python threading具有线程安全性的队列生产者 - 消费者

Question

我正在使用线程和队列来获取URL并存储到数据库.
我只想要一个线程来做存储工作.
所以我写代码如下:

import threading
import time

import Queue

site_count = 10

fetch_thread_count = 2

site_queue = Queue.Queue()
proxy_array=[]        


class FetchThread(threading.Thread):
    def __init__(self,site_queue,proxy_array):
        threading.Thread.__init__(self)
        self.site_queue = site_queue
        self.proxy_array = proxy_array
    def run(self):
        while True:
            index = self.site_queue.get()
            self.get_proxy_one_website(index)
            self.site_queue.task_done()
    def get_proxy_one_website(self,index):
        print '{0} fetched site :{1}\n'.format(self.name,index)
        self.proxy_array.append(index)


def save():
    while True:
        if site_queue.qsize() > 0:
            if len(proxy_array) > 10:
                print 'save :{0}  to database\n'.format(proxy_array.pop())

            else:
                time.sleep(1)
        elif len(proxy_array) > 0:
            print 'save :{0} to database\n'.format(proxy_array.pop())

        elif len(proxy_array) == 0:
            print 'break'
            break
        else:
            print 'continue'
            continue

def start_crawl():
    global site_count,fetch_thread_count,site_queue,proxy_array
    print 'init'
    for i in range(fetch_thread_count):
        ft = FetchThread(site_queue,proxy_array)
        ft.setDaemon(True)
        ft.start()

    print 'put site_queue'
    for i in range(site_count):
        site_queue.put(i)

    save()

    print 'start site_queue join'
    site_queue.join()
    print 'finish'

start_crawl()

出口产量:

init
put site_queue
Thread-1 fetched site :0

Thread-2 fetched site :1

Thread-1 fetched site :2

Thread-2 fetched site :3

Thread-1 fetched site :4

Thread-2 fetched site :5

Thread-1 fetched site :6

Thread-2 fetched site :7

Thread-1 fetched site :8

Thread-2 fetched site :9

save :9 to database

save :8 to database

save :7 to database

save :6 to database

save :5 to database

save :4 to database

save :3 to database

save :2 to database

save :1 to database

save :0 to database

break
start site_queue join
finish
[Finished in 1.2s]

为什么save()函数运行之后site_queue.join()写的save().
我也save() 用线程函数代替了,但它也不起作用.
这是否意味着我必须改变proxy_array=[]对proxy_queue=Queue.Queue(),然后我可以使用theading存储数据？
我只想要一个thead这样做,并且没有任何其他theads会从中获取数据proxy_array,我为什么要加入它？使用Queue似乎很奇怪.
有没有更好的解决方案？

更新:
我不想等到所有的FetchThreads完成他们的工作.我想在fraccing时保存数据,它会快得多.我希望结果如下所示(因为我使用array.pop(),所以保存0可能会出现得很晚,这只是一个容易理解的例子.):

Thread-2 fetched site :1

Thread-1 fetched site :2

save :0 to database

Thread-2 fetched site :3

Thread-1 fetched site :4

save :2 to database

save :3 to database


Thread-2 fetched site :5

Thread-1 fetched site :6

save :4 to database
.......

UPDATE2对某人有同样的问题如下:

问题:
正如我在上面所说的那样,没有任何其他的theads会从proxy_array获取数据.
我无法想象为什么它会破坏线程安全？

回答:
生产者 - 消费者问题在misha的回答中,我仔细阅读后理解.

问:
还有一个问题,如果程序主线程可以像FetchThreads一样扮演comsumer(换句话说,不需要创建StoreThread)

这是我无法弄清楚的,我会在找到答案后更新.

Answer 1

我必须提出类似的生产者 - 消费者.生产者生成一个'id',消费者使用该id来进行一些url获取并将其处理到它.这是我的骨架代码

    import Queue
    import random
    import threading
    import time
    import sys

    data_queue = Queue.Queue()
    lock = threading.Lock()

    def gcd(a, b):
        while b != 0:
            a,b = b, a%b

        return b

    def consumer(idnum):
        while True:
            try:
                data = data_queue.get(block=False)
            except Exception, e:
               print 'Exception ' + str(e)
            else:
                with lock:
                    print('\t consumer %d: computed gcd(%d, %d) = %d' %(idnum, data[0], data[1], gcd(data[0], data[1])))

            time.sleep(1)
            data_queue.task_done()

    def producer(idnum, count):
        for i in range(count):
            a,b = random.randint(1, sys.maxint), random.randint(1, sys.maxint)
            with lock:
                print('\t producer %d: generated (%d, %d)'% (idnum, a, b))
            data_queue.put((a,b))
            time.sleep(0.5)

    if __name__ == '__main__':
        num_producers = 1
        num_consumers = 2
        num_integer_pairs = 10

        for i in range(num_consumers):
            t = threading.Thread(target=consumer, args=(i,))
            t.daemon = True
            t.start()

        threads = []
        for ii in range(num_producers):
            thread = threading.Thread(target=producer, args=(ii, num_integer_pairs))
            threads.append(thread)
            thread.start()

        # wait for the producers threads to finish
        for thread in threads:
            thread.join()
        print 'done with producer threads'

        # wait till all the jobs are done in the queue
        data_queue.join()

        with lock:
            print 'all consumer threads finished'

        with lock:
            print 'main thread exited'