python 进程池pool使用详解

multiprocessing.Pool( processes )

from multiprocessing import Pool
import os
import time
import random

def worker(msg):
  t_start = time.time()
  print("%s开始执行,进程号为%d" % (msg, os.getpid()))
  # random.random()随机生成0~1之间的浮点数
  time.sleep(random.random()*2)
  t_stop = time.time()
  print(msg, "执行完毕，耗时%0.2f" % (t_stop-t_start))

if __name__ == "__main__":
  po = Pool(3) # 定义一个进程池，最大进程数3
  for i in range(0, 8):
    # Pool().apply_async(要调用的目标,(传递给目标的参数元祖,))
    # 每次循环将会用空闲出来的子进程去调用目标
    po.apply_async(worker, (i,))

  print("----start----")
  # 关闭进程池，关闭后po不再接收新的请求
  po.close()
  # 等待po中所有子进程执行完成，必须放在close语句之后
  po.join()
  print("-----end-----")

RuntimeError: Queue objects should only be shared between processes through inheritance.

from multiprocessing import Manager, Pool
import os
import time
import random

def writer(q):
  print("writer启动(%s),父进程为(%s)" % (os.getpid(), os.getppid()))
  for i in "xiaoming":
    q.put(i)

def reader(q):
  print("reader启动(%s),父进程为(%s)" % (os.getpid(), os.getppid()))
  for i in range(q.qsize()):
    print("reader从Queue获取到消息：%s" % q.get(True))

if __name__ == "__main__":
  print("(%s) start" % os.getpid())
  # 使用Manager中的Queue
  q = Manager().Queue()
  po = Pool()
  po.apply_async(writer, (q,))
  # 先让上面的任务向Queue存入数据，然后再让下面的任务开始从中取数据
  time.sleep(1)
  po.apply_async(reader, (q,))
  po.close()
  po.join()
  print("(%s) End" % os.getpid())

(17528) start
writer启动(2216),父进程为(17528)
reader启动(2216),父进程为(17528)
reader从Queue获取到消息：x
reader从Queue获取到消息：i
reader从Queue获取到消息：a
reader从Queue获取到消息：o
reader从Queue获取到消息：m
reader从Queue获取到消息：i
reader从Queue获取到消息：n
reader从Queue获取到消息：g
(17528) End