Spawn process thats loops and get stdout continuosly in ruby

Question

i need to spwan a program in a ruby script. This program periodically print a JSON and in the main script i need to intercept this and made calculation. Thanks

Something like this:

MAIN:
   Spawn a process
      //This generates stdout periodically
   //End call
   Intercept its stdout
   //REST of the code

How to? I need to use eventmachine? Somewhat?

I clarify with this code

timer = EventMachine.add_periodic_timer POLLING_INTERVAL do
    if memcached_is_running
      ld 'reading from device'
      begin

          IO.popen("HostlinkPollerLight -p #{SERIAL_PORT} -v #{SERIAL_BAUDRATE} -r #{MODEL_CONFIG} 2> /dev/null") do |payload|
                  $_data = JSON.parse payload.readlines[0]
          end


        if $data['success']

          memcache.set( MEMCACHE_DATA_KEY, _to_json( $data[ 'result' ], _mapping ))
          timer.interval = POLLING_INTERVAL
        else
          log_this " read fault: error_code #{$data['fault']}"
          timer.interval = FAULT_INTERVAL
        end
      rescue Errno::ENOENT
        log_this 'Unable to read  output'
      rescue JSON::ParserError
        log_this 'Malformed  data'
      end
    else
      timer.interval = FAULT_INTERVAL
      system("on_red_led.sh 2")
    end
    log_this "elapsed time: #{Time.now.to_f - delta}"
    ld "## end read: #{counter}"

    counter += 1
end

I need to spwan only one time the program opened with popen and get the stdout every time its print stdout.

Answer 1

The way I do this is, that I create a class, which creates a new Thread with infinite loop, which alters object's instance variable. Then I can access those variables via its getters. Example:

class Stopwatch
  def initialize
    @seconds = 0
  end

  def start
    @thread = Thread.new do
      loop {
        sleep(1)
        @seconds += 1
      }
    end
  end

  def seconds
    @seconds
  end

  def stop
    @thread.kill
  end

  def reset
    @seconds = 0
  end
end

stoper = Stopwatch.new
stoper.start

sleep(5)
stoper.seconds #=> 5