UDF framework doesn't clean up the resources used by the user

[avinash0161]

If the user creates threads in his UDF code, but forgets to destroy them, our UDF framework should destroy those threads. This issue was seen in the issue here #1141 . As a temporary fix, we can tell users to make sure they are destroying all threads, but it can be difficult if user himself is using a third party library.

So, we should try to incorporate logic in the UDF framework, to destroy the resources user has created.

[zuozhiw]

Discussion 1/13: we need further deeper investigation

[Xiao-zhen-Liu]

Discussion 2022.05.12: Related to this issue. We leave it open.

[Xiao-zhen-Liu]

Discussion 2022.12.07: Won't be fixed in the near future.