Queue是python中的標準庫，可以直接import Queue引用;佇列是執行緒間最常用的交換資料的形式

python下多執行緒的思考

對於資源，加鎖是個重要的環節。因為python原生的list,dict等，都是not thread safe的。而Queue，是執行緒安全的，因此在滿足使用條件下，建議使用佇列

1. 初始化： class Queue.Queue(maxsize) FIFO 先進先出

2. 包中的常用方法:

   • Queue.qsize() 返回佇列的大小

   • Queue.empty() 如果佇列為空，返回True,反之False

   • Queue.full() 如果佇列滿了，返回True,反之False

   • Queue.full 與 maxsize 大小對應

   • Queue.get([block[, timeout]])獲取佇列，timeout等待時間

3. 建立一個“佇列”物件

   • import Queue
   • myqueue = Queue.Queue(maxsize = 10)

4. 將一個值放入佇列中

   • myqueue.put(10)

5. 將一個值從佇列中取出

   • myqueue.get()

多執行緒示意圖

# -*- coding:utf-8 -*-
import requests
from lxml import etree
from Queue import Queue
import threading
import time
import json


class thread_crawl
 
(threading.Thread):
    '''
    抓取執行緒類
    '''

    def __init__(self, threadID, q):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.q = q

    def run(self):
        print "Starting " + self.threadID
        self.qiushi_spider()
        print "Exiting ", self.threadID

    def
 
 qiushi_spider(self):
        # page = 1
        while True:
            if self.q.empty():
                break
            else:
                page = self.q.get()
                print 'qiushi_spider=', self.threadID, ',page=', str(page)
                url = 'http://www.qiushibaike.com/8hr/page/' + str(page) + '/'
                headers = {
                    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36',
                    'Accept-Language': 'zh-CN,zh;q=0.8'}
                # 多次嘗試失敗結束、防止死迴圈
                timeout = 4
                while timeout > 0:
                    timeout -= 1
                    try:
                        content = requests.get(url, headers=headers)
                        data_queue.put(content.text)
                        break
                    except Exception, e:
                        print 'qiushi_spider', e
                if timeout < 0:
                    print 'timeout', url


class Thread_Parser(threading.Thread):
    '''
    頁面解析類；
    '''

    def __init__(self, threadID, queue, lock, f):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.queue = queue
        self.lock = lock
        self.f = f

    def run(self):
        print 'starting ', self.threadID
        global total, exitFlag_Parser
        while not exitFlag_Parser:
            try:
                '''
                呼叫佇列物件的get()方法從隊頭刪除並返回一個專案。可選引數為block，預設為True。
                如果佇列為空且block為True，get()就使呼叫執行緒暫停，直至有專案可用。
                如果佇列為空且block為False，佇列將引發Empty異常。
                '''
                item = self.queue.get(False)
                if not item:
                    pass
                self.parse_data(item)
                self.queue.task_done()
                print 'Thread_Parser=', self.threadID, ',total=', total
            except:
                pass
        print 'Exiting ', self.threadID

    def parse_data(self, item):
        '''
        解析網頁函式
        :param item: 網頁內容
        :return:
        '''
        global total
        try:
            html = etree.HTML(item)
            result = html.xpath('//div[contains(@id,"qiushi_tag")]')
            for site in result:
                try:
                    imgUrl = site.xpath('.//img/@src')[0]
                    title = site.xpath('.//h2')[0].text
                    content = site.xpath('.//div[@class="content"]/span')[0].text.strip()
                    vote = None
                    comments = None
                    try:
                        vote = site.xpath('.//i')[0].text
                        comments = site.xpath('.//i')[1].text
                    except:
                        pass
                    result = {
                        'imgUrl': imgUrl,
                        'title': title,
                        'content': content,
                        'vote': vote,
                        'comments': comments,
                    }

                    with self.lock:
                        # print 'write %s' % json.dumps(result)
                        self.f.write(json.dumps(result, ensure_ascii=False).encode('utf-8') + "\n")

                except Exception, e:
                    print 'site in result', e
        except Exception, e:
            print 'parse_data', e
        with self.lock:
            total += 1

data_queue = Queue()
exitFlag_Parser = False
lock = threading.Lock()
total = 0

def main():
    output = open('qiushibaike.json', 'a')

    #初始化網頁頁碼page從1-10個頁面
    pageQueue = Queue(50)
    for page in range(1, 11):
        pageQueue.put(page)

    #初始化採集執行緒
    crawlthreads = []
    crawlList = ["crawl-1", "crawl-2", "crawl-3"]

    for threadID in crawlList:
        thread = thread_crawl(threadID, pageQueue)
        thread.start()
        crawlthreads.append(thread)

    #初始化解析執行緒parserList
    parserthreads = []
    parserList = ["parser-1", "parser-2", "parser-3"]
    #分別啟動parserList
    for threadID in parserList:
        thread = Thread_Parser(threadID, data_queue, lock, output)
        thread.start()
        parserthreads.append(thread)

    # 等待佇列清空
    while not pageQueue.empty():
        pass

    # 等待所有執行緒完成
    for t in crawlthreads:
        t.join()

    while not data_queue.empty():
        pass
    # 通知執行緒是時候退出
    global exitFlag_Parser
    exitFlag_Parser = True

    for t in parserthreads:
        t.join()
    print "Exiting Main Thread"
    with lock:
        output.close()


if __name__ == '__main__':
    main()