gc_test.rb

# hacking some lines to get into the ruby object allocation process...

# Enable the GC profiler:
GC::Profiler.enable

# If our test create too many objects forcing the GC to run, 
# we can disable the GC to properly see the object allocation
# GC.disable

def count_string_allocations
  strings_before = count(:T_STRING)
  yield if block_given?
  strings_after  = count(:T_STRING)
  # let's not create a new string and get the counter confused ;)
  # "\n\tstring count: #{strings_after - strings_before}"
  strings_after - strings_before
end

def count(type)
  ObjectSpace.count_objects[type]
end

def gc_cost(&block)
  GC.start # run the GC on the previously allocated objects
  yield
  GC.start # run the GC on the allocated objects
  puts GC::Profiler.result
  GC::Profiler.clear
end

puts "#{count_string_allocations {}} strings in memory before starting the test" #rampup
puts "Strings created using a symbol: #{count_string_allocations{ 100.times{ :hello } }}"
puts "Strings created using a string: #{count_string_allocations{ 100.times{ "hello" } }}"

puts "Cost of running the GC"
gc_cost{ 10_000.times { print '.' } }

# install builder if not already available ($ gem install builder)
require 'builder'
puts "Cost of running the GC on 1 builder object"
gc_cost do
  builder = Builder::XmlMarkup.new
  xml = builder.person { |b| b.name("Matt"); b.phone("555-1234") }
end

puts "ouch..."