python中的多進程運用

1. 程序中另起進程

from multiprocessing import Process
from os import getpid
from time import sleep

def run_time(name):
    sleep(5)
    print('child progress {}: {}'.format(name, getpid()))

if __name__ == '__main__':
    print('parent progress id: {}'.format(getppid()))  # os.getpid(): 獲取當前進程ID; os.getppid(): 獲取父進程ID
    p = Process(target=run_time, args=('hello_world',))  # 初始化子進程：target=目前函數名， args=參數
    print('start child progress')
    p.start()  # 啓動子進程
    p.join()  # 進程同步：等待子進程執行完畢，程序再向下執行
    print('end child progress')

方法

• getppid()、getpid()
• p.start()
• p.join()
• Process(target=, args=(,))
• Pool(n)
• p.apply_async(, args=(,))
• subprocess.call([’’, ‘’])
• Queue()
• q.put(value)
• q.get(True)

2. 進程池

from multiprocessing import Pool
from os import getpid
from time import sleep

def long_time_task(name):
    sleep(5)
    print('child process {0}: {1}\n'.format(name, getpid()))

if __name__ == '__main__':
    print('parent process: {0}\n'.format(getpid()))
    p = Pool(2)  ## 初始化進程池：一次可並行執行2個進程（等這兩個執行結束，再次啓動執行接下來的兩個，和電腦是幾核的無關）

    for i in range(10):
        p.apply_async(long_time_task, args=(i,))  ## 進程池添加進程
    print('start child progress\n')
    p.close()  ## 關閉進程池（不能再添加新進程了），準備執行進程
    p.join()  # 進程同步
    print('end child progress\n')

3. 問題：無法獲取子進程的執行結果 -> 子進程

import subprocess

print('nslookup www.python.org')
r = subprocess.call(['nslookup', 'www.python.org'])
print('Exit code: {}'.format(r))

4. 進程間通信

• 隊列：Queue

from multiprocessing import Process, Queue
from time import sleep
from random import random

def write(q):
    for i in range(5):
        print('puts {}'.format(i))
        q.put(i)
        sleep(1)

def read(q):
    sleep(10)
    while True:
        i = q.get(True)
        print('get {}'.format(i))

if __name__ == '__main__':
    q = Queue()
    pw = Process(target=write, args=(q,))
    pr = Process(target=read, args=(q,))
    print('START')
    pw.start()
    pr.start()
    pw.join()
    while True:
        if q.empty():  # 如果隊列中的數據都處理完了，則強制停止read方法
            pr.terminate()
            break
    print('END')

• 信號量：Semaphore

from multiprocessing import Process, Semaphore
from time import sleep

def write(f):
    f.acquire()
    sleep(5)
    f.release()
    
    
if __name__ == '__main__':
    pp = []
    f = Semaphore(1)
    for i in range(5):
        p = Process(target=write, args=(f,))
        p.start()
        pp.append(p)
    for p in pp:
        p.join()