Does Dir.glob("") {} find all files before execute block?

create_many_files.rb

#! /bin/env ruby

Dir.mkdir "dirs"
100.times do |i|
  puts i
  Dir.mkdir "dirs/#{i}"
  1000.times do |j|
    puts "#{i}/#{j}"
    Dir.mkdir "dirs/#{i}/#{j}"
    File.open("dirs/#{i}/#{j}/file", "w") do |io|
      io << rand.to_s
    end
  end
end

test.rb

#! /usr/bin/env ruby

# dtrace: print file opend by processes.
#   dtrace -n 'syscall::open*:entry { printf("%s %s",execname,copyinstr(arg0)); }'


puts RUBY_VERSION

5.times do

  first = true
  start = Time.now.to_f
  count = 0

  puts "---- block ----"
  Dir.glob("**/*") do |f|
    if first
      sleep ARGV[0].to_i if ARGV[0]

      puts "first: #{Time.now.to_f - start}"
      first = false
    else
      count += 1
    end
  end
  puts "last: #{Time.now.to_f - start} #{count}"


  first = true
  start = Time.now.to_f
  count = 0

  puts "---- each ----"
  Dir.glob("**/*").to_a.each do |f|
    if first
      sleep ARGV[0].to_i if ARGV[0]

      puts "first: #{Time.now.to_f - start}"
      first = false
    else
      count += 1
    end
  end
  puts "last: #{Time.now.to_f - start}  #{count}"

end