Demo of basic producer/consumer just for fun.

basic-producer-consumer.py

# In this program there is a queue implemented as a list protected by a
# mutex so that the producer can run on one thread and the consumer can
# run on another thread. The dequeue_all method will return an empty list
# if there is no work (it does not block its caller).

from random import random
from random import shuffle
from time import sleep
from threading import Lock
from _thread import start_new_thread
from sys import version_info

# sanity check Python version
assert(version_info >= (3,7))

lock = Lock()
queue = []

def enqueue(x):
  lock.acquire()
  queue.append(x)
  lock.release()

def dequeue_all():
  lock.acquire()
  xs = queue.copy() # duplicate queue value because we want to return the value after clearing the queue in the next line
  queue.clear()
  lock.release()
  return xs

def produce():
  while True:
    sleep(random());
    colours = ["red","orange","yellow","green","blue","indigo","violet"]
    shuffle(colours) # eek! updates in-place
    x = colours[0]
    print("about to add "+str(x)+" to the queue")
    enqueue(x)

# run producer as a background thread
start_new_thread(produce, ())

# give producer a five second head start
sleep(5)

# consume from the queue on the main thread
while True:
  xs = dequeue_all()
  print("got "+str(xs)+" off the queue")
  sleep(0.1 * random()) # delay a little bit to reduce lock contention

# run for five more seconds
sleep(5)