CanCan Benchmark

cancanbench.rb

require 'bundler'
Bundler.require

require 'cancancan'
require 'allocation_tracer'
require 'benchmark/ips'
require 'objspace'
require 'pp'

def memprof(name)
  GC.disable
  before = `ps -o rss -p #{Process.pid}`.split("\n").last.to_i
  trace = ObjectSpace::AllocationTracer.trace do
    10_000.times do
      yield
    end
  end
  after = `ps -o rss -p #{Process.pid}`.split("\n").last.to_i

  puts "[#{name}] Mem diff: #{(after - before).to_f/1024.0} MB"
  #puts "[#{name}] Trace:"
  #puts trace
  #puts
  GC.enable
  GC.start
end

class Ability
  include CanCan::Ability

  def initialize
    can [:read, :write], [:foo, :bar]
  end
end

case ARGV.shift
when "--ips"
  Benchmark.ips do |b|
    b.report("Array#flatten") { CanCan::Rule.new(nil, [:read, :write], [:foo, :bar], nil, nil, false) }
    b.report("Kernel#Array") { CanCan::Rule.new(nil, [:read, :write], [:foo, :bar], nil, nil, true) }

    b.compare!
  end
when "--match"
    ability = Ability.new
    rule = ability.send(:rules).first
    rule.expanded_actions = ability.send(:expand_actions, rule.actions)

    memprof("as-is") do
      rule = ability.send(:rules).first
      rule.expanded_actions = ability.send(:expand_actions, rule.actions)
      rule.relevant?(:read, :bar)
    end
else
  memprof("Array#flatten") { CanCan::Rule.new(nil, [:read, :write], [:foo, :bar], nil, nil, false) }
  memprof("Kernel#Array") { CanCan::Rule.new(nil, [:read, :write], [:foo, :bar], nil, nil, true) }
end

Gemfile

source 'http://rubygems.org'

gem 'cancancan', path: "~/github/cancancan"
gem 'allocation_tracer'
gem 'benchmark-ips'

Notes.md

I had to modify CanCan::Rule to be able to switch between the two code paths under test. I added a simple boolean flag as a final parameter and placed in a conditional like:

if use_flatten
  @actions = [actions].flatten
  @subjects = [subjects].flatten
else
  @actions = Array(actions)
  @subjects = Array(subjects)
end