Suppose I was giving this list of urls:

website.com/thispage
website.com/thatpage
website.com/thispageagain
website.com/thatpageagain
website.com/morepages

... could possibly be over say 1k urls.
What is the best/easiest way to kinda loop through this list and check whether or not the page is up?
Open a pool of threads, open a Url for each, wait for a 200 or a 404. Rinse and repeat.
Given a big list of urls, what is a way to check which are active/inactive?