Safe way to run threads on rails

async.rb

module Async
  ##
  # Run code in thread, handle exceptions, release DB connections
  #
  #   Async(:send_email) { Mailer.send }
  #
  def self.run(name)
    parent_t = Thread.current
    working_thread = Thread.new do
      begin
        # copy thread variables
        # Rails and some other libraries may save something in thread variables
        # such as Timezone and locale
        parent_t.keys.each do |key|
          next if key =~ /activerecord|activesupport|__recursive_key__/i
          Thread.current[key] = parent_t[key]
        end

        # make sure DB connection is closed
        ActiveRecord::Base.connection_pool.with_connection do
          yield
        end
      rescue => error
        Rails.logger.info "Error in thread!"
        Rails.logger.info(error.message)
        Rails.logger.info(error.backtrace.join("\n"))
        # Send exception to airbrake/sentry/raygun/newrelic/slack
      end
    end

    # Wait for code to finish in testing environment
    # to avoid race condition when you expect changes made by thread
    if Rails.env.test?
      working_thread.join
    end

    working_thread
  end
end

## USAGE:

Async.run do
  user.send_welcome_email!
  user.update!(welcome_email_sent: true)
end