041.Python守护进程，锁信号量和事件

一 守护进程

1.1 基本概念

守护进程

• 正常情况下,主进程默认等待子进程调用结束之后结束
• 守护进程在主进程执行代码结束后,自动终止

守护进程语法:

• 进程对象.daemon = True ，设置该进程是守护进程
• 守护进程需要在start()方法之前设置
• 为主进程守护,主进程如果代码执行结束了,该守护进程自动结束.

1.2 基本语法

import os
import time
from multiprocessing import Process
def func():
        print("子进程start")
        print("子进程end")
p = Process(target=func)
p.start()
print ("主进程执行结束")

执行

[ python]# python3 test.py
主进程执行结束
子进程start
子进程end

使用守护进程

import os
import time
from multiprocessing import Process
def func():
        print("子进程start")
        print("子进程end")
p = Process(target=func)
p.daemon = True
p.start()
print ("主进程执行结束")

执行

[ python]# python3 test.py
主进程执行结束

主进程执行完之后，子进程不在执行

1.3 多个子进程情况

import os
import time
from multiprocessing import Process
def func1():
        count = 1
        while True:
                print ("*" * count)
                time.sleep(0.5)
                count += 1
def func2():
        print("func2 start")
        time.sleep(3)
        print("func2 end")
p1 = Process(target=func1)
p1.start()
p2 = Process(target=func2)
p2.start()
print ("主进程执行结束")

执行

[ python]# python3 test.py
主进程执行结束
*
func2 start
**
***
****
*****
******
func2 end
*******
********
*********
**********
***********
************
*************
**************
***************
****************
*****************
******************
*******************
********************
*********************
**********************

第一个进程不能结束，设置一个守护进程

import os
import time
from multiprocessing import Process
def func1():
        count = 1
        while True:
                print ("*" * count)
                time.sleep(0.5)
                count += 1
def func2():
        print("func2 start")
        time.sleep(3)
        print("func2 end")
p1 = Process(target=func1)
p1.daemon = True
p1.start()
p2 = Process(target=func2)
p2.start()
print ("主进程执行结束")

但这种添加还没来得及执行，就被杀掉

执行

[ python]# python3 test.py
主进程执行结束
func2 start
func2 end

当多个子进程并发执行时,默认主进程等待子进程的

如果标记该子进程是守护进程，当主进程执行完所有代码之后,守护进程立刻终止

主进程代码执行到最后一行,就意味着守护进程终止了，其他非守护进程继续执行,主进程仍然会等待他执行结束，最后主进程在真正的释放结束.

1.4 守护进程用途: 报活功能

import os
import time
from multiprocessing import Process
def alive():
        while True:
                print ("I am the first server,I‘m  OK")
                time.sleep(0.5)
def func():
        print("The first server is used to collect logs")
        time.sleep(5)   #相当于这个进程存活5s
p1 = Process(target=alive)
p1.daemon = True
p1.start()
p2 = Process(target=func)
p2.start()
#模拟func程序结束，或者服务器宕机,停止保活,这是执行主进程，执行完，则子进程不在执行，即停止报活
p2.join()
print (".......")

执行

[ python]# python3 test.py
I am the first server,I‘m  OK
The first server is used to collect logs
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
I am the first server,I‘m  OK
.......

二 lock锁

语法:
# 创建一把锁
lock = lock()
# 上锁
lock.acquire()
# 解锁
lock.release()

2.1 基本用法

import os
import time
from multiprocessing import Process,Lock
lock = Lock()
lock.acquire()
lock.release()
print (111)

执行

[ python]# python3 test.py
111

死锁 上锁和解锁之间不匹配,只上锁不解锁就是死锁,会产生阻塞;

import os
import time
from multiprocessing import Process,Lock
lock = Lock()
lock.acquire()
#lock.release()
print (111)

执行就会被阻塞，而且不会打印111，成了一把死锁

2.2 模拟一个抢票机制

假设只有一张票

[ python]# vim ticket

{"count": 1}

抢票方法

import os
import time,json
from multiprocessing import Process,Lock
def wr_info(sign,dic=None):
        if sign == "r":
                with open("ticket",mode="r",encoding="utf-8") as fp:
                        dic = json.load(fp)
                return dic
        elif sign == "w":
                with open("ticket",mode="w",encoding="utf-8") as fp:
                        json.dump(dic,fp)

#抢票方法
def get_ticket(person):
        dic = wr_info("r")
        time.sleep(0.11)
        if dic["count"] > 0:
                print("%s抢到票"%(person))
                dic["count"] -=1
#               更新数据库
                wr_info("w",dic)
        else:
                print ("%s没有买到票"%(person))


#用ticket来仅从统一调用
def ticket(person):
        #查询票数
        dic = wr_info("r")
        print ("%s查询余票：%s"%(person,dic[‘count‘]))
        get_ticket(person)

for i in range(10):
        p = Process(target = ticket,args=( "person%s" %(i), ))
        p.start()

执行

[ python]# python3 test.py
person0查询余票：1
person1查询余票：1
person2查询余票：1
person3查询余票：1
person4查询余票：1
person5查询余票：1
person6查询余票：1
person7查询余票：1
person8查询余票：1
person9查询余票：1
person3抢到票
person0抢到票
person4抢到票
person5抢到票
person1抢到票
person7抢到票
person2抢到票
person6抢到票
person8抢到票
person9抢到票

发现所有人都抢到票了

2.3 使用锁机制

在主进程创建一把锁，在抢票处上锁，然后再抢完解锁，如下操作

import os
import time,json
from multiprocessing import Process,Lock
def wr_info(sign,dic=None):
        if sign == "r":
                with open("ticket",mode="r",encoding="utf-8") as fp:
                        dic = json.load(fp)
                return dic
        elif sign == "w":
                with open("ticket",mode="w",encoding="utf-8") as fp:
                        json.dump(dic,fp)

#抢票方法
def get_ticket(person):
        dic = wr_info("r")
        time.sleep(0.11)
        if dic["count"] > 0:
                print("%s抢到票"%(person))
                dic["count"] -=1
#               更新数据库
                wr_info("w",dic)
        else:
                print ("%s没有买到票"%(person))


#用ticket来仅从统一调用
#这里需要把lock传进来
def ticket(person,lock):
        #查询票数
        dic = wr_info("r")
        print ("%s查询余票：%s"%(person,dic[‘count‘]))
        lock.acquire()
        get_ticket(person)
        lock.release()
lock = Lock()
for i in range(10):
        p = Process(target = ticket,args=( "person%s" %(i), ))
        p.start()

执行

主进程在执行ticket的子进程时，多一个参数

import os
import time,json
from multiprocessing import Process,Lock
def wr_info(sign,dic=None):
        if sign == "r":
                with open("ticket",mode="r",encoding="utf-8") as fp:
                        dic = json.load(fp)
                return dic
        elif sign == "w":
                with open("ticket",mode="w",encoding="utf-8") as fp:
                        json.dump(dic,fp)

#抢票方法
def get_ticket(person):
        dic = wr_info("r")
        time.sleep(0.11)
        if dic["count"] > 0:
                print("%s抢到票"%(person))
                dic["count"] -=1
#               更新数据库
                wr_info("w",dic)
        else:
                print ("%s没有买到票"%(person))


#用ticket来仅从统一调用
#这里需要把lock传进来
def ticket(person,lock):
        #查询票数
        dic = wr_info("r")
        print ("%s查询余票：%s"%(person,dic[‘count‘]))
        lock.acquire()
        get_ticket(person)
        lock.acquire()
lock = Lock()
for i in range(10):
        p = Process(target = ticket,args=( "person%s" %(i), lock))
        p.start()

执行

[ python]# python3 test.py
person0查询余票：1
person1查询余票：1
person2查询余票：1
person3查询余票：1
person4查询余票：1
person5查询余票：1
person6查询余票：1
person7查询余票：1
person8查询余票：1
person9查询余票：1
person0抢到票
person1没有买到票
person2没有买到票
person3没有买到票
person4没有买到票
person5没有买到票
person6没有买到票
person7没有买到票
person8没有买到票
person9没有买到票

或者直接加锁

import os
import time,json
from multiprocessing import Process,Lock
def wr_info(sign,dic=None):
        if sign == "r":
                with open("ticket",mode="r",encoding="utf-8") as fp:
                        dic = json.load(fp)
                return dic
        elif sign == "w":
                with open("ticket",mode="w",encoding="utf-8") as fp:
                        json.dump(dic,fp)

#抢票方法
def get_ticket(person):
        dic = wr_info("r")
        time.sleep(0.11)
        if dic["count"] > 0:
                print("%s抢到票"%(person))
                dic["count"] -=1
                #更新数据库
                wr_info("w",dic)
        else:
                print ("%s没有买到票"%(person))


#用ticket来进行统一调用
#这里需要把lock传进来
def ticket(person):
        #查询票数
        dic = wr_info("r")
        print ("%s查询余票：%s"%(person,dic[‘count‘]))
        lock.acquire()
        #开始抢票
        get_ticket(person)
        lock.release()

lock = Lock()
for i in range(10):
        p = Process(target = ticket,args=( "person%s"%(i),))
        p.start()

区分同步和异步

• 在产生进程对象的时候,进程之间是异步的.上锁之后,进程是同步的
• 必须等上一个进程执行完毕之后,下一个进行才能执行,这个是同步.

三  信号量

Semaphore 本质上就是锁,只不过可以控制锁的数量

模拟取钱，假设10个人排队取钱

import os
import time,json
from multiprocessing import Process,Lock,Semaphore

def bank(person):
        print ("%s进入柜台取钱"%(person))
        print ("%s取完离开"%(person))


for i in range(10):
        p = Process(target = bank,args=("person%s"%(i),))
        p.start()

执行

[ python]# python3 test.py
person0进入柜台取钱
person0取完离开
person1进入柜台取钱
person1取完离开
person2进入柜台取钱
person2取完离开
person3进入柜台取钱
person3取完离开
person4进入柜台取钱
person4取完离开
person5进入柜台取钱
person5取完离开
person6进入柜台取钱
person6取完离开
person7进入柜台取钱
person7取完离开
person8进入柜台取钱
person8取完离开
person9进入柜台取钱
person9取完离开

假设4个柜台使用semaphore上四把锁

import os
import time,json
from multiprocessing import Process,Lock,Semaphore

def bank(person):
        sem.acquire()
        time.sleep(5)
        print ("%s进入柜台取钱"%(person))
        print (os.getpid())
        res = os.popen("date").read()
        print(res)
        sem.release()
        print ("%s取完离开"%(person))

sem = Semaphore(4)
for i in range(10):
        p = Process(target = bank,args=("person%s"%(i),))
        p.start()

执行

person0进入柜台取钱
person3进入柜台取钱
4502
4505
Sat Feb 22 21:58:07 EST 2020
Sat Feb 22 21:58:07 EST 2020


person0取完离开
person3取完离开
person1进入柜台取钱
4503
Sat Feb 22 21:58:07 EST 2020

person1取完离开
person2进入柜台取钱
4504
Sat Feb 22 21:58:07 EST 2020

person2取完离开
person5进入柜台取钱
4507
Sat Feb 22 21:58:12 EST 2020

person5取完离开
person6进入柜台取钱
4508
Sat Feb 22 21:58:12 EST 2020

person6取完离开
person7进入柜台取钱
person4进入柜台取钱
4506
4509
Sat Feb 22 21:58:12 EST 2020

person4取完离开
Sat Feb 22 21:58:12 EST 2020

person7取完离开
person8进入柜台取钱
4510
Sat Feb 22 21:58:17 EST 2020

person8取完离开
person9进入柜台取钱
4511
Sat Feb 22 21:58:17 EST 2020

person9取完离开

根据时间，每次四个一次

四 事件

4.1 基本概念

阻塞事件 ：

1. e = Event()生成事件对象e
2. e.wait()动态给程序加阻塞 , 程序当中是否加阻塞完全取决于该对象中的is_set()

[默认返回值是False]

• 如果是True 不加阻塞
• 如果是False 加阻塞

控制这个属性的值

•  set()方法 将这个属性的值改成True
•  clear()方法 将这个属性的值改成False
•  is_set()方法 判断当前的属性是否为True (默认上来是False)

4.2 基本语法

默认时False

from multiprocessing import Process,Event
e = Event()
print (e.is_set())

执行

[ python]# python3 test.py
False

使用阻塞

from multiprocessing import Process,Event
e = Event()
print (e.is_set())
e.wait(5)   #相当于sleep
print ("事件")

执行

[ python]# python3 test.py
False
事件

set

from multiprocessing import Process,Event
e = Event()
e.set()
print (e.is_set())
e.wait()
print ("事件")

执行，直接打印

[ python]# python3 test.py
True    #不加阻塞
事件

Claen

e = Event() # True
e.set()
e.wait()
print(123)
e.clear() # False
e.wait()
print(456)

执行，456不会打印，因为clean后时False

[ python]# python3 test.py
123

4.3 模拟红绿灯效果

from multiprocessing import Process,Event
import time
def traffic_light(e):
        #默认红灯先亮
        print ("red")
        while True:
                if e.is_set():
                        #当前时绿灯
                        time.sleep(2)
                        #等完2秒，变红灯
                        print("red")
                        e.clear()
                else:
                        #当前时红灯
                        time.sleep(2)
                        #等完2秒，变绿灯
                        print ("blue")
                        e.set()
e = Event()
traffic_light(e)

执行

[ python]# python3 test.py
red
blue
red
blue
red

模拟车辆遇到红灯停，绿灯行

from multiprocessing import Process,Event
import time,random
def traffic_light(e):
        #默认红灯先亮
        print ("red")
        while True:
                if e.is_set():
                        #当前时绿灯
                        time.sleep(2)
                        #等完2秒，变红灯
                        print("red")
                        e.clear()
                else:
                        #当前时红灯
                        time.sleep(2)
                        #等完2秒，变绿灯
                        print ("blue")
                        e.set()

def car(e,i):
        if not e.is_set():
                print ("The car%s is wait"%(i))
                e.wait()
        print("car%s is running"%(i))


e = Event()
p1 = Process(target=traffic_light,args=(e,))
p1.start()

for i in range(20):
        time.sleep(random.uniform(0,2))
        p2 = Process(target=car,args = (e,i))
        p2.start()

执行

[ python]# python3 test.py
red
The car0 is wait
blue
car0 is running
car1 is running
red
The car2 is wait
blue
car2 is running
car3 is running
car4 is running
red
The car5 is wait
blue
car5 is running
car6 is running
red
The car7 is wait
The car8 is wait
The car9 is wait
The car10 is wait
blue
car10 is running
car8 is running
car9 is running
car7 is running
car11 is running
red
The car12 is wait
blue
car12 is running
car13 is running
car14 is running
red
The car15 is wait
The car16 is wait
blue
car15 is running
car16 is running
car17 is running
car18 is running
red
The car19 is wait
blue
car19 is running
red

4.4 使用守护进程

from multiprocessing import Process,Event
import time,random
def traffic_light(e):
        #默认红灯先亮
        print ("red")
        while True:
                if e.is_set():
                        #当前时绿灯
                        time.sleep(2)
                        #等完2秒，变红灯
                        print("red")
                        e.clear()
                else:
                        #当前时红灯
                        time.sleep(2)
                        #等完2秒，变绿灯
                        print ("blue")
                        e.set()

def car(e,i):
        if not e.is_set():
                print ("The car%s is wait"%(i))
                e.wait()
        print("car%s is running"%(i))


e = Event()
p1 = Process(target=traffic_light,args=(e,))
p1.daemon = True
p1.start()

for i in range(20):
        time.sleep(random.uniform(0,2))
        p2 = Process(target=car,args = (e,i))
        p2.start()

执行

red
The car0 is wait
The car1 is wait
The car2 is wait
blue
car0 is running
car1 is running
car2 is running
car3 is running
car4 is running
car5 is running
car6 is running
red
The car7 is wait
The car8 is wait
The car9 is wait
The car10 is wait
blue
car8 is running
car7 is running
car9 is running
car10 is running
car11 is running
red
The car12 is wait
blue
car12 is running
car13 is running
car14 is running
red
The car15 is wait
blue
car15 is running
car16 is running
car17 is running
red
The car18 is wait
The car19 is wait

卡在这里不执行，是因为car已经跑完，进程不再执行，卡在e.wait这里

使用join

from multiprocessing import Process,Event
import time,random
def traffic_light(e):
        #默认红灯先亮
        print ("red")
        while True:
                if e.is_set():
                        #当前时绿灯
                        time.sleep(2)
                        #等完2秒，变红灯
                        print("red")
                        e.clear()
                else:
                        #当前时红灯
                        time.sleep(2)
                        #等完2秒，变绿灯
                        print ("blue")
                        e.set()

def car(e,i):
        if not e.is_set():
                print ("The car%s is wait"%(i))
                e.wait()
        print("car%s is running"%(i))


e = Event()
lst = []
p1 = Process(target=traffic_light,args=(e,))
p1.daemon = True
p1.start()

for i in range(20):
        time.sleep(random.uniform(0,2))
        p2 = Process(target=car,args = (e,i))
        p2.start()
        lst.append(p2)
for i in lst:
        i.join()
print("程序彻底结束;")

执行

red
The car0 is wait
The car1 is wait
blue
car1 is running
car0 is running
car2 is running
car3 is running
red
The car4 is wait
blue
car4 is running
car5 is running
car6 is running
car7 is running
red
The car8 is wait
The car9 is wait
blue
car9 is running
car8 is running
car10 is running
red
The car11 is wait
blue
car11 is running
car12 is running
car13 is running
car14 is running
red
The car15 is wait
blue
car15 is running
car16 is running
car17 is running
red
The car18 is wait
The car19 is wait
blue
car19 is running
car18 is running
程序彻底结束;