Finding locations of most allocated objects

most_allocated_objects.rb

require 'objspace'

def self.show_allocations(&block)
  _ = ObjectSpace.trace_object_allocations &block
  ObjectSpace
    .each_object
    .to_a
    .filter_map do |obj|
      file = ObjectSpace.allocation_sourcefile obj
      line = ObjectSpace.allocation_sourceline obj
      file && ["#{file}##{line}", obj.class.inspect] # objects created outside of the allocation tracing
    end
    .tally
    .sort_by { -_1.last }
    .map { |(loc, klass), tally| [tally, klass, loc] }
end

def self.format_allocations(limit=10, allocations)
  rows = allocations.take(limit).each { _1[0] = _1[0].to_s.gsub(/(?<=.)(?=.{3}+$)/, ",") }
  width_n, width_class, width_loc = rows.transpose.map { _1.map(&:to_s).map(&:size).max }
  format = "%#{width_n}s | %#{width_class}s | %-#{width_loc}s\n"
  rows.map { format % _1 }.join("")
end

require 'json'
puts format_allocations show_allocations {
  [ 10_000.times.map { "a" },
    5_000.times.map { "b" },
    JSON.parse('{ "c": 123, "d": true, "e": "f" }'),
  ]
}

# >> 10,000 |            String | program.rb#27                                                     
# >>  5,000 |            String | program.rb#28                                                     
# >>      4 |            String | /Users/josh/.gem/ruby/3.0.2/gems/json-2.6.1/lib/json/common.rb#216
# >>      2 |             Array | program.rb#27                                                     
# >>      2 |              Hash | /Users/josh/.gem/ruby/3.0.2/gems/json-2.6.1/lib/json/common.rb#216
# >>      2 |              Hash | /Users/josh/.gem/ruby/3.0.2/gems/json-2.6.1/lib/json/common.rb#127
# >>      1 | JSON::Ext::Parser | /Users/josh/.gem/ruby/3.0.2/gems/json-2.6.1/lib/json/common.rb#216
# >>      1 |              Hash | /Users/josh/.gem/ruby/3.0.2/gems/json-2.6.1/lib/json/common.rb#215
# >>      1 |        Enumerator | program.rb#27                                                     
# >>      1 |            String | program.rb#29