Linux环境下 多线程下载 (Python 实现版)

本文是多年前学习编程时参照一个网友程序的基础之上改写的， 采用Python语音编写， 多线程下载功能， 可以有效提高Linux下原有下载工具中的一些不足，以下给出具体代码。

#!/usr/bin/python
# -*- coding: utf-8 -*-
# Author: Devilmaycry
# Email: 812839668@qq.com
# 本程序是多年前参照他人代码所写，并在原基础上做了一定改进，因时间过久已无法给出原出处，特此声明
# 测试平台 Ubuntu 14.04 X86_64 Python 2.7.6

import threading
import urllib2
import sys
import time

# 全局最大线程数
max_thread = 20 

# 初始化锁
lock = threading.RLock()

class Downloader(threading.Thread):
    def __init__(self, url, start_size, end_size, fobj, buffer):
        self.url = url
        self.buffer = buffer
        self.start_size = start_size
        self.end_size = end_size
        self.fobj = fobj
        threading.Thread.__init__(self)

        #重连接次数
        self.i = 1

    def run(self):
        print 'starting: %s' % self.getName()
        self._download()

    def _download(self):
        while True:
            try:
                offset = self.start_size  

                req = urllib2.Request(self.url)

                # 添加HTTP Header(RANGE)设置下载数据的范围
                req.headers['Range'] = 'bytes=%s-%s' % (self.start_size, self.end_size)

                f = urllib2.urlopen(req, timeout = 15)

                # 初始化当前线程文件对象偏移量
                while 1:
                    block = f.read(self.buffer)  
                    
                    # 当前线程数据获取完毕后, 则退出
                    if not block:
                        print '%s done.' % self.getName()
                        break

                    with lock: 
                        # 设置文件对象偏移地址
                        self.fobj.seek(offset)

                        # 写入获取到的数据
                        self.fobj.write(block)

                    offset = offset + len(block)
                break
            except Exception:
                print self.getName() + " failed time " + "====="*10 + str(self.i) + "
"
                self.i = self.i + 1
                self.start_size = offset 


def main(url, threadNum=30, save_file='', buffer=1024):
    # 最大线程数量不能超过max_thread
    threadNum = threadNum if threadNum <= max_thread else max_thread

    # 获取文件的大小
    req = urllib2.urlopen(url)
    size = int(req.info().getheaders('Content-Length')[0])

    # 初始化文件对象
    fobj = open(save_file, 'wb')

    # 根据线程数量计算 每个线程负责的http Range 大小
    avg_size, pad_size = divmod(size, threadNum)

    plist = []

    for i in xrange(threadNum):
        start_size = i*avg_size
        end_size = start_size + avg_size - 1

        if i == threadNum - 1:
            # 最后一个线程加上pad_size
            end_size = end_size + pad_size + 1

        pTemp = Downloader(url, start_size, end_size, fobj, buffer)

        plist.append(pTemp)

    #  开始搬砖
    for t in plist:
        t.start()

    # 等待所有线程结束
    for t in plist:
        t.join()

    # 结束当然记得关闭文件对象
    fobj.close()
    print 'Download completed!'


if __name__ == '__main__':
    start = time.time()

    #url = "http://dlsw.baidu.com/sw-search-sp/soft/3a/12350/QQ7.1.14509.0.1429585990.exe"
    url="https://d3kbcqa49mib13.cloudfront.net/spark-2.1.1-bin-hadoop2.7.tgz"

    main(url=url, threadNum=20, save_file='test', buffer=4096)

    end = time.time()

    print end-start