线程化-具有Counter对象的生产者/消费者

Question

I have written a code snippet below that aims to achieve the following. I have a counter object that is shared between all of the consumers, these consumers, upon completion of their task, increment the counter and wait patiently. The idea is to create a new ip address that the other threads can then use in their new task, this will be done by the producer, who also checks if the counter is of some value, and if it is, it will create a new ip and notify everyone, otherwise notify everyone without creating a new ip. But for some reason, I never get the NOT SETTING A NEW IP ADDRESS message. Can someone tell me why?

Thanks a bunch:

import logging
import threading
import time
import random

class Counter(object):

    def __init__(self, start=0):
        self.lock = threading.RLock()
        self.value = start

    def increment(self):
        logging.debug('Waiting for lock')
        with self.lock:
            logging.debug('Acquired lock. Current counter value: {}'.format(self.value + 1))
            self.value = self.value + 1

def consumer(cond, counter):
    """wait for the condition and use the resource"""
    logging.debug('Starting consumer thread')
    while True:
        time_sleep = random.randint(5, 10) / 5
        time.sleep(time_sleep)
        with cond:
            counter.increment()
            logging.debug('Resource is available to consumer. Doing some werk on counter {}'.format(counter.value))
            logging.debug('Done some werk. Waiting for other threads to finish their werk and for producer to signal continuation.')
            cond.wait()


def producer(cond, counter):
    """set up the resource to be used by the consumer"""
    logging.debug('Starting producer thread')

    for i in range(4):
        logging.debug('Producer sleeping for 3 seconds')
        time.sleep(3)
        with cond:
            if counter.value % 2 == 0:
                logging.debug('Setting a new ip address')
                cond.notifyAll()
            if counter.value % 2 != 0:
                logging.debug('NOT SETTING A NEW IP ADDRESS')
                cond.notifyAll()


logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s (%(threadName)-2s) %(message)s',
)

condition = threading.Condition()
c = Counter()

c1 = threading.Thread(name='c1', target=consumer,
                      args=(condition, c))
c2 = threading.Thread(name='c2', target=consumer,
                      args=(condition, c))
p = threading.Thread(name='p', target=producer,
                     args=(condition, c))

c1.start()
c2.start()

p.start()

Answer 1

Try adding a lock inside the producer thread.

Other thread should wait for the producer to do its task.

This prevents counter being overwritten by the other thread during the execution of producer thread.

def producer(cond, counter):
    """set up the resource to be used by the consumer"""
    logging.debug('Starting producer thread')
    with self.lock
    for i in range(4):
        logging.debug('Producer sleeping for 3 seconds')
        time.sleep(3)
        with cond:
            if counter.value % 2 == 0:
                logging.debug('Setting a new ip address')
                cond.notifyAll()
            if counter.value % 2 != 0:
                logging.debug('NOT SETTING A NEW IP ADDRESS')
                cond.notifyAll()