import threading import time num = 0 lock = threading.Lock() def increment(): global num lock.acquire() # 获取锁 num += 1 lock.release() # 释放锁 threads = [] for i in range(10000): t = threading.Thread(target=increment) threads.append(t) t.start() end = time.time() print(end - start) for t in threads: t.join() 哪里有错

代码中缺少了变量 start 的定义，应该在创建线程之前定义 start 变量并赋值为当前时间，以便计算线程执行时间。修改后的代码如下：

import threading
import time

num = 0
lock = threading.Lock()

def increment():
    global num
    lock.acquire()  # 获取锁
    num += 1
    lock.release()  # 释放锁

threads = []
start = time.time()  # 定义 start 变量并赋值为当前时间
for i in range(10000):
    t = threading.Thread(target=increment)
    threads.append(t)
    t.start()

for t in threads:
    t.join()

end = time.time()
print(end - start)

注意，计算线程执行时间的代码应该在循环结束后执行，因为 join() 方法会阻塞主线程，直到所有子线程都执行完毕。