asynchronous - 如何确保所有数据都从 clojure core.async channel 写入文件？

Question

我对 core.async 很陌生，我一直在尝试了解如何最好地使用 core.async 和文件 IO。我整理了一个测试，尽管打印到控制台有效，但无法写入最后一个文件。知道我缺少什么吗？

首先，一些功能...

(defn thread-write-to-files [channel]
  (let [writer (atom nil)]
    (thread
      (loop []
        (when-some [value (<!! channel)]
          (if (and (map? value) (= :FILE (:type value)))
            (do (when @writer (.close ^Writer @writer))
                (reset! writer (io/writer (File. ^String (:name value))))
                (recur))
            (do (when @writer (.write @writer value)
                              (println value))
                (recur)))))
      (when @writer
        (do (.flush @writer)
            (.close ^Writer @writer))))))

(defn add-line-number [channel-in channel-out]
  (go-loop [line-number 1]
    (when-some [value (<! channel-in)]
      (if (and (map? value) (= :FILE (:type value)))
        (do (>! channel-out value)
            (recur 1))
        (do (>! channel-out (str line-number ". " value))
            (recur (inc line-number)))))))

现在一个使用它们的测试......

(deftest test-thread-write-to-file
  (let [input-coll ["This gets skipped"
                   {:type :FILE :name "foo.txt"}
                   "This is the first line of foo!\n"
                   "This is the second line of foo.\n"
                   {:type :FILE :name "bar.txt"}
                   "Bar me 1.\n"
                   "Bar me 2.\n"
                   "Bar me 3.\n"
                   {:type :FILE :name "baz.txt"}
                   "BBBBBBBBBBB\n"
                   "AAAAAAAAAAA\n"
                   "ZZZZZZZZZZZ\n"]
        input-channel (async/to-chan input-coll)
        output-channel (chan)
        foo (File. "foo.txt")
        bar (File. "bar.txt")
        baz (File. "baz.txt")]
    (when (.exists foo) (.delete foo))
    (when (.exists bar) (.delete bar))
    (when (.exists baz) (.delete baz))
    (add-line-number input-channel output-channel)
    (thread-write-to-files output-channel)
    (Thread/sleep 1000)
    (is (.exists foo))
    (is (.exists bar))
    (is (.exists baz))
    (is (> (.length foo) 0))
    (is (> (.length bar) 0))
    (is (> (.length baz) 0))))

测试的最后一个条件失败。文件 baz.txt 已创建，但为空。我的 REPL 从输入中打印出每一行，所以我很困惑为什么文件仍然是空的。

Answer 1

在 thread-write-to-files当输入 channel 关闭时(当 (when-some [value (<!! channel)] ...) 为 nil 并退出 loop 时)，您执行最终文件的刷新和关闭。
您的测试永远不会关闭 channel ，因此不会发生这种情况。尝试使用 close!在 output-channel , 或者使用 onto-chan 而不是 to-chan将测试数据收集到系统中。