python multi-process programming often use several methods to

Multithreading in python is not really true multi-threaded, if you want to get the most from multicore CPU resources, in most cases require the use of multiple processes in python. python provides a very easy to use multi-process packages Multiprocessing, only need to define a function, python does all the other things. With this package, you can easily complete the conversion from single-process to be executed concurrently. multiprocessing support the child, communicate and share data and synchronize different forms, provides Process, Queue, Pipe, LocK and other components

A, Process

语法：Process([group[,target[,name[,args[,kwargs]]]]])

Definition: target represents the calling object; args parameter indicates the position of the ancestral calling object; kwargs represent the calling object dictionary. name as an alias, groups will not actually called.

Methods: is_alive ():

　　　join(timeout)：

　　　run()：

　　　start()：

　　　terminate()：

Properties: authkey, daemon (through start () is provided), exitcode (process runtime None, if -N, representing the end signal N), name, pid. Where the daemon is automatically terminated after the termination of the parent process, and they can not generate a new process must be set before the start ().

1. Create a function, and as a single process

from multiprocessing import Process
def func(name):
    print("%s曾经是好人"%name)

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    p.start()   #start()通知系统开启这个进程

2. Create a function and as more processes

from multiprocessing import Process
import random,time

def hobby_motion(name):
    print('%s喜欢运动'% name)
    time.sleep(random.randint(1,3))

def hobby_game(name):
    print('%s喜欢游戏'% name)
    time.sleep(random.randint(1,3))

if __name__ == "__main__":
    p1 = Process(target=hobby_motion,args=('付婷婷',))
    p2 = Process(target=hobby_game,args=('科比',))
    p1.start()
    p2.start()

Results of the:

付婷婷喜欢运动
科比喜欢游戏

3. The process defined as a class (Another way to start a process, not very common)

from multiprocessing import Process
class MyProcess(Process):
    def __init__(self,name):
        super().__init__()
        self.name = name

    def run(self):  #start()时，run自动调用，而且此处只能定义为run。
        print("%s曾经是好人"%self.name)

if __name__ == "__main__":
    p = MyProcess('kebi')
    p.start()  #将Process当作父类，并且自定义一个函数。

4.daemon program contrast effect

Without daemon property

import time
def func(name):
    print("work start:%s"% time.ctime())
    time.sleep(2)
    print("work end:%s"% time.ctime())

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    p.start()
    print("this is over")

#执行结果
this is over
work start:Thu Nov 30 16:12:00 2017
work end:Thu Nov 30 16:12:02 2017

Plus daemon property

from multiprocessing import Process
import time
def func(name):
    print("work start:%s"% time.ctime())
    time.sleep(2)
    print("work end:%s"% time.ctime())

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    p.daemon = True   #父进程终止后自动终止，不能产生新进程，必须在start()之前设置
    p.start()
    print("this is over")

#执行结果
this is over

Set the method of executing the daemon attribute want:

import time
def func(name):
    print("work start:%s"% time.ctime())
    time.sleep(2)
    print("work end:%s"% time.ctime())

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    p.daemon = True
    p.start()
    p.join()  #执行完前面的代码再执行后面的
    print("this is over")

#执行结果
work start:Thu Nov 30 16:18:39 2017
work end:Thu Nov 30 16:18:41 2017
this is over

5.join (): After the above code is completed before execution code of the i-th surface.

Look at an example:

from multiprocessing import Process
import time,os,random
def func(name,hour):
    print("A lifelong friend:%s,%s"% (name,os.getpid()))
    time.sleep(hour)
    print("Good bother:%s"%name)

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',2))
    p1 = Process(target=func,args=('maoxian',1))
    p2 = Process(target=func,args=('xiaoniao',3))
    p.start()
    p1.start()
    p2.start()
    print("this is over")

Results of the:

this is over   #最后执行，最先打印，说明start()只是开启进程，并不是说一定要执行完
A lifelong friend:kebi,12048
A lifelong friend:maoxian,8252
A lifelong friend:xiaoniao,6068
Good bother:maoxian   #最先打印，第二位执行
Good bother:kebi     
Good bother:xiaoniao

Add join ()

from multiprocessing import Process
import time,os,random
def func(name,hour):
    print("A lifelong friend:%s,%s"% (name,os.getpid()))
    time.sleep(hour)
    print("Good bother:%s"%name)
start = time.time()
if __name__ == "__main__":
    p = Process(target=func,args=('kebi',2))
    p1 = Process(target=func,args=('maoxian',1))
    p2 = Process(target=func,args=('xiaoniao',3))
    p.start()
    p.join()   #上面的代码执行完毕之后，再执行后面的
    p1.start()
    p1.join()
    p2.start()
    p2.join()
    print("this is over")
    print(time.time() - start)

#执行结果
A lifelong friend:kebi,14804
Good bother:kebi
A lifelong friend:maoxian,11120
Good bother:maoxian
A lifelong friend:xiaoniao,10252  #每个进程执行完了，才会执行下一个
Good bother:xiaoniao
this is over
6.497815370559692   #2+1+3+主程序执行时间

A change of position

from multiprocessing import Process
import time,os,random
def func(name,hour):
    print("A lifelong friend:%s,%s"% (name,os.getpid()))
    time.sleep(hour)
    print("Good bother:%s"%name)
start = time.time()
if __name__ == "__main__":
    p = Process(target=func,args=('kebi',2))
    p1 = Process(target=func,args=('maoxian',1))
    p2 = Process(target=func,args=('xiaoniao',3))
    p.start()
    p1.start()
    p2.start()
    p.join()   #需要2秒
    p1.join()  #到这时已经执行完
    p2.join()   #已经执行了2秒，还要1秒
    print("this is over")
    print(time.time() - start)

#执行结果

A lifelong friend:kebi,13520
A lifelong friend:maoxian,11612
A lifelong friend:xiaoniao,17064  #几乎是同时开启执行
Good bother:maoxian
Good bother:kebi
Good bother:xiaoniao
this is over
3.273620367050171  #以最长时间的为主

6. Other Properties and Methods

from multiprocessing import Process
import time
def func(name):
    print("work start:%s"% time.ctime())
    time.sleep(2)
    print("work end:%s"% time.ctime())

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    p.start()
    p.terminate()  #将进程杀死，而且必须放在start()后面，与daemon的功能类似

#执行结果
this is over

from multiprocessing import Process
import time
def func(name):
    print("work start:%s"% time.ctime())
    time.sleep(2)
    print("work end:%s"% time.ctime())

if __name__ == "__main__":
    p = Process(target=func,args=('kebi',))
    # p.daemon = True
    print(p.is_alive())
    p.start()
    print(p.name)   #获取进程的名字
    print(p.pid)    #获取进程的pid
    print(p.is_alive())  #判断进程是否存在
    print("this is over")