Ben Holley benolee

Avoiding Hash Lookups in a Ruby Implementation

I had an interesting realization tonight: I'm terrified of hash tables. Specifically, my work on JRuby (and even more directly, my work optimizing JRuby) has made me terrified to ever consider using a hash table in the hot path of any program or piece of code if there's any possibility of eliminating it. And what I've learned over the years is that the vast majority of execution-related (as opposed to data-related, purely dynamic-sourced lookup tables) hash tables are totally unnecessary. Some background might be interesting here.

Hashes are a Language Designer's First Tool

$ jruby -v
jruby 1.7.0 (1.9.3p203) 2012-10-22 ff1ebbe on Java HotSpot(TM) 64-Bit Server VM 1.6.0_33-b03-424-10M3720 [darwin-x86_64]

$ time jruby -e 'require "rubygems"; require "active_support"'
real	0m1.426s
user	0m2.681s
sys	0m0.180s

$ export JAVA_OPTS='-d32'  # switch to 32-bit client mode

$ jruby -v

create a new dir

$ mkdir /tmp/ruby
$ cd /tmp/ruby

create extconf.rb

first, make the Makefile

$ ruby extconf.rb
creating Makefile

next, build the extension

	source :rubygems

	gem 'actionpack', '3.2.3'
	gem 'activerecord', '3.2.3'
	gem 'activesupport', '3.2.3'
	gem 'railties', '3.2.3'
	gem 'tzinfo'
	gem 'sqlite3'

	gem 'thin'

	[1] pry(main)> user = User.new
	=> #<User @id=nil @email=nil @encrypted_password=nil>
	[2] pry(main)> User.all
	=> [#<User @id=1 @email="[email protected]" @encrypted_password="$2a$05$7N1xabSr/SPFJuCKpm62nurvRgsF59GfKu3ZPnK9H9nlnkfytAC62">, #<User @id=2 @email="[email protected]" @encrypted_password="$2a$05$TkRn2veaV/uBEQp0912Vweb2Kf1dnX2DpyM5fk.8SgW7C/ufpwlK6">]
	[3] pry(main)> user.email = '[email protected]'
	=> "[email protected]"
	[4] pry(main)> user.password = 'secretpass'
	=> "secretpass"
	[5] pry(main)> user.save
	=> true

	require 'bundler/setup'
	Bundler.require :default

	require 'securerandom'
	require 'active_support/notifications'
	require 'active_support/concern'

	module Events
	include ActiveSupport::Concern

	>> require 'fiddle'
	=> true
	>> func = Fiddle::Function.new(DL::Handle::DEFAULT['rb_eval_string'], [DL::TYPE_VOIDP], DL::TYPE_VOIDP)
	=> #<Fiddle::Function:0x000001010404c8>
	>> func.call("1 + 1")
	=> #<DL::CPtr:0x00000101821930 ptr=0x00000000000005 size=0 free=0x00000000000000>
	>> func.call("1 + 1").to_value
	=> 2
	>> func.call("puts 'hello'").to_value
	hello

	.out {
	color: red;
	font-family: 'Inconsolata', sans-serif;
	}