dead_heap.rb

# extract dead objects from the heap

require 'json'
require 'set'

class Slot
  attr_reader :info, :address_to_slot

  def initialize info, address_to_slot
    @info            = info
    @address_to_slot = address_to_slot
    @marked          = false
  end

  def mark!
    @marked = true
  end

  def references
    @references ||= (info[__method__.to_s] || []).uniq.map { |a|
      address_to_slot[a]
    }.compact
  end

  def address; info[__method__.to_s]; end
  def root; info[__method__.to_s]; end
  def root?; info["type"] == "ROOT"; end
  def marked?; @marked; end
  def id; root? ? root : address; end
end

address_to_slot = {}
roots           = []
all_nodes       = []

File.open(ARGV.shift, 'r') do |f|
  f.each_line do |line|
    info = JSON.parse line
    slot = Slot.new info, address_to_slot
    all_nodes << slot
    if slot.root?
      roots << slot
    else
      address_to_slot[slot.address] = slot
    end
  end
end

def mark mark_stack
  seen = Set.new
  while obj = mark_stack.pop
    next if seen.include? obj
    seen << obj
    obj.mark!
    mark_stack.concat obj.references
  end
end

mark roots.dup
garbage = all_nodes.reject(&:marked?)
garbage.each do |g|
  puts JSON.dump(g.info)
end