => ["hello", "from", "lua"]
p t['funk'].call(8) # => 256.0

s.close

Well, it’s only a 0.1.0 release…

As rufus-lua is using FFI it’s slower at the “frontier”, here is a naive benchmark for computing a Fibonacci suite, with Fiber (Ruby 1.9) and Coroutines on the Lua side :

require 'benchmark'
require 'rubygems'
require 'rufus/lua'

RUBYFIBS = Fiber.new do
  n1 = n2 = 1
  loop do
    Fiber.yield n1
    n1, n2 = n2, n1+n2
  end
end

s = %{
  co = coroutine.create(function ()
    local n1 = 1; local n2 = 1
    while true do
      coroutine.yield(n1)
      n1, n2 = n2, n1+n2
    end
  end)
  return co
}

LUA = Rufus::Lua::State.new
LUAFIBS = LUA.eval(s)

N = 10_000
Benchmark.benchmark(' ' * 31 + Benchmark::Tms::CAPTION, 31) do |b|
  b.report('ruby') do
    N.times { RUBYFIBS.resume }
  end
  b.report('lua via ruby') do
    N.times { LUAFIBS.resume }
  end
  b.report('lua') do
    LUA.eval("for i = 0, #{N} do coroutine.resume(co) end")
  end
end

LUA.close

For the original. Running it on my board yields something along the lines of :

$ ruby19 test/bm_fiber.rb
                  user     system      total        real
ruby          0.050000   0.010000   0.060000 (  0.052032)
lua via ruby  0.180000   0.000000   0.180000 (  0.195411)
lua           0.010000   0.000000   0.010000 (  0.006394)

Well, nothing spectacular, that just states that it’s better to not cross the border too often : the “lua via ruby” bench has Ruby resuming the Lua coroutine 10_000 times and it’s costly.

rufus-lua,
on github : http://github.com/jmettraux/rufus-lua/
rdoc : http://rufus.rubyforge.org/rufus-lua/
the rest of rufus : http://rufus.rubyforge.org

lua : http://www.lua.org
ffi : http://kenai.com/projects/ruby-ffi/