Benchmark for fix in ActiveSupport

benchmark.rb

require 'json'
require 'active_support/all'

#
# Monkeypatch Hash class in order to be able to compare both version
#
class Hash
  def as_json(options = nil) #:nodoc:
    # create a subset of the hash by applying :only or :except
    subset = if options
      if attrs = options[:only]
        slice(*Array(attrs))
      elsif attrs = options[:except]
        except(*Array(attrs))
      else
        self
      end
    else
      self
    end

    if $patched
      # updated version
      result = {}
      subset.each do |k, v|
        result[k.to_s] = options ? v.as_json(options.dup) : v.as_json
      end
      result
    else
      # previous version
      Hash[subset.map { |k, v| [k.to_s, options ? v.as_json(options.dup) : v.as_json] }]
    end
  end
end

# Actual benchmark code

def build_random_hash(number, nesting=0)
  return number if nesting == 0
  number.times.map{|i|
    [i, build_random_hash(number, nesting - 1)]
  }.to_h
end

def compare(hash)
  GC.start
  $patched = true
  allocated_before = GC.stat(:total_allocated_objects)
  hash.as_json
  allocated_after = GC.stat(:total_allocated_objects)
  patched = "Object count after patch: #{allocated_after - allocated_before}"

  GC.start
  $patched = false
  allocated_before = GC.stat(:total_allocated_objects)
  hash.as_json
  allocated_after = GC.stat(:total_allocated_objects)
  not_patched = "Object count before patch: #{allocated_after - allocated_before}"

  puts patched
  puts not_patched
end

compare build_random_hash(1, 1)
compare build_random_hash(1, 10)
compare build_random_hash(3, 3)
compare build_random_hash(5, 5)