python 之 Multiprocessing 多进程

参考视频：莫烦python https://mofanpy.com/tutorials/python-basic/multiprocessing/why/

1.创建进程

# -*- coding: utf-8 -*-

import multiprocessing as mp
import threading as td


def job(a,b):
    print('hhhh')
 
    
if __name__=="__main__":
    #t1 = td.Thread(target=job,args=(1,2))
    p1 = mp.Process(target=job,args=(1,2))

    p1.start()
    p1.join()
    
    #t1.start()
    #t1.join()
    

2. queue 进程输出

# -*- coding: utf-8 -*-

import multiprocessing as mp
import threading as td


def job(q):
    res = 0
    for i in range(10):
        res += i+i**2+i**3
    q.put(res)#queue
    
 
    
if __name__=="__main__":
    q = mp.Queue()
    p1 = mp.Process(target=job,args=(q,))
    p2 = mp.Process(target=job,args=(q,))

    p1.start()
    p2.start()
    p1.join()
    p2.join()
    
    res1 = q.get()
    res2 = q.get()
    print("res1",res1)
    print("res2",res1)

res1 2355
res2 2355

3. 多线程和多进程效率对比

# -*- coding: utf-8 -*-

import multiprocessing as mp
import threading as td
import time
from queue import Queue

def job(q):
    res = 0
    for i in range(10000000):
        res += i+i**2+i**3
    q.put(res)#queue

def multcore():
    q = mp.Queue()
    p1 = mp.Process(target=job,args=(q,))
    p2 = mp.Process(target=job,args=(q,))

    p1.start()
    p2.start()
    p1.join()
    p2.join()
    
    res1 = q.get()
    res2 = q.get()
    print("multiprocess:",res1+res2) 
    
def multicore():
    q = Queue()
    t1 = td.Thread(target=job,args=(q,))
    t2 = td.Thread(target=job,args=(q,))

    t1.start()
    t2.start()
    t1.join()
    t2.join()
    
    res1 = q.get()
    res2 = q.get()
    print("multithread:",res1+res2)  
 
def normal():
    res = 0
    for _ in range(2):
        for i in range(10000000):
            res += i+i**2+i**3
    print("normal:",res)
 
if __name__=="__main__":
    st = time.time()
    normal()
    st1 = time.time()
    print('normal time:', st1 - st)
    multicore()
    st2 = time.time()
    print('multithread time:', st2 - st1)
    multicore()
    print('multicore time:', time.time() - st2)

normal: 4999999666666716666660000000
normal time: 13.963502645492554
multithread: 4999999666666716666660000000
multithread time: 14.728559017181396
multithread: 4999999666666716666660000000
multicore time: 13.920192003250122

4.进程池 Pool 

# -*- coding: utf-8 -*-

import multiprocessing as mp

def job(x):
    return x*x

def multicore():
    pool = mp.Pool(processes=12) # 用12个核,默认所有核
    res = pool.map(job,range(100000000))
    print(res)

if __name__ == "__main__":
    multicore()

# -*- coding: utf-8 -*-

import multiprocessing as mp

def job(x):
    return x*x

def multicore():
    pool = mp.Pool() 
    
    # 一个进程
    res = pool.apply_async(job,(2,)) #一次只能再一个进程中计算一个结果
    print(res.get())
    
    # 很多进程
    multi_res = [pool.apply_async(job,(i,)) for i in range (10)]
    print([res.get() for res in multi_res])

if __name__ == "__main__":
    multicore()

4
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

4. 共享内存

# -*- coding: utf-8 -*-

import multiprocessing as mp


value = mp.Value('d',1) # i 表示int, d 表示 浮点 ...
array = mp.Array('i',[1,2,3]) #只能是一维的

5. 锁 Lock

如果没有锁，那么多个进程可能会抢占共享内存中的变量

没有加 lock

# -*- coding: utf-8 -*-

import multiprocessing as mp
import time

def job(v,num):
    for _ in range(10):
        time.sleep(0.1)
        v.value += num
        print(v.value)


def multicore():
    v = mp.Value('i',0)
    p1 = mp.Process(target=job,args=(v,1))
    p2 = mp.Process(target=job,args=(v,3))
    p1.start()
    p2.start()
    p1.join()
    p2.join()
    
if __name__ == "__main__":
    multicore()

    

加了 lock

# -*- coding: utf-8 -*-

import multiprocessing as mp
import time

def job(v,num,l):
    l.acquire()
    for _ in range(10):
        time.sleep(0.1)
        v.value += num
        print(v.value)
    l.release()

def multicore():
    l = mp.Lock()
    v = mp.Value('i',0)
    p1 = mp.Process(target=job,args=(v,1,l))
    p2 = mp.Process(target=job,args=(v,3,l))
    p1.start()
    p2.start()
    p1.join()
    p2.join()
    
if __name__ == "__main__":
    multicore()

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