进程池

import multiprocessing as mp
from time import sleep 
import os 

def worker(msg):
    sleep(2)
    print(msg)
    return "worker return" + msg

#创建进程池对象 ,进程池中包含4个进程
pool = mp.Pool(processes = 4)

result = []
for i in range(10):
    msg = "hello %d"%i 
    #向进程池加入要执行的事件
    r = pool.apply_async(worker,(msg,))
    # pool.apply(worker,(msg,))
    result.append(r)

#获取每个事件函数的返回值
for res in result:
    print(res.get())

#关闭进程池事件加入通道
#即不能再向进程池中加入事件
pool.close()
#阻塞等待进程池处理事件结束后回收进程池
pool.join()

#进程池只有4个进程，所以每次执行结果只有四个结果