import threading
import time


def count(n):
    start_time_inner = time.time()
    for i in range(n):
        sum(range(1000000000))
    end_time_inner = time.time()
    print("Function time taken: {:.2f} seconds".format(end_time_inner -
                                                       start_time_inner))
  

# 多线程运行时间
start_time = time.time()
t1 = threading.Thread(target=count, args=(2, ))
t2 = threading.Thread(target=count, args=(2, ))
# t1.daemon = False
t1.start()
t2.start()
t1.join()
t2.join()
end_time = time.time()
print("Multi-thread total time taken: {:.2f} seconds".format(end_time -
                                                             start_time))

上面的代码执行结果：

Function time taken: 58.98 seconds
Function time taken: 39.23 seconds
Multi-thread total time taken: 78.57 seconds

为什么在子线程都t1.join() t2.join()，主线程应该在等待两个子线程运行结束后，才执行join()方法后面的代码，也就是end_time的时间获取。

那么为什么实际结果，主线程所用的时间78.57s，并不是两个线程运行时间之和