interface - 当可调用是 Clojure 函数时，从 ScheduledFutureTask 获取 nil 而不是返回值

Question

我正在尝试使用 Executors.newSingleThreadScheduledExecutor() 来安排 Clojure 函数。令人烦恼的是，在生成的 ScheduledFutureTask 上调用 .get() 返回 nil 而不是函数的结果。

我以希基先生对 future 的实现为模型。

(ns my.ns
    (:import (java.util.concurrent Executors ThreadFactory TimeUnit)))


(def ^:private thread-pool-scheduler (atom nil))


(def ^:private thread-pool-counter (agent 0))

(defn- get-and-increment-thread-id []
   (-> thread-pool-counter (send inc) deref))

(def ^:private thread-factory 
    (reify ThreadFactory 
     (newThread [this f]
        (let [thread (Thread. f)]
          (.setName thread (format "clojure-scheduled-future-thread-pool-%d"
                       (get-and-increment-thread-id)))
          thread))))

(defn scheduled-future-call [^Callable f ^long delay ^TimeUnit unit]
    (.schedule (scheduled-futures-executor) (bound-fn* f) delay unit))

(defn start-scheduled-futures-executor! []
    (reset! thread-pool-scheduler
    (Executors/newSingleThreadScheduledExecutor thread-factory)))

(defn scheduled-futures-executor []
    (or @thread-pool-scheduler
        (start-scheduled-futures-executor!)))

一切正常，并在适当的时候触发副作用(例如调度 #(println "ok"))。
但是，调用生成的 ScheduledFutureTask 的 get() 方法总是给我 nil
(例如调度 #(+ 5 5))。

我尝试显式扩展 Callable，尝试省略 bound-fn*，但结果是一样的:

(defprotocol ISchedule
    (schedule [this delay time-unit]))

(extend Callable
    ISchedule
    {:schedule (fn [this delay time-unit]
       (.schedule (scheduled-futures-executor) this delay time-unit))})

我的直觉是 ScheduledExecutorService 选择 schedule(Runnable, long, TimeUnit) 而不是 schedule(Callable, long, TimeUnit)，但不应该输入提示来解决这个问题吗？

非常非常感谢您的帮助或提示!

Answer 1

My intuition is that the ScheduledExecutorService is choosing schedule(Runnable, long, TimeUnit) over schedule(Callable, long, TimeUnit),

我认为你是对的，只有我具体化了 Callable它工作正常。 (我还在 import 语句的类列表中添加了 Callable)。

编辑:我还删除了对 bound-fn* 的调用

一探究竟:

(defn make-callable [f] (reify Callable (call [this] (f))))

(def cat (make-callable (fn [] (println "meeow") "i am a cat")))

(def who-are-you? (scheduled-future-call cat 2 TimeUnit/SECONDS))

(println "Tell me who you are!\n\t" (.get who-are-you?))

输出:

meeow
Tell me who you are!
    i am a cat