Little ruby test script to make sure that Redis SET NAME VALUE NX:TRUE locking really works

there-can-be-only-one.rb

#!/usr/bin/env ruby
#
require 'redis'
require 'securerandom'
require 'awesome_print'

class RedisTest
  attr_reader :name, :redis

  HOW_MANY = (1..5)

  def initialize(name)
    @name = name
    @redis = Redis.new
    delete_lock(quiet: true)
  end

  def run_tests
    [:serial_test, :parallel_test].each do |test_name|
      warn "Running #{test_name}:"
      send(test_name)
    end
  end

  def serial_test
    delete_lock
    if HOW_MANY.map { locked? }.one?
      puts 'ok'
    else
      warn "Serial lock test failed!"
    end
  end

  def parallel_test
    delete_lock
    if run_many { locked? }.one?
      puts 'ok'
    else
      warn "Parallel lock test failed!"
    end
  end

  def run_many
    outfiles = []
    HOW_MANY.map { outfiles << fork_one { yield } }
    Process.waitall
    outfiles.map do |file|
      file.rewind
      file.read.chomp == "true"
    end
  ensure
    outfiles.each { |file| file.unlink }
  end

  def fork_one
    outfile = Tempfile.new
    fork { outfile.puts yield }
    outfile
  end

  def locked?
    try_lock && read_lock == my_uuid
  end

  def read_lock
    redis.get lock_name
  end

  def try_lock
    redis.set lock_name, my_uuid, nx: true
  end

  def delete_lock(quiet: false)
    if redis.del(lock_name) != 1
      warn "lock #{lock_name} deletion failed!" unless quiet
    end
  end

  def lock_name
    @lock ||= name + '-lock'
  end

  def my_uuid
    @uuid ||= SecureRandom.uuid
  end
end

RedisTest.new('redis-test').run_tests