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simple job scheduling with a threaded lisp

Yesterday I had a need to do some batch processing, making many HTTP calls to crawl a government website to pull down some public data.  I didn’t want to run this during normal hours, because I didn’t want to put a strain on their server.  I had the web crawling sorted out as a function using drakma and cl-ppcre to get the data I wanted.

I wasn’t sure how best to schedule this function to run later that night, and was about to dig into anacron and figure out the right command-line flags to sbcl, when Nathan suggested the obvious:  why not have lisp schedule it?  It was very easy to throw something together using sleep and get-universal-time.  This morning I abstracted that into a helper function using SBCL Threading:

(defun run-later (utime-to-run function)
   #'(lambda ()
       (sleep (- utime-to-run (get-universal-time)))
       (funcall function))))

Very handy, doesn’t lock my repl, scratches my itch, and easy to write.

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