C #: Why does a process exist in the background when the program is closed?

I also saw a friend who had this problem and didn't care about it at the time. I have encountered this problem in my project. I will make some research and share it with you.

The reason for this problem in my project is the creation and termination of the thread.

There are two solutions:

A: When a thread is created, specify that the thread is a background thread (. The isbackground attribute is true). When the main thread is closed, it will also be closed.

B: If the thread is not set to a background thread, it must be manually closed, but it may be that the abort is not clean or the thread will not be closed when it is waiting.