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多线程-共享全局变量问题

多线程可能遇到的问题

假设有两个线程t1和t2，都要对一个变量g_num进行运算(+1)，两个线程t1和t2分别对g_num各加10次，g_num的最终结果。

import threading
import time

g_num = 0
def work1(num):
    global g_num
    for i in range(num):
        g_num += 1
    print('in work1:',g_num)


def work2(num):
    global g_num
    for i in range(num):
        g_num += 1
    print('in work2:', g_num)

print('---线程创建之前：%d' % g_num)

t1 = threading.Thread(target=work1,args=(10,))
t2 = threading.Thread(target=work2,args= (10,))
t1.start()
t2.start()

while len(threading.enumerate())!=1:
    time.sleep(