Is there a way to be notified when a clojure future finishes?

Question

Is there a way to set a watch on a future so that it triggers a callback when it is done?

something like this?

> (def a (future (Thread/sleep 1000) \"         


        

Answer 1

You can start another task that watches the future and then runs the function. In this case I'll just use another future. Which wraps up nicely into a when-done function:

user=> (defn when-done [future-to-watch function-to-call] 
          (future (function-to-call @future-to-watch)))
user=> (def meaning-of-the-universe 
         (let [f (future (Thread/sleep 10000) 42)] 
            (when-done f #(println "future available and the answer is:" %)) 
            f))
#'user/meaning-of-the-universe

... waiting ...

user=> future available and the answer is: 42
user=> @meaning-of-the-universe
42