One thread - one user (threading, python, bot)?

Question

Python

Let's say the /start command starts a thread with a loop.
How to make it so that the user cannot create more than one thread?
Then, after an indefinite amount of time, the user can write the /stop command, which will stop the loop, thereby stopping the thread.
How to make it close the stream of the person who wrote the bot, and not all at once?