payment_gateway_check.rb

module PaymentGatewayCheck
  @available = nil
  MUTEX = Mutex.new

  TASK = PeriodicTask.new(every: 5.seconds, run_immediately: !Rails.env.test?) do
    begin
      result = HTTParty.get ENV['PAYMENT_GATEWAY_PING_ENDPOINT']
      MUTEX.synchronize { @available = result.success? }
    rescue SystemCallError
      MUTEX.synchronize { @available = false }
    end
  end

  def available?
    MUTEX.synchronize { !!@available }
  end

  %i<run stop>.each { |m| define_method(m) { TASK.send(m) } }

  extend self
end

periodic_task.rb

class PeriodicTask
  def initialize(every:, run_immediately: true)
    @mutex          = Mutex.new
    @stop_next_tick = false
    block           = proc

    @thread = Thread.new do
      Thread.stop unless run_immediately

      while true
        block.call
        sleep every

        Thread.stop if @mutex.synchronize { @stop_next_tick }
      end
    end
  end

  def run
    @mutex.synchronize { @stop_next_tick = false }
    @thread.run
  end

  def stop
    @mutex.synchronize { @stop_next_tick = true }
  end
end