详解python之多进程和进程池(Processing库)

环境:win7+python2.7

一直想学习多进程或多线程,但之前只是单纯看一点基础知识还有简单的介绍,无法理解怎么去应用,直到前段时间看了github的一个爬虫项目涉及到多进程,多线程相关内容,一边看一边百度相关知识点,现在把一些相关知识点和一些应用写下来做个记录.

首先说下什么是进程:进程是程序在计算机上的一次执行活动,当运行一个程序的时候,就启动了一个进程.而进程又分为系统进程和用户进程.只要是用于完成操作系统的各种功能的进程就是系统进程,它们就是处于运行状态下的操作系统本身;而所有由你启动的进程都是用户进程。进程是操作系统进行资源分配的单位。

直观点说,在任务管理器的用户名上标明system的是系统进程,标明administrator的是用户进程,另外net是网洛,lcacal service是本地服务,关于进程更加具体的信息可以百科,这里得省点力气,不然收不回了.

一.多进程的简单使用

如图,multiprocessing有多个函数,很多我也还没去了解,这里只讲我目前了解的.

进程创建:Process(target=主要运行的函数,name=自定义进程名称可不写,args=(参数))

方法：

1. is_alive():判断进程是否存活
2. join([timeout]):子进程结束再执行下一步,timeout为超时时间,有时进程遇到阻塞,为了程序能够运行下去而设置超时时间
3. run():如果在创建Process对象的时候不指定target，那么就会默认执行Process的run方法
4. start():启动进程,区分run()
5. terminate():终止进程,关于终止进程没有这么简单,貌似用psutil包会更好,有机会以后了解更多再写下。
   

其中，Process以start()启动某个进程。

属性：

1. authkey: 在文档中authkey()函数找到这么一句话:Set authorization key of process设置过程的授权密钥 ,目前没找到相关应用实例,这个密钥是怎么用的呢"htmlcode">

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    p1=Process(target=fun1,args=(4,))
    p2 = Process(target=fun2, args=(6,))
    p1.start()
    p2.start()
    p1.join()
    p2.join()
    b=time.time()
    print 'finish',b-a
   
   

   这里一共开了两个进程,p1和p2,arg=(4,)中的4是fun1函数的参数,这里要用tulpe类型,如果两个参数或更多就是arg=(参数1,参数2...),之后用start()启动进程,我们设置等待p1和p2进程结束再执行下一步.来看下面的运行结果,fun2和fun1基本在同一时间开始运行,当运行完毕(fun1睡眠4秒,同时fun2睡眠6秒),才执行print 'finish',b-a语句

   this is fun2 Mon Jun 05 13:48:04 2017
   this is fun1 Mon Jun 05 13:48:04 2017
   fun1 finish Mon Jun 05 13:48:08 2017
   fun2 finish Mon Jun 05 13:48:10 2017
   finish 6.20300006866
   
   Process finished with exit code 0
   

   我们再来看下start()与join()处于不同位置会发生什么

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    p1=Process(target=fun1,args=(4,))
    p2 = Process(target=fun2, args=(6,))
    p1.start()
    p1.join()
    p2.start()
    p2.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun1 Mon Jun 05 14:19:28 2017
   fun1 finish Mon Jun 05 14:19:32 2017
   this is fun2 Mon Jun 05 14:19:32 2017
   fun2 finish Mon Jun 05 14:19:38 2017
   finish 10.1229999065
   
   Process finished with exit code 0
   

   看,现在是先运行fun1函数,运行完毕再运行fun2接着再是print 'finish',即先运行进程p1再运行进程p2,感受到join()的魅力了吧.现在再试试注释掉join()看看又会出现什么

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    p1=Process(target=fun1,args=(4,))
    p2 = Process(target=fun2, args=(6,))
    p1.start()
    p2.start()
    p1.join()
    #p2.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun1 Mon Jun 05 14:23:57 2017
   this is fun2 Mon Jun 05 14:23:58 2017
   fun1 finish Mon Jun 05 14:24:01 2017
   finish 4.05900001526
   fun2 finish Mon Jun 05 14:24:04 2017
   
   Process finished with exit code 0
   

   这次是运行完fun1(因为p1进程有用join(),所以主程序等待p1运行完接着执行下一步),接着继续运行主进程的print 'finish',最后fun2运行完毕才结束
   

   2.name,daemon,is_alive():

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    p1=Process(name='fun1进程',target=fun1,args=(4,))
    p2 = Process(name='fun2进程',target=fun2, args=(6,))
    p1.daemon=True
    p2.daemon = True
    p1.start()
    p2.start()
    p1.join()
    print p1,p2
    print '进程1:',p1.is_alive(),'进程2:',p2.is_alive()
    #p2.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun2 Mon Jun 05 14:43:49 2017
   this is fun1 Mon Jun 05 14:43:49 2017
   fun1 finish Mon Jun 05 14:43:53 2017
   <Process(fun1进程, stopped daemon)> <Process(fun2进程, started daemon)>
   进程1: False 进程2: True
   finish 4.06500005722
   
   Process finished with exit code 0
   

   可以看到,name是给进程赋予名字, 运行到print '进程1:',p1.is_alive(),'进程2:',p2.is_alive() 这句的时候,p1进程已经结束(返回False),p2进程仍然在运行(返回True),但p2没有用join(),所以直接接着执行主进程,由于用了daemon=Ture,父进程终止后自动终止,p2进程没有结束就强行结束整个程序了.

   3.run()

   run()在Process没有指定target函数时,默认用run()函数运行程序,

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a = time.time()
    p=Process()
    p.start()
    p.join()
    b = time.time()
    print 'finish', b - a
   
   

   结果:

   finish 0.0840001106262

   从结果看出,进程p什么也没做,为了让进程正常运行,我们酱紫写:
   

   目标函数没有参数:

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1():
    print 'this is fun1',time.ctime()
    time.sleep(2)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a = time.time()
    p=Process()
    p.run=fun1
    p.start()
    p.join()
    b = time.time()
    print 'finish', b - a
   
   

   结果:

   this is fun1 Mon Jun 05 16:34:41 2017
   fun1 finish Mon Jun 05 16:34:43 2017
   finish 2.11500000954
   
   Process finished with exit code 0
   

   目标函数有参数:

   # -*- coding:utf-8 -*-
   from multiprocessing import Process
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a = time.time()
    p=Process()
    p.run=fun1(2)
    p.start()
    p.join()
    b = time.time()
    print 'finish', b - a
   
   

   结果:

   this is fun1 Mon Jun 05 16:36:27 2017
   fun1 finish Mon Jun 05 16:36:29 2017
   Process Process-1:
   Traceback (most recent call last):
    File "E:\Anaconda2\lib\multiprocessing\process.py", line 258, in _bootstrap
    self.run()
   TypeError: 'NoneType' object is not callable
   finish 2.0529999733
   
   Process finished with exit code 0
   

   目标函数有参数的出现了异常,为什么呢"htmlcode">

   # -*- coding:utf-8 -*-
   from multiprocessing import Pool
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    pool = Pool(processes =3) # 可以同时跑3个进程
    for i in range(3,8):
     pool.apply_async(fun1,(i,))
    pool.close()
    pool.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun1 Mon Jun 05 15:15:38 2017
   this is fun1 Mon Jun 05 15:15:38 2017
   this is fun1 Mon Jun 05 15:15:38 2017
   fun1 finish Mon Jun 05 15:15:41 2017
   this is fun1 Mon Jun 05 15:15:41 2017
   fun1 finish Mon Jun 05 15:15:42 2017
   this is fun1 Mon Jun 05 15:15:42 2017
   fun1 finish Mon Jun 05 15:15:43 2017
   fun1 finish Mon Jun 05 15:15:47 2017
   fun1 finish Mon Jun 05 15:15:49 2017
   finish 11.1370000839
   
   Process finished with exit code 0
   

   从上面的结果可以看到,设置了3个运行进程上限,15:15:38这个时间同时开始三个进程,当第一个进程结束时(参数为3秒那个进程),会添加新的进程,如此循环,直至进程池运行完再执行主进程语句b=time.time() print 'finish',b-a .这里用到非阻塞apply_async(),再来对比下阻塞apply()

   # -*- coding:utf-8 -*-
   from multiprocessing import Pool
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    pool = Pool(processes =3) # 可以同时跑3个进程
    for i in range(3,8):
     pool.apply(fun1,(i,))
    pool.close()
    pool.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun1 Mon Jun 05 15:59:26 2017
   fun1 finish Mon Jun 05 15:59:29 2017
   this is fun1 Mon Jun 05 15:59:29 2017
   fun1 finish Mon Jun 05 15:59:33 2017
   this is fun1 Mon Jun 05 15:59:33 2017
   fun1 finish Mon Jun 05 15:59:38 2017
   this is fun1 Mon Jun 05 15:59:38 2017
   fun1 finish Mon Jun 05 15:59:44 2017
   this is fun1 Mon Jun 05 15:59:44 2017
   fun1 finish Mon Jun 05 15:59:51 2017
   finish 25.1610000134
   
   Process finished with exit code 0
   
   

   可以看到,阻塞是当一个进程结束后,再进行下一个进程,一般我们都用非阻塞apply_async()

   2.多个进程池

   上面是使用单个进程池的,对于多个进程池,我们可以用for循环,直接看代码

   # -*- coding:utf-8 -*-
   from multiprocessing import Pool
   import time
   
   def fun1(t):
    print 'this is fun1',time.ctime()
    time.sleep(t)
    print 'fun1 finish',time.ctime()
   
   def fun2(t):
    print 'this is fun2',time.ctime()
    time.sleep(t)
    print 'fun2 finish',time.ctime()
   
   if __name__ == '__main__':
    a=time.time()
    pool = Pool(processes =3) # 可以同时跑3个进程
    for fun in [fun1,fun2]:
     for i in range(3,8):
      pool.apply_async(fun,(i,))
    pool.close()
    pool.join()
    b=time.time()
    print 'finish',b-a
   
   

   结果:

   this is fun1 Mon Jun 05 16:04:38 2017
   this is fun1 Mon Jun 05 16:04:38 2017
   this is fun1 Mon Jun 05 16:04:38 2017
   fun1 finish Mon Jun 05 16:04:41 2017
   this is fun1 Mon Jun 05 16:04:41 2017
   fun1 finish Mon Jun 05 16:04:42 2017
   this is fun1 Mon Jun 05 16:04:42 2017
   fun1 finish Mon Jun 05 16:04:43 2017
   this is fun2 Mon Jun 05 16:04:43 2017
   fun2 finish Mon Jun 05 16:04:46 2017
   this is fun2 Mon Jun 05 16:04:46 2017
   fun1 finish Mon Jun 05 16:04:47 2017
   this is fun2 Mon Jun 05 16:04:47 2017
   fun1 finish Mon Jun 05 16:04:49 2017
   this is fun2 Mon Jun 05 16:04:49 2017
   fun2 finish Mon Jun 05 16:04:50 2017
   this is fun2 Mon Jun 05 16:04:50 2017
   fun2 finish Mon Jun 05 16:04:52 2017
   fun2 finish Mon Jun 05 16:04:55 2017
   fun2 finish Mon Jun 05 16:04:57 2017
   finish 19.1670000553
   
   Process finished with exit code 0
   
   

   看到了,在fun1运行完接着运行fun2.

   另外对于没有参数的情况,就直接 pool.apply_async(funtion),无需写上参数.

   在学习编写程序过程,曾遇到不用if _name_ == '_main_':而直接运行程序,这样结果会出错,经查询,在Windows上要想使用进程模块，就必须把有关进程的代码写在当前.py文件的if _name_ == ‘_main_' :语句的下面，才能正常使用Windows下的进程模块。Unix/Linux下则不需要。原因有人这么说:在执行的時候，由于你写的 py 会被当成module 读进执行。所以，一定要判断自身是否为 _main_。也就是要：

   if __name__ == ‘__main__' :
   # do something.

   这里我自己还搞不清楚,期待以后能够理解

   学习的过程中,还涉及了经常和进程一起运用的队列Queue和线程threading,有时间以后再写吧，希望对大家的学习有所帮助，也希望大家多多支持。