我试图使用clojure core.async通道来节省内存密集型并发进程 . 每个进程将图像加载到内存中并应用水印 . 如果我尝试同时处理太多图像,我会收到OOM错误 .
下面的模式似乎有效,但感觉有点不雅 . 我的问题是,使用core.async有更好的方法吗?或者,我应该只使用java并发的东西来做这件事(即创建一个固定大小的线程池等) .
下面的代码中的基本概念是使用全局固定大小的通道, tchan
用于限制进入 in-chan
的内容,基本上将并发进程的数量限制为 tchan
的大小 .
在下面的代码中, process-images
是入口点 .
(def tbuff (buffer 20))
(def tchan
"tchan is used to throttle the number of processes
tbuff is a fixed size buffer"
(chan tbuff))
(defn accum-results
"Accumulates the images in results-chan"
[n result-chan]
(let [chans [result-chan (timeout timeout-ms)]]
(loop [imgs-out []
remaining n]
(if (zero? remaining)
imgs-out
(let [[img-result _] (alts!! chans)]
(if (nil? img-result)
(do
(log/warn "Image processing timed out")
(go (dotimes [_ remaining] (<! tchan)))
imgs-out)
(do
(go (<! tchan))
(recur (conj imgs-out img-result) (dec remaining)))))))))
(defn process-images
"Concurrently watermarks a list of images
Images is a sequence of maps representing image info
Concurrently fetches each actual image and applies the watermark
Returns a map of image info map -> image input stream"
[images]
(let [num-imgs (count images)
in-chan (chan num-imgs)
out-chan (chan num-imgs)]
;; set up the image-map consumer
;; asynchronously process things found on in-chan
(go
(dotimes [_ num-imgs]
; block here on input images
(let [img-in (<! in-chan)]
(thread
(let [img-out (watermark/watermarked-image-is img-in)]
(>!! out-chan [img-in img-out]))))))
;; put images on in-chan
(go
(doseq [img images]
(>! tchan :x)
(>! in-chan img)))
;; accum results
(let [results (accum-results num-imgs out-chan)]
(log/info (format "Processed %s of %s images and tbuff is %s"
(count results) num-imgs (count tbuff)))
(into {} results))))
1 回答
我相信这正是pipeline的用途 .
这是一个例子: