MAC OS system used in xcode pthread parallel programming, why time is faster than serial? And the serial program execution, I was with the activity monitor view, the program has two threads in the execution, when I use the pthread create four thread parallel program, the activity monitor shows that there are six threads in executing the program?

Is this normal? If so, why is my parallel programs than serial program takes much?

Please refer to the specific code and results
https://blog.csdn.net/weixin_40996518/article/details/105571502