python多线程抓取图片效率对比

目的:

是学习python 多线程的工作原理,及通过抓取400张图片这种io密集型应用来查看多线程效率对比

import requests
import urlparse
import os
import time
import threading
import queue
path = ‘/home/lidongwei/scrapy/owan_img_urls.txt’
#path = ‘/home/lidongwei/scrapy/cc.txt’
fetch_img_save_path = ‘/home/lidongwei/scrapy/owan_imgs/’
# 读取保存再文件里面400个urls
with open(path) as f :
urls = f.readlines()
urls = urls[:400]
# 使用queue来线程通信,因为队列是线程安全的(就是默认这个队列已经有锁)
q = queue.queue()
for url in urls:
q.put(url)
start = time.time()
def fetch_img_func(q):
while true:
try:
# 不阻塞的读取队列数据
url = q.get_nowait()
i = q.qsize()
except exception, e:
print e
break;
print ‘current thread name runing %s … 11’ % threading.currentthread().name
url = url.strip()
img_path = urlparse.urlparse(url).path
ext = os.path.splitext(img_path)[1]
print ‘handle %s pic… pic url %s ‘ % (i, url)
res = requests.get(url, stream=true)
if res.status_code == 200:
save_img_path = ‘%s%s%s’ % (fetch_img_save_path, i, ext)
# 保存下载的图片
with open(save_img_path, ‘wb’) as fs:
for chunk in res.iter_content(1024):
fs.write(chunk)
print ‘save %s pic ‘ % i
# 可以开多个线程测试不同效果
t1 = threading.thread(target=fetch_img_func, args=(q, ), name=”child_thread_1″)
#t2 = threading.thread(target=fetch_img_func, args=(q, ), name=”child_thread_2″)
#t3 = threading.thread(target=fetch_img_func, args=(q, ), name=”child_thread_3″)
#t4 = threading.thread(target=fetch_img_func, args=(q, ), name=”child_thread_4″)
t1.start()
#t2.start()
#t3.start()
#t4.start()
t1.join()
#t2.join()
#t3.join()
#t4.join()
end = time.time()
print ‘done %s ‘ % (end-start)

实验结果

400图片

4线程 done 12.443133831
3线程 done 12.9201757908
2线程 done 32.8628299236
1线程 done 54.6115460396

总结

python 自带gil 大锁, 没有真正意义上的多线程并行执行。gil 大锁会在线程阻塞的时候释放,此时等待的线程就可以激活工作,这样如此类推,大大提高io阻塞型应用的效率。