线程竞争

code

from threading import Thread
import os,time
 
n=100
 
def work():
    global n
    temp=n
    time.sleep(0.1)
    n=temp-1
 
l=[]
for i in range(100):
    p=Thread(target=work)
    l.append(p)
    p.start()
 
for p in l:
    p.join()
 
 
print(n)    #结果可能为99

outputs

macname@MacdeMacBook-Pro py % python3 cccccc.py
99
macname@MacdeMacBook-Pro py % 

 

由于所有线程初始值都是100，所以最后结果为99

加入线程锁后

 

from threading import Thread, Lock
import os, time
 
 
n = 100
def work():
    global n
    lock.acquire()
    temp = n
    time.sleep(0.1)
    n = temp - 1
    lock.release()
 
 
 
 
if __name__ == '__main__':
    lock = Lock()
    l = []
    for i in range(100):
        p = Thread(target=work)
        l.append(p)
        p.start()
    for p in l:
        p.join()
 
 
    print(n)  #0

outputs

macname@MacdeMacBook-Pro py % python3 cccccc.py
0
macname@MacdeMacBook-Pro py %