Simulate race condition during backup collage upload

collage_struct_template.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>scraps</key>
	<array>
		<dict>
			<key>image</key>
			<dict>
				<key>source_url</key>
				<string>race_condition</string>
			</dict>
			<key>scrap_type</key>
			<string>image</string>
		</dict>
	</array>
</dict>
</plist>

simulate_race_condition.rake

# frozen_string_literal: true

# This contains destructive operations, so run with RAILS_ENV=test
# Usage:
# 1. Copy the file collage_struct_template.plist to project root
# 2. Run setup: `rake race_condition:setup`
# 3. Run script: `rake race_condition` 

desc 'race condition setup'
task 'race_condition:setup' do
  `mkdir race_condition 2>/dev/null`
  `mkdir race_condition/prep 2>/dev/null`
  10.times do |n|
    `cat collage_struct_template.plist | sed "s/race_condition/&#{n}/" > race_condition/prep/#{n}.plist`
  end
end

desc 'simulating race condition'
task race_condition: :environment do
  # =============================
  # Arrange

  puts 'Resetting DB tables'
  ActiveRecord::Base.connection.execute('TRUNCATE assets RESTART IDENTITY')
  ActiveRecord::Base.connection.execute('TRUNCATE collages RESTART IDENTITY')

  puts 'Creating collages'
  n = 10

  cids_with_index = n.times.each_with_object({}) do |num, memo|
    struct_json = CB::Plist.parse(File.open("race_condition/#{num}.plist").read).to_json
    memo[num] = Collage.create!(struct_json: struct_json).id
  end
  puts "Preparation done. Created #{n} collages."

  # =============================
  # Act

  puts 'Creating thumbnanil and assets'

  cids_with_index.each do |idx, cid|
    metadata = { 'collage_id' => cid }
    [
      Thread.new { ImageAsset.create!(provenance: ImageAsset::Provenance::COLLAGE_THUMBNAIL, metadata: metadata) },
      Thread.new { ImageAsset.create!(client_side_name: "race_condition#{idx}", provenance: ImageAsset::Provenance::COLLAGE_ASSET, metadata: metadata) }
    ].each(&:join)
  end

  # =============================
  # Observe

  cs = Collage.all
  non_downloadables = cs.reject(&:is_downloadable)
  puts '[Result]'
  puts "- # of all collages: #{cs.count}"
  puts "- # of non_downloadables: #{non_downloadables.count}"

  puts "\nRecalculating..."
  still_non_downloadables = non_downloadables.count do |c|
    c.update(is_downloadable: c.calculate_is_downloadable)
    !c.is_downloadable
  end

  puts "- # of non_downloadable collages: #{still_non_downloadables}"
end