进程的进阶

1. 进程的两种方式

   1. 开启进程的第一种方式：

      from multiprocessing import Process
      import time
      
      def task(name):
        print(f'{name} is running')
        time.sleep(1)
        print(f'{name} is gone')
      if __name__ =='__main__':
        p = Process(target = task,args = ('常鑫',))
        p.start()(向操作系统发送一个开启子进程的信号，然后执行下一行)
        操作系统接收到信号，会在内存中开辟一个子进程的空间，copy主进程中的所有资源加载到子进程空间中，然后调用CPU去执行
        开辟子进程开销很大
        print('===主')
        所以永远会先执行主进程的代码

   2. 开辟进程的第二种方式

      from multiprocessing import Process
      import time
      class MyProcess(Process):
        def __init__(self,name):
            super().__init()
            self.name = name
      
        def run(self):
            print(f'{self.name} is running')
            time.sleep(1)
            print(f'{self.name} is gone')
      
      if __name__ =='__main__':
        p = MyProcess('zhangsan')
        p.start()
        print('===主')

   3. 简单应用

2. 获取进程pid

   1. os.getpid() 获取子进程的进程id（PID）
   2. os.getppid()获取主进程的进程id（PID）

   from multiprocessing import Process
   import time
   import os
   def task(name):
    print(f'{os.getpid()}')
    time.sleep(2)
    print(f'{os.getppid()}')
   
   if __name__ =="__main__":
    p = Process(target=task,args = ('长兴',))
    p.start()
    print(f'===主{os.getpid()}')
   子进程中的主进程id是py文件的子进程id

3. 验证进程之间的空间隔离

   1. 不可变得数据类型/可变的数据类型(都是空间隔离)

   from multiprocessing import Process
   import time
   name = '太白'#li = ['丽丽']
   def task():
    global name 
    name = '杆子'
    #li.append('刚子')
    print(f'子进程：{name/li}')
   
   if __name__ == "__main__":
    p = Process(target = task)
    p.start()
    time.sleep(2)
    print(name/li)

4. join（***）让主进程等待子进程结束之后再执行主进程

   1. 单个join（子进程结束之后执行主进程）

   from multiprocessing import Process
   import time
   def task(name):
    print(f'{name} is running')
    time.sleep(2)
    print(f'{name} is gone')
   if __name__ == '__main__':
    p = Process(target = task,args = ('长兴',))
    p.start()
    p.join()
    print('==主开始')

   1. 多个子进程使用join

   from multiprocessing import Process
   import time
   def task(name,sec):
    print(f'{name} is running')
    time.sleep(sec)
    print(f'{name} is gone')
   
   if __name__ == '__main__':
    p1 = Process(target = task,args = ('长兴',1))
    p2 = Process(target = task,args = ('立业',2))
    p3 = Process(target = task,args = ('海狗',3))
    p1.start()
    p2.satrt()
    p3.start()
    #join 只针对主进程，如果join下面多次join，他是不阻塞的
    p1.join()
    p2.join()
    p3.join()
    print(f'==主{time.time() - start_time}')
   
   from multiprocessing import Process
   import time
   def task(name,sec):
    print(f'{name} is running')
    time.sleep(sec)
    print(f'{name} is gone')
   
   if __name__ == '__main__':
    p1 = Process(target = task,args = ('长兴',1))
    p2 = Process(target = task,args = ('立业',2))
    p3 = Process(target = task,args = ('海狗',3))
    p1.start()
    p2.satrt()
    p3.start()
    #join 只针对主进程，如果join下面多次join，他是不阻塞的
    p1.join()
    print(f'==主1：{time.time()-start_time()}')
    p2.join()
    print(f'==主2：{time.time()-start_time()}')
    p3.join()
    print(f'==主3:{time.time() - start_time}')

   1. 优化上面的代码

   from multiprocessing import Process
   import time
   def task(sec):
    print(f'is running')
    time.sleep(sec)
    print(f'is gone')
   
   if __name__ =='__main__':
    p1 = Process(target = task,args = ('长兴',1))
    p2 = Process(target = task,args = ('立业',2))
    p3 = Process(target = task,args = ('海狗',3))
    p1.start()
    p2.satrt()
    p3.start()
    #join 只针对主进程，如果join下面多次join，他是不阻塞的
    p1.join()
    p2.join()
    p3.join()
   
    li =[]
    for i in range(1,4):
        p = Process(target = task,args = (i,))
        li.append(p)
        p.start()
    for i in li:
        i.join()
    print(f'==主：{time.time()-start_time}')
    join就是阻塞，主进程有join,主进程下面的代码一律不执行，直到进程执行完毕之后，再执行  

5. 进程的其他参数

   terminate（）杀死子进程
   is_alive()判断子进程是否存活

   from multiprocessing import Process
   import time
   def task(name):
       print(f'{name} is running')
       time.sleep(2)
       print(f'{name} is gone')
   
   if __name__ == '__main__':
       # p = Process(target=task,args=('长兴',))
       p = Process(target=task,args=('长兴',),name = 'alex')
       p.start()
       time.sleep(1)
       p.terminate()#杀死子进程
       p.join()
       time.sleep(0.5)
       print(p.is_alive())
       print(p.name)
       p.name = 'sb'
       print(p.name)
       print('==主开始')

6. 守护进程：子进程守护着主进程，只要主进程结束，子进程跟着就结束

   from multiprocessing import Process
   import time
   def task(name):
       print(f'{name} is running')
       time.sleep(2)
       print(f'{name} is gone')
   if __name__ == '__main__':
       p = Process(target=task,args = ('常鑫',))
       p.daemon = True#讲子进程设置为守护进程，只要主进程结束，守护进程马上就会结束
       一定要在子进程开始之前设置
       p.start()
       time.sleep(1)
       print('===主')

进程的进阶

原文：https://www.cnblogs.com/-777/p/11385867.html