Useful script to help debugging memory leaks

find_needles_in_haystack.rb

# This script is taken from https://github.com/rails/rails/issues/32892#issuecomment-423376552

require 'ap'
require 'json'
require 'set'
require 'cgi'
require 'byebug'

class Slot
  attr_reader :info, :address_to_slot

  def initialize info, address_to_slot
    @info            = info
    @address_to_slot = address_to_slot
    @can_reach       = {}
  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 reachable? addr, seen = Set.new
    return if seen.include?(address)

    seen << address

    @can_reach.fetch(addr) do
      reachable = address == addr || references.any? { |ref|
        ref.reachable?(addr, seen)
      }

      @can_reach[addr] = reachable
    end
  end

  def marked?; @can_reach.values.any?; end
  def id;      root? ? root : address; end

  def label
    attributes = %w{ type name file line }.map { |key| info[key] }.compact.map { |k|
      CGI.escape_html(k.to_s)
    }.join " | "
    extras = ''
    if @can_reach[address]
      extras = "style=bold fontsize=30 fontcolor=red color=red"
    end
    "#{id.inspect} [label=\"{ #{id} | #{attributes} }\"#{extras}];"
  end

  def inspect
    info
  end

  def to_s
    address
  end
end

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

STDERR.puts "Building tree..."

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

STDERR.puts "Searching needles..."

def reachable?(address)
  STDERR.puts "  #{address}"
  address = address.gsub(/x[0]+/, 'x')
  STDERR.puts "    #{address} not found in tree" unless $address_to_slot[address]
  $roots.map { |root| root.reachable?(address) }.any?
end

ARGV.each do |needle|
  reachable? needle
end

STDERR.puts "Generating dot file..."

puts "digraph g {"
puts "node [shape=record];"

empty = true

$all_nodes.each do |node|
  next unless node.marked?
  puts node.label
  node.references.each do |ref|
    next unless ref.marked?
    empty = false
    puts "#{node.id.inspect} -> #{ref.id.inspect}"
  end
end

puts "}"

STDERR.puts "  dot file empty" if empty