开启子进程的两种方式,以及join方法

方式一

在windows系统上,开启子进程的操作必须放到:

if name == 'main':的子代码中

from multiprocessing import Process
import time


def task(name):
    print('%s is running...' % name)
    time.sleep(3)
    print('%s is done' % name)


if __name__ == '__main__':
    p = Process(target=task, args=('子进程...',))
    p.start()
    print('主进程...')

方式二

from multiprocessing import Process
import time


class MyProcess(Process):
    def __init__(self, name):
        super().__init__()
        self.name = name

    def run(self):
        print('%s is running...' % self.name)
        time.sleep(3)
        print('%s is done' % self.name)


if __name__ == '__main__':
    p = MyProcess('子进程...')
    p.start()
    print('主进程...')

join方法

join:让主进程在原地等待,等待子进程运行完毕,不会影响子进程的执行

from multiprocessing import Process
import time

def task(name,n):
    print('%s is running' %name)
    time.sleep(n)
    print('%s is done' %name)

if __name__ == '__main__':
    """
    p1=Process(target=task,args=('子1',1))
    p2=Process(target=task,args=('子2',2))
    p3=Process(target=task,args=('子3',3))

    start=time.time()
    p1.start()
    p2.start()
    p3.start()

    p3.join()
    p1.join()
    p2.join()
    print('主',(time.time()-start))
    """
    start=time.time()
    p_l=[]
    for i in range(1,4):
        p = Process(target=task, args=('子%s' %i, i))
        p_l.append(p)
        p.start()

    for p in p_l:
        p.join()
    print('主', (time.time() - start))

验证:进程之间内存空间相互隔离

from multiprocessing import Process

n=100
def task():
    global n
    n=0

if __name__ == '__main__':
    p=Process(target=task)
    p.start()
    p.join()
    print(n)

打印 n 发现 n 的值还是为100 ,说明子进程内的更改并不会影响到主进程的内存空间,也就是说明了进程之间的内存空间相互隔离

进程对象其他相关的属性或方法

1. 进程pid:每一个进程在操作系统内都有一个唯一的id号,称之为pid

from multiprocessing import Process,current_process
import time

def task():
    print('%s is running' %current_process().pid)
    time.sleep(30)
    print('%s is done' %current_process().pid)

if __name__ == '__main__':
    p=Process(target=task)
    p.start()
    print('主',current_process().pid)

上下两种不同的写法

from multiprocessing import Process,current_process
import time,os

def task():
    print('%s is running 爹是:%s' %(os.getpid(),os.getppid()))
    time.sleep(30)
    print('%s is done 爹是:%s' %(os.getpid(),os.getppid()))


if __name__ == '__main__':
    p=Process(target=task)
    p.start()
    print('主:%s 主他爹:%s' %(os.getpid(),os.getppid()))

2. 进程对象其他相关的属性或方法

from multiprocessing import Process,current_process
import time,os

def task():
    print('%s is running 爹是:%s' %(os.getpid(),os.getppid()))
    time.sleep(30)
    print('%s is done 爹是:%s' %(os.getpid(),os.getppid()))


if __name__ == '__main__':
    p=Process(target=task,name='子进程1')
    p.start()
    # print(p.name)
    p.terminate()
    # time.sleep(0.1)
    print(p.is_alive())
    print('主:%s 主他爹:%s' %(os.getpid(),os.getppid()))