day29-1 守护进程

守护进程

守护进程会在主进程代码执行结束后和主进程一起终止

# 守护进程
import time
from multiprocessing import Process


def task1():
    print('son1 process run:', time.ctime())
    time.sleep(3)
    print('son1 process stop:', time.ctime())


def task2():
    print('son2 process run:', time.ctime())
    time.sleep(5)
    print('son2 process stop:', time.ctime())


if __name__ == '__main__':
    p1 = Process(target=task1)
    p2 = Process(target=task2)

    p1.daemon = True  # 将p1子进程设为主进程的守护进程，必须要写在开启该子进程的前面
    p1.start()  # 开启进程p1
    p2.start()  # 开启进程p2

    time.sleep(1)
    print('parent process stop:', time.ctime())
-----------------------------------------------------------------
son2 process run: Wed Jul  3 15:34:43 2019  
son1 process run: Wed Jul  3 15:34:43 2019
parent process stop: Wed Jul  3 15:34:44 2019  # 在子进程结束时，p1子进程跟着结束，所以son1 process stop不打印
son2 process stop: Wed Jul  3 15:34:48 2019

守护进程内无法再开启子进程，否则抛出异常：AssertionError: daemonic processes are not allowed to have children

# 在守护进程内开启子进程，抛出异常：AssertionError: daemonic processes are not allowed to have children
import time
from multiprocessing import Process


def task11():
    print('son son process:', time.ctime())

 
def task1():
    p11 = Process(target=task11)
    p11.start()


if __name__ == '__main__':
    p1 = Process(target=task1)

    p1.daemon = True
    p1.start()

    time.sleep(1)
    print('parent process stop:', time.ctime())
-----------------------------------------------------------------------------
Process Process-1:
Traceback (most recent call last):
  File "C:\Python3\lib\multiprocessing\process.py", line 258, in _bootstrap
    self.run()
  File "C:\Python3\lib\multiprocessing\process.py", line 93, in run
    self._target(*self._args, **self._kwargs)
  File "E:\python9\day32\test.py", line 16, in task1
    p11.start()
  File "C:\Python3\lib\multiprocessing\process.py", line 103, in start
    'daemonic processes are not allowed to have children'
AssertionError: daemonic processes are not allowed to have children
parent process stop: Wed Jul  3 15:42:33 2019

# 不设守护进程，在子进程内开启子进程.类似于一种嵌套
import time
from multiprocessing import Process


def task11():
    print('son1 son process:', time.ctime())


def task1():
    p11 = Process(target=task11)
    p11.start()
    time.sleep(1)
    print('son process:',time.ctime())


if __name__ == '__main__':
    p1 = Process(target=task1)
    p1.start()
    time.sleep(1)
    print('parent process stop:', time.ctime())
-----------------------------------------------------------------------------
son1 son process: Wed Jul  3 15:48:34 2019
parent process stop: Wed Jul  3 15:48:34 2019
son process: Wed Jul  3 15:48:35 2019