clojure - 有没有办法在 clojure future 结束时收到通知？

Question

有没有办法对 future 设置监视，以便在完成时触发回调？

类似这样的东西吗？

> (def a (future (Thread/sleep 1000) "Hello World!")
> (when-done a (println @a))

...waits for 1sec...
;; =>  "Hello World"

Answer 1

您可以启动另一个任务来观察 future ，然后运行该函数。在这种情况下，我将使用另一个 future。这很好地包裹在一个完成后的函数中:

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