python-10多进程

1-多进程（multiprocessing）， 1个父进程可以有多少子进程

1.1下面的例子演示了启动一个子进程并等待其结束

from multiprocessing import Process
import os

def run_proc(name):
    print('Run child process %s (%s)' % (name,os.getpid())) #父进程的ID

if __name__ =='__main__':
    print('Parent process %s. ' % os.getpid())
    p = Process(target=run_proc, args=('test', ))
    print('Child process will start')
    p.start() #开始进程
    p.join() #待子子进程结束
    print('Child process end')

1.2 pool

　　　　如果要启动大量的子进程，可以用进程池的方式批量创建子进程：

from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print("Run task %s (%s)" % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random()*3)
    end = time.time()
    print("Task %s runs %0.2f seconds" % (name, (end - start)))

if __name__ =='__main__':
    print('Parent process %s' % os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print("Waiting for all subprocesses done...")
    p.close()
    p.join(); #调用join()之前必须先调用close()，调用close()之后就不能继续添加新的Process了。
    print("All subprocesses done.")

1.3子进程

import subprocess
print("$ nslookup www.python.org")
r = subprocess.call(['nslookup','www.python.org'])
print("exit code:", r)

1.4进程间通讯

Python的multiprocessing模块包装了底层的机制，提供了Queue、Pipes等多种方式来交换数据。

from multiprocessing import Process,Queue
import os, time, random
def write(q):
    print('Process to write:%s' % os.getpid())
    for value in ['A','B','C']:
        print('Put %s to queue...' % value)
        q.put(value) #写入数据
        time.sleep(random.random())

def read(q):
    print('Process to read: %s' % os.getpid())
    while True:
        value = q.get(True) #等待写入
        print('Get %s from queue.' % value)

if __name__ == '__main__':
    q = Queue()
    pw = Process(target=write, args=(q,))
    pr = Process(target=read, args=(q,))
    pw.start() #开始写
    pr.start()  #开始读
    pw.join() #等等pw结束
    pr.terminate() #由于是死循环，强制终止程序