Running Multiple Programs at once

Question

How can I run various programs at once. I have a DHT22 sensor sending info to Pubnub, and the LED's program running so I can control the form Pubnub. How can I run both programs at the same time?

the code for the DHT22 sensor is:

import time
import sys
from pubnub import Pubnub
import Adafruit_DHT as dht

pubnub = Pubnub(publish_key='demo', subscribe_key='demo')
channel = 'pi-house'

def callback(message):
print(message)

#published in this fashion to comply with Eon
while True:
    h,t = dht.read_retry(dht.DHT22, 4)
    temp='{0:0.1f}'.format(t)
    hum='{0:0.1f}'.format(h)
    message = {'temperature': temp, 'humidity': hum}
    print 'Temp={0:0.1f}*C Humidity={1:0.1f}%'.format(t, h)
    pubnub.publish(channel=channel, message=message, callback=callback, error=callback)  

the code for the led's is:

import RPi.GPIO as GPIO
import time
import sys
from pubnub import Pubnub

GPIO.setmode(GPIO.BCM)

PIN_LIVING = 22
PIN_PORCH = 17
PIN_FIREPLACE = 27

GPIO.setup(PIN_LIVING,GPIO.OUT)
GPIO.setup(PIN_PORCH,GPIO.OUT)
GPIO.setup(PIN_FIREPLACE,GPIO.OUT)

FREQ = 100 # frequency in Hz
FIRE_FREQ = 30 #  flickering effect

# Duty Cycle (0 <= dc <=100)

living = GPIO.PWM(PIN_LIVING, FREQ)
living.start(0)

porch = GPIO.PWM(PIN_PORCH, FREQ)
porch.start(0)

fire = GPIO.PWM(PIN_FIREPLACE, FIRE_FREQ)
fire.start(0)

# PubNub

pubnub = Pubnub(publish_key='demo', subscribe_key='demo')

channel = 'pi-house'

def _callback(m, channel):
    print(m)

    dc = m['brightness'] *10

    if m['item'] == 'light-living':
        living.ChangeDutyCycle(dc)

    elif m['item'] == 'light-porch':
        porch.ChangeDutyCycle(dc)

    elif m['item'] == 'fireplace':
        fire.ChangeDutyCycle(dc)

def _error(m):
  print(m)

pubnub.subscribe(channels='pi-house', callback=_callback, error=_error)

try:
    while 1:
        pass
except KeyboardInterrupt:
    GPIO.cleanup()
    sys.exit(1)

Thanks!

Answer 1

If you want to run multiple programs at once from the command line, you can use & to run a command in the background:

$ python foo.py > foo.log &
$ python bar.py > bar.log &

However, if your ssh session ends, or you log out, those processes will be terminated. If you would like to keep your programs running after logging out, use nohup:

$ nohup python foo.py > foo.log &
$ nohup python bar.py > bar.log &

If you want to run programs at specific times, look into crontab:

$ man 5 crontab

If you need your programs to run at boot time, look into the System V init system.

Answer 2

1. How are you running the programs individually? Are you SSH-ing into your Pi? If so, then you can open two terminals and run them both separately. You can use the "python program-name.py" command.

2. Another option, is to combine the two codes into one program and run that, so that you are publishing on a channel "A" for the temperature and humidity, and subscribe on another channel "B" to receive commands for the lights in your house. PubNub python publish and subscribe are asynchronous, so they don't block on each other.

3. A 3rd option is to use Python-twisted, which handles threading, so you can have different threads for publish and subscribe.