多執行緒糗事百科案例

案例要求參考上一個糗事百科單程序案例

Queue（佇列物件）

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()