多线程对全局变量修改和单线程对全局变量修改

标签：__ multi 多线程 start sum 修改 time 全局变量 dan

线程过多了，不会比单线程快多少。因为程序可能花时间在线程的转换上了。

import threading import time ind=4 dan_sum=0 multi_sum=0 def single():     for j in range(ind):         for i in range(5000):             print(i*2)             global dan_sum             dan_sum=dan_sum+i*2 def s():     for i in range(5000):         print(i*2)         global multi_sum         multi_sum=multi_sum+i*2 def multi():     threa=[]     for j in range(ind):         threa.append(threading.Thread(target=s))     for t in threa:         t.start()     for t in threa:         t.join() if __name__ == '__main__':     start=time.time()     single()     end=time.time()     sum=0     sum1=0     sum=end-start     start=time.time()     multi()     end=time.time()     sum1=end-start     print('single',sum,'multi',sum1,dan_sum,multi_sum)

标签：__,multi,多线程,start,sum,修改,time,全局变量,dan
From： https://www.cnblogs.com/hahaah/p/17368714.html