多进程(一)

1.进程创建的两种方式

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(2)
    print(f'{name} is done')

if __name__ == '__main__':  
    #windows环境,开启进程必须在__name__ == '__main__'下
    p = Process(target = task,args = ('alex',))
    #创建一个进程对象
    p.start()
    #只是向操作系统发出一个开辟子进程的信号,然后就执行下一行了
    #操作系统收到信号后,会从内存中开辟一个子进程空间,然后再将主进程所有数据copy到子进程,然后再调用cpu去执行(开辟子进程开销很大),所以永远会先执行主进程的代码
    print('主进程运行')
    
#主进程运行
#alex is running
#alex is done
    
开启进程的第二种方式:
    
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(2)
        print(f'{self.name} is done')
        
if __name__ == '__main__':
    p = MyProcess('alex')
    p.start()
    print('主进程运行')
    
#主进程运行
#alex is running
#alex is done

简单应用:
    
from multiprocessing import Process
import time

def task(name):
    print(f'{name} is running')
    time.sleep(1)
    print(f'{name} is done')
    
def task1(name):
    print(f'{name} is running')
    time.sleep(2)
    print(f'{name} is done')
    
if __name__ == '__main__':
    p1 = Process(target = task,args = ('alex',))
    p2 = Process(target = task,args = ('tony',))
    start_time = time.time()
    p1.start()
    p2.start()
    #两个进程,并发或者并行的执行三个任务
    print(f'结束时间{time.time() - start_time}')
    
#结束时间0.03194904327392578
#alex is running
#tony is running 
#alex is done
#tony is done

2.获取进程pid

区分内存中的进程:
    命令行:获取所有进程的pid(process id): tasklist,
          查找某个进程的pid:  tasklist|findstr 进程名

    代码级别:
            import os
            print(os.getpid())
            
获取父进程(主进程的pid):
    import os
    print(os.getppid())

3.验证进程之间的空间隔离

from multiprocessing import Process
import time

name = 'alex'
def task():
    global name
    name = 'tom'
    print(f'子进程:{name}')

if __name__ == '__main__':
    p = Process(target = task)
    p.start()
    time.sleep(3)
    print(f'主进程:{name}')
    
#子进程:tom
#主进程:alex

lst = [1,2]
def task():
    global lst
    lst.append(3)
    print(f'子进程:{lst}')

if __name__ == '__main__':
    p = Process(target = task)
    p.start()
    time.sleep(3)
    print(f'主进程:{lst}')

#子进程:[1, 2, 3]
#主进程:[1, 2]

4.join方法

join:让主进程等待子进程结束之后,再执行主进程
 
from multiprocessing import Process
import time

def task(name):
    print(f'{name} is running')
    time.sleep(2)
    print(f'{name} is done')
 
if __name__ == '__main__':
    p = Process(target = task,args = ('alex',))
    p.start()
    p.join()
    print('主进程开始')
    
#alex is running
#alex is done
#主进程开始

多个子进程使用join,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,在执行.
验证1:

from multiprocessing import Process
import time

def task(name,sec):
    print(f'{name} is running')
    time.sleep(sec)
    print(f'{name} is done')
    
if __name__ == '__main__':
    start_time = time.time()
    p1 = Process(target = task,args = ('alex',1))
    p2 = Process(target = task,args = ('tom',2))
    p3 = Process(target = task,args = ('tony,3'))
    p1.start()
    p2.start()
    p3.start()
    p1.join() #join只针对主进程,如果join下面多次join,则不阻塞
    p2.join()
    p3.join()
    print(f'主进程:{time.time() - start_time}')
    
#alex is running
#tom is running
#tony is running
#alex is done
#tom is done
#tony is done
#主进程:3.1952016353607178

验证2:
  
from multiprocessing import Process
import time

def task(name,sec):
    print(f'{name} is running')
    time.sleep(sec)
    print(f'{name} is done')
    
if __name__ == '__main__':
    start_time = time.time()
    p1 = Process(target = task,args = ('alex',1))
    p2 = Process(target = task,args = ('tom',2))
    p3 = Process(target = task,args = ('tony,3'))
    p1.start()
    p1.join()
    p2.start()
    p2.join()
    p3.start()
    p3.join()
    print(f'主进程:{time.time() - start_time}')

#alex is running
#alex is done
#tom is running
#tom is done
#tony is running
#tony is done
#主进程:6.42280125617981

优化上面的代码:
 
from multiprocessing import Process
import time

def task(name,sec):
    print(f'{name} is running')
    time.sleep(sec)
    print(f'{name} is done')
    
if __name__ == '__main__':
    start_time = time.time()
    lst = []
    for i in range(1,4):
        p = Process(target = task,args = (i,))
        lst.append(p)
        p.start()     #循环时间很快,基本可以实现同时发出指令
    for i in lst:
        i.join()
    print(f'主进程:{time.time() - start_time}')

5.进程的其他属性

from multiprocessing import Process
import time

def task(name):
    print(f'{name} is running')
    time.sleep(2)
    print(f'{name} is done')
    
if __name__ == '__main__':
    p = Process(target = task,args = ('alex',)name = 'tony')
    p.start()
    p.terminate()  #杀死子进程,没有阻塞则子程序还没运行就被杀死
    print(P.is_alive())   #看子进程是否还活着,输出True/False 
    print(p.name)  #输出之前给p添加的name属性
    print("主进程运行")

6.守护进程

守护进程:
    子进程守护主进程,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 done')
    
if __name__ == '__main__':
    p = Process(target = task,args = ('alex',))
    p.daemon = True #将子进程p设置成守护进程,主进程结束,子进程也结束
    p.start()
    #p.daemon = True #一定要在子进程开启之前设置,否则报错
    time.sleep(1)
    print('主进程运行')
    
#alex is running
#主进程运行

多进程(一)

原文：https://www.cnblogs.com/tutougold/p/11391385.html