(并发编程)进程 (multiprocessing--Process实现进程并发）

['创建进程2方式种'，

'进程对象属性：join方法，守护进程obj.daemon=True,obj.pid, obj.name, obj.terminate(),obj.is_alive()等 '

'os.getpid,os.getppid',

'互斥锁(Lock())',

'僵尸进程与孤儿进程',

'内存空间物理上隔离']
并发的本质：切换+保持状态
一、同一个程序执行多次是多个进程
每一个进程有一个PID
import os
os.getppid()   #父的pid (pycharm.exe)#cmd 中 pyhon 路径 父的pid(cmd.exe)
os.getpid()    #自己的pid (python.exe)

二、开启子进程的两种方式
windows (createprocess) 创建子进程时子辈除了拷贝父辈的信息还创建了些自己的东西
unix (fork) 创建子进程时拷贝父辈的信息，子进程的初始状态和父辈一致

第一种（比较常用）                                                                                                                                                                                                           
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__':                                                                                                                                                                                          
    # 在windows系统之上，开启子进程的操作一定要放到这下面                                                                                                                                                                                 
    # Process(target=task,kwargs={'name':'egon'})   #两种传参方式皆可                                                                                                                                                        
    p=Process(target=task,args=('egon',))          #两种传参方式皆可                                                                                                                                                        
    p.start() # 向操作系统发送请求，操作系统会申请内存空间，把父进程的数据拷贝给子进程，作为子进程的初始状                                                                                                                          
    print('======主')                                                                                                                                                                                                
                                                                                                                                                                                                                    
第二种                                                                                                                                                                                                                 
from multiprocessing import Process                                                                                                                                                                                 
import time                                                                                                                                                                                                         
                                                                                                                                                                                                                    
class MyProcess(Process):                                                                                                                                                                                           
    def __init__(self,name):                                                                                                                                                                                        
        super(MyProcess,self).__init__()     #Process在init里面有相应设置，要遗传下来，否则报错                                                                                                                                        
        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('egon')                                                                                                                                                                                             
    p.start()   #p.start()调用了类中的run（）方法（规定）                                                                                                                                                                         
print('主')

三、进程的内存空间相互隔离
from multiprocessing import Process                    
import time                                            
                                                       
x=1000                                                                                                       
def task():                                            
    time.sleep(3)                                      
    global x                                           
    x=0                                                
    print('儿子死啦',x)                                    

#在之前最好只有函数或变量的定义，没有具体的执行（print等）                                                       
if __name__ == '__main__':                                                                      
    p=Process(target=task)                             
    p.start()                                          
    time.sleep(5)                                      
print(x)    
#在子进程中对变量x的修改不影响父进程中x的值

四、父进程等待子进程结束 p1.join()

#（等待p1 卡住）等儿子死了，wait回收儿子的pid等遗留下的东西
#了解 连续start再连续join 和 连续start，join。。。。
from multiprocessing import Process                                    
import time                                                            
                                                                       
x=1000                                                                                        
def task(n):                                                           
    print('%s is runing' %n)                                           
    time.sleep(n)                                                      
                                                                       
if __name__ == '__main__':                                             
    start_time=time.time()                                             
                                                                       
    p1=Process(target=task,args=(1,))                                  
    p2=Process(target=task,args=(2,))                                  
    p3=Process(target=task,args=(3,))                                  
    p1.start()                                                         
    p2.start()                                                         
    p3.start()                                                         
                                                                       
    p3.join() #3s                                                      
    p1.join()                                                          
    p2.join()                                                      
                                                                       
print('主',(time.time() - start_time))        #3.01637601852417     

#用循环
from multiprocessing import Process                                  
import time                                                          
                                                                     
x=1000                                                               
                                                                     
def task(n):                                                         
    print('%s is runing' %n)                                         
    time.sleep(n)                                                    
                                                                     
if __name__ == '__main__':                                           
    start_time=time.time()                                           
    p_l=[]                                                           
    for i in range(1,4):                                             
        p=Process(target=task,args=(i,))                             
        p_l.append(p)                                                
        p.start()                                                    
                                                                     
    for p in p_l:                                                    
        p.join()                                                     
                                                                     
print('主',(time.time() - start_time))       #3.0141923427581787

五、进程对象的其他属性
from multiprocessing import Process                                     
import time                                                             
                                                                        
def task(n):                                                            
    print('%s is runing' %n)                                            
    time.sleep(n)                                                       
                                                                        
if __name__ == '__main__':   # 在windows系统之上，开启子进程的操作一定要放到这下面                                            
    start_time=time.time()                                              
    p1=Process(target=task,args=(1,),name='任务1') 
    p1daemon=True    #再obj发出创建前，将obj变成守护进程，主进程执行完毕后子进程跟着结束
    p1.start()         #向操作系统发创建子进程请求，父进程无需等待                                                    
    print(p1.pid)                                                       
    print(p1.name)     #如前面不定义name，默认process-1 etc                      
    p1.terminate()     #向操作系统发请求，父进程无需等待                            
    p1.join()          #等待该子进程结束（卡住吧），父进程需要等待一点时间                                                
    print(p1.is_alive())                                                
    print('主')       #这里的效果是主进程等儿子死了，再结束

from multiprocessing import Process                         
import time,os                                              
                                                            
def task():                                                 
    print('self:%s parent:%s' %(os.getpid(),os.getppid()))  
    time.sleep(3)                                           
                                                            
if __name__ == '__main__':                                  
    p1=Process(target=task,)                                
    p1.start()                                              
    print(p1.pid)                                           
print('主',os.getpid())  

六、僵尸进程与孤儿进程
在unix系统中init是所有进程的爹；创建进程用fork，回收进程（结束进程的残留信息？）用waitpid
僵尸进程（有害：占用pid）：子代先于父代终结，其部分信息（pid等）没有从系统中删除，需要父代回收。join中含有回收子代信息的功能。
孤儿进程（无害）：父代先于子代终结，子代终结后的部分信息由init代收。

from multiprocessing import Process                     
import time,os                                          
                                                        
def task(n):                                            
    print('%s is running' %n)                           
    time.sleep(n)                                       
                                                        
if __name__ == '__main__':       
 1=Process(target=task,args=(1,))                   
    p1.start()                                          
    p1.join()     # join中含有回收子代信息的功能（wait）                                      
    print('======主',os.getpid()) 
 

 
七、守护进程

父进程  代码运行完(主线程运行代码)，守护进程就结束
from multiprocessing import Process
import time

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

if __name__ == '__main__':
    obj = Process(target=task, args=('egon',))
    obj.daemon=True    #将obj变成守护进程，主进程执行完毕后子进程跟着结束
    obj.start()  # 发送信号给操作系统
　 print('主')

八、互斥锁
强调：必须是lock.acquire()一次，然后 lock.release()释放一次，才能继续lock.acquire()，不能连续的lock.acquire()。否者程序停在原地。
   　　抢同一把锁：生成锁对象 必须放在if __name__=='__main__': 下面
互斥锁vs join：
大前提：二者的原理都是一样，都是将并发变成串行，从而保证有序（在多个程序共享一个资源时，为保证有序不乱，需将并发变成串行）
场景: 修改公共数据，如果并发会发出数据错乱，这时就必须串行执行，就要用到互斥锁
区别一：join是按照人为指定的顺序执行，而互斥锁是所以进程平等地竞争，谁先抢到谁执行
区别二：互斥锁可以让一部分代码串行，而join只能将代码整体串行（详见抢票系统）
  理解：首先join肯定是一个子进程对象，互斥锁可以加在子进程对象代码任意部位（要释放额）
     join人为安排子进程执行顺序，互斥锁是公平竞争。
  
from multiprocessing import Process,Lock
import time,random

mutex=Lock()  #这里每个子进程的都会申请一把锁
print(id(mutex))

def task1(lock):
     lock.acquire()
 #   print('task1:名字是egon')
 #   time.sleep(random.randint(1,3))
 #   print('task1:性别是male')
     time.sleep(random.randint(1,3))      #with mutex: time.sleep(random.randint(1,3))
 #   print('task1:年龄是18')        
     lock.release()

def task2(lock):
    lock.acquire()
    print('task2:名字是alex')
    time.sleep(random.randint(1,3))
    print('task2:性别是male')
    time.sleep(random.randint(1,3))
    print('task2:年龄是78')
    lock.release()

def task3(lock):
    lock.acquire()
    print('task3:名字是lxx')
    time.sleep(random.randint(1,3))
    print('task3:性别是female')
    time.sleep(random.randint(1,3))
    print('task3:年龄是30')
    lock.release()

if __name__ == '__main__':
    p1=Process(target=task1,args=(mutex,))
    p2=Process(target=task2,args=(mutex,))
    p3=Process(target=task3,args=(mutex,))

    p1.start()
    p2.start()
    p3.start()

last、抢票系统
import json
import time
import random
import os
from multiprocessing import Process,Lock

mutex=Lock()  #每个子进程都会生成  一把锁对象，没用到。可以优化放在下面 __name__里面

def search():
    time.sleep(random.randint(1,3))
    with open('db.json','r',encoding='utf-8') as f:
        dic=json.load(f)
        print('%s 剩余票数:%s' %(os.getpid(),dic['count']))

def get():
    with open('db.json','r',encoding='utf-8') as f:
        dic=json.load(f)
    if dic['count'] > 0:
        dic['count']-=1
        time.sleep(random.randint(1,3))
        with open('db.json','w',encoding='utf-8') as f:
            json.dump(dic,f)
        print('%s 购票成功' %os.getpid())

def task(lock):
    search()
    lock.acquire()
    get()
    lock.release()

if __name__ == '__main__':
    for i in range(10):
        p=Process(target=task,args=(mutex,)) #这里子进程用的都是主进程这一把锁 id
        p.start()