debugging_deadlocks_spec.rb

# Set up `use_transactional_tests: false` as a tag that turns off transactional tests for the spec.
# Wrapping each spec in a transaction prevents concurrent transactions within the spec.
# See https://guides.rubyonrails.org/testing.html#testing-parallel-transactions

RSpec.configure do |config|
  config.around(:each, use_transactional_tests: false) do |example|
    self.use_transactional_tests = false
    example.run
    self.use_transactional_tests = true
  end
end

it "causes deadlock?", use_transactional_tests: false do
  device = create(:device, push_notification_subscriptions: %w(cooksnap_reminder mentioned_in_comment moderation_message))

  threads = []
  threads << Thread.new do
    puts "START THREAD 1"
    DeviceCreationService.run(
      device.user, {
        access_token: device.access_token,# the service finds (then updates) an existing device with the given access_token
        token: "new token", # the device `token` attribute needs to be updated
        platform: device.platform,
        push_notification_subscriptions: ["tip_likers", "comment"] # the device subscriptions also need updating
      }
    )
  end

  threads << Thread.new do
    puts "START THREAD 2"
    sleep(0.07)
    DeviceCreationService.run(
      device.user, {
        access_token: device.access_token,
        token: "new token",
        platform: device.platform,
        push_notification_subscriptions: ["tip_likers", "comment"]
      }
    )
  end

  threads.each(&:join)
ensure
  # Need to perform manual clean up since transactional tests are disabled
  User.destroy_all
end