python ---- expansion process

Acquisition process and the parent process pid

More open process in memory, operating system, how to distinguish these processes? Each process has a unique identifier,
1. In the terminal view the process of pid.
1. In the process of terminal to view the execution of pid
2. View pid through code
```
import os
import time
print(f'子进程:{os.getpid()}')
print(f'父进程:{os.getppid()}')
time.sleep(5000)
```

Data isolation between the validation process

from multiprocessing import Process
import time
x = 1000
def task(name):
     print(name)
     global x
     x = 2
if __name__ == '__main__':
     p1 = Process(target=task,args=('太白',))
     p1.start()
     time.sleep(3)
     print(f'主进程:{x}')

# 上面已经验证了 子进程与父进程之间的空间隔离.,要验证初始变量是否是一个id.
# 数字-5~256 主进程子进程是沿用同一个.
from multiprocessing import Process
import time
x = 1000
#x = 255
def task(name):
     print(f'子进程:{id(x)}')
if __name__ == '__main__':
     print(f'主进程:{id(x)}')
     p1 = Process(target=task,args=('太白',))
     p1.start()
     time.sleep(3)

join method

join 等待,主进程等待子进程结束之后,在执行
 # p1, p2, p3 三个子进程运行的先后顺序不定.
 # start只是通知一下操作系统,三个start几乎同一时刻发给操作系统,
 # 操作系统调用cpu先运行谁,谁先执行.
 join并不是串行.

from multiprocessing import Process
import time
def task(name,sec):
    time.sleep(sec)
    print(f'{name} is running')
if __name__ == '__main__':
    p1 = Process(target=task,args=('李业',3))
    p2 = Process(target=task, args=('怼哥', 2))
    p3 = Process(target=task, args=('ma', 1))
    start_time = time.time()
    p1.start()
    p2.start()
    p3.start()
    p1.join()
    p2.join()
    p3.join()
    print(f'===主进程:{time.time()-start_time}之后,执行')

Other properties of the process objects

from multiprocessing import Process
import time
def task(name):
    print(f'{name} is running')
    time.sleep(3)
    print(f'{name} is done')
if __name__ == '__main__':
     p = Process(target=task,args=('怼哥',) ,name='任务1')  # name给进程对象设置name属性
     p.start()
     print(p.pid)  # 获取进程pid号
     print(p.name)
     time.sleep(1)
     p.terminate() # 终止(结束)子进程
     #terminate 与 start一样的工作原理: 都是通知操作系统终止或者开启一个子进程,内存中终止或者开启(耗费时间)
     time.sleep(1)
     print(p.is_alive())  # 判断子进程是否存活
     # 只是查看内存中p子进程是否运行.
     print('===主进程')

Zombie process and orphaned

# linux(mac)环境下才强调的两个概念,windows下没有.
# 面试官会问到这两个概念.
from multiprocessing import Process
import time
import os
def task(name):
    print(f'{name} is running')
    print(f'子进程开始了:{os.getpid()}')
    time.sleep(50)
if __name__ == '__main__':
    for i in range(100000):
        p = Process(target=task,args=('怼哥',))
        p.start()
    print(f'主进程开始了:{os.getpid()}')
# 主进程是子进程的发起者,按理说,主进程不会管子进程是否结束,对于结束来说,两个进程是没有任何关系的.
# 但是通过代码我们发现: 主进程并没有结束,实际上你的主进程要等到所有的子进程结束之后,主进程在结束.
# 父进程为什么不关闭?
# 此时主进程形成了僵尸进程:
# 内存中只包含: 主进程的pid,以及子进程的开启时间,结束时间. 至于主进程的代码以及文件,数据库数据等等全部消失.
# 因为主进程要进行收尸环节.
# 利用这个waitepid()方法,对所有的结束的子进程进行收尸.
# 孤儿进程: 此时如果主进程由于各种原因,提前消失了,它下面的所有的子进程都成为孤儿进程了.
#谁给孤儿进程收尸?  一段时间之后, init就会对孤儿进程进行回收.
# 孤儿进程无害,如果僵尸进程挂了,init会对孤儿进程进行回收.
# 僵尸进程有害?
# 父进程(僵尸进程)无限的开启子进程,递归的开启,子进程越来越多,僵尸进程还没有结束,
# 导致进程会越来越多,占用内存.

Daemon

# 守护: 我守护者你,你要是死了,我就跟你一起.
# 子进程对父进程可以进行守护.
# 生产者消费者模型会讲到.
from multiprocessing import Process
import time
import os
def task(name):
    print(f'{name} is running')
    print(f'子进程开始了:{os.getpid()}')
    time.sleep(50)
if __name__ == '__main__':
    p = Process(target=task,args=('怼哥',))
    p.daemon = True  # 将p子进程设置成守护进程,守护主进程,只要主进程结束,子进程无论执行与否,都马上结束.
    p.start()
    time.sleep(2)
    print(f'主进程开始了:{os.getpid()}')

python ---- expansion process

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