如何在python中使用多线程时获得更快的速度

Question

现在我正在研究如何尽快从网站上获取数据.为了获得更快的速度,我考虑使用多线程.这是我用来测试多线程和简单帖子之间差异的代码.

import threading
import time
import urllib
import urllib2


class Post:

    def __init__(self, website, data, mode):
        self.website = website
        self.data = data

        #mode is either "Simple"(Simple POST) or "Multiple"(Multi-thread POST)
        self.mode = mode

    def post(self):

        #post data
        req = urllib2.Request(self.website)
        open_url = urllib2.urlopen(req, self.data)

        if self.mode == "Multiple":
            time.sleep(0.001)

        #read HTMLData
        HTMLData = open_url.read()



        print "OK"

if __name__ == "__main__":

    current_post = Post("http://forum.xda-developers.com/login.php", "vb_login_username=test&vb_login_password&securitytoken=guest&do=login", \
                        "Simple")

    #save the time before post data
    origin_time = time.time()

    if(current_post.mode == "Multiple"):

        #multithreading POST

        for i in range(0, 10):
           thread = threading.Thread(target = current_post.post)
           thread.start()
           thread.join()

        #calculate the time interval
        time_interval = time.time() - origin_time

        print time_interval

    if(current_post.mode == "Simple"):

        #simple POST

        for i in range(0, 10):
            current_post.post()

        #calculate the time interval
        time_interval = time.time() - origin_time

        print time_interval

正如您所看到的,这是一个非常简单的代码.首先我将模式设置为"简单",我可以得到时间间隔:50秒(也许我的速度有点慢:().然后我将模式设置为"多个",我得到时间间隔:35.从我可以看出,多线程实际上可以提高速度,但结果并不像我想象的那样好.我希望得到更快的速度.

从调试开始,我发现该程序主要阻塞在以下行:open_url = urllib2.urlopen(req, self.data)这行代码需要花费大量时间来发布和接收来自指定网站的数据.我想也许我可以通过time.sleep()在urlopen函数内部添加和使用多线程来获得更快的速度,但我不能这样做,因为它是python自己的函数.

如果不考虑服务器阻止后期速度的可能限制,我还能做些什么才能获得更快的速度？或者我可以修改的任何其他代码？多谢!

Answer 1

你做错的最重要的事情就是你打电话的方式thread.start()和thread.join():

for i in range(0, 10):
   thread = threading.Thread(target = current_post.post)
   thread.start()
   thread.join()

每次循环,你创建一个线程,启动它,然后等待它完成继续前进到下一个线程.你根本没有做任何事情!

你可能应该做的是:

threads = []

# start all of the threads
for i in range(0, 10):
   thread = threading.Thread(target = current_post.post)
   thread.start()
   threads.append(thread)

# now wait for them all to finish
for thread in threads:
   thread.join()

Answer 2

在许多情况下,python的线程并不能很好地提高执行速度......有时,它会使情况变得更糟.有关更多信息,请参阅David Beazley关于Global Interpreter Lock/Pycon2010 GIL幻灯片的PyCon2010演示文稿.这个演示文稿内容丰富,我强烈推荐给任何考虑线程的人...

尽管David Beazley的演讲解释了网络流量改进了Python线程模块的调度,但您应该使用多处理模块.我在您的代码中包含了这个选项(请参阅我的答案底部).

在我的一台旧机器上运行它(Python 2.6.6):

current_post.mode == "Process"  (multiprocessing)  --> 0.2609 seconds
current_post.mode == "Multiple" (threading)        --> 0.3947 seconds
current_post.mode == "Simple"   (serial execution) --> 1.650 seconds

我同意TokenMacGuy的评论,上面的数字包括转移.join()到另一个循环.如您所见,python的多处理速度明显快于线程.

from multiprocessing import Process
import threading
import time
import urllib
import urllib2


class Post:

    def __init__(self, website, data, mode):
        self.website = website
        self.data = data

        #mode is either:
        #   "Simple"      (Simple POST)
        #   "Multiple"    (Multi-thread POST)
        #   "Process"     (Multiprocessing)
        self.mode = mode
        self.run_job()

    def post(self):

        #post data
        req = urllib2.Request(self.website)
        open_url = urllib2.urlopen(req, self.data)

        if self.mode == "Multiple":
            time.sleep(0.001)

        #read HTMLData
        HTMLData = open_url.read()

        #print "OK"

    def run_job(self):
        """This was refactored from the OP's code"""
        origin_time = time.time()
        if(self.mode == "Multiple"):

            #multithreading POST
            threads = list()
            for i in range(0, 10):
               thread = threading.Thread(target = self.post)
               thread.start()
               threads.append(thread)
            for thread in threads:
               thread.join()
            #calculate the time interval
            time_interval = time.time() - origin_time
            print "mode - {0}: {1}".format(method, time_interval)

        if(self.mode == "Process"):

            #multiprocessing POST
            processes = list()
            for i in range(0, 10):
               process = Process(target=self.post)
               process.start()
               processes.append(process)
            for process in processes:
               process.join()
            #calculate the time interval
            time_interval = time.time() - origin_time
            print "mode - {0}: {1}".format(method, time_interval)

        if(self.mode == "Simple"):

            #simple POST
            for i in range(0, 10):
                self.post()
            #calculate the time interval
            time_interval = time.time() - origin_time
            print "mode - {0}: {1}".format(method, time_interval)
        return time_interval

if __name__ == "__main__":

    for method in ["Process", "Multiple", "Simple"]:
        Post("http://forum.xda-developers.com/login.php", 
            "vb_login_username=test&vb_login_password&securitytoken=guest&do=login",
            method
            )