The posted code starts two async Processes. The first publisher Process publishes data to the Queue, the second subscriber Process reads the data from the Queue and logs it to console.
To make sure the Queue is not accessed at the same time, before getting the data from the Queue, the subscribe function first executes lock.acquire(), then gets the data with data = q.get() and finally releases the lock with the lock.release() statement.
The same locking-releasing sequence is used in publish function. But I had to comment two lines since acquiring the lock in publish
function brings the script to halt. Why?
import multiprocessing, time, uuid, logging
log = multiprocessing.log_to_stderr()
log.setLevel(logging.INFO)
queue = multiprocessing.Queue()
lock = multiprocessing.Lock()
def publish(q):
for i in range(20):
data = str(uuid.uuid4())
# lock.acquire()
q.put(data)
# lock.release()
log.info('published: %s to queue: %s' % (data, q))
time.sleep(0.2)
def subscribe(q):
while True:
lock.acquire()
data = q.get()
lock.release()
log.info('.......got: %s to queue: %s' % (data, q))
time.sleep(0.1)
publisher = multiprocessing.Process(target=publish, args=(queue,))
publisher.start()
subscriber = multiprocessing.Process(target=subscribe, args=(queue,))
subscriber.start()
