本文实例讲述了Python3多进程 multiprocessing 模块。分享给大家供大家参考，具体如下：

多进程 Multiprocessing 模块

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multiprocessing 模块官方说明文档

Process 类

Process 类用来描述一个进程对象。创建子进程的时候，只需要传入一个执行函数和函数的参数即可完成 Process 示例的创建。

star()方法启动进程，

join()方法实现进程间的同步，等待所有进程退出。

close() 用来阻止多余的进程涌入进程池 Pool 造成进程阻塞。

multiprocessing.Process(group=None, target=None, name=None, args=(), kwargs={}, *, daemon=None)

target是函数名字，需要调用的函数

args函数需要的参数，以 tuple 的形式传入

示例：

import multiprocessing

import os

def run_proc(name):

print('Child process {0} {1} Running '.format(name, os.getpid()))

if __name__ == '__main__':

print('Parent process {0} is Running'.format(os.getpid()))

for i in range(5):

p = multiprocessing.Process(target=run_proc, args=(str(i),))

print('process start')

p.start()

p.join()

print('Process close')

结果：

Parent process 809 is Running

process start

process start

process start

process start

process start

Child process 0 810 Running

Child process 1 811 Running

Child process 2 812 Running

Child process 3 813 Running

Child process 4 814 Running

Process close

Pool

Pool 可以提供指定数量的进程供用户使用，默认是 CPU 核数。当有新的请求提交到 Poll 的时候，如果池子没有满，会创建一个进程来执行，否则就会让该请求等待。

- Pool 对象调用 join 方法会等待所有的子进程执行完毕

- 调用 join 方法之前，必须调用 close

- 调用 close 之后就不能继续添加新的 Process 了

pool.apply_async

apply_async方法用来同步执行进程，允许多个进程同时进入池子。

import multiprocessing

import os

import time

def run_task(name):

print('Task {0} pid {1} is running, parent id is {2}'.format(name, os.getpid(), os.getppid()))

time.sleep(1)

print('Task {0} end.'.format(name))

if __name__ == '__main__':

print('current process {0}'.format(os.getpid()))

p = multiprocessing.Pool(processes=3)

for i in range(6):

p.apply_async(run_task, args=(i,))

print('Waiting for all subprocesses done...')

p.close()

p.join()

print('All processes done!')

结果：

current process 921

Waiting for all subprocesses done...

Task 0 pid 922 is running, parent id is 921

Task 1 pid 923 is running, parent id is 921

Task 2 pid 924 is running, parent id is 921

Task 0 end.

Task 3 pid 922 is running, parent id is 921

Task 1 end.

Task 4 pid 923 is running, parent id is 921

Task 2 end.

Task 5 pid 924 is running, parent id is 921

Task 3 end.

Task 4 end.

Task 5 end.

All processes done!

pool.apply

apply(func[, args[, kwds]])

该方法只能允许一个进程进入池子，在一个进程结束之后，另外一个进程才可以进入池子。

import multiprocessing

import os

import time

def run_task(name):

print('Task {0} pid {1} is running, parent id is {2}'.format(name, os.getpid(), os.getppid()))

time.sleep(1)

print('Task {0} end.'.format(name))

if __name__ == '__main__':

print('current process {0}'.format(os.getpid()))

p = multiprocessing.Pool(processes=3)

for i in range(6):

p.apply(run_task, args=(i,))

print('Waiting for all subprocesses done...')

p.close()

p.join()

print('All processes done!')

结果：

Task 0 pid 928 is running, parent id is 927

Task 0 end.

Task 1 pid 929 is running, parent id is 927

Task 1 end.

Task 2 pid 930 is running, parent id is 927

Task 2 end.

Task 3 pid 928 is running, parent id is 927

Task 3 end.

Task 4 pid 929 is running, parent id is 927

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