Took me a while to get the idea but higher-order channels are brilliant -
that way one ensures a given reply was actually targeted at one's request.
Thanks for the suggestion!
Faux-agents would have the limitation of not being to (reasonably) perform
blocking I/O - which is the point of my sample program.
An improved version:
(require '[clojure.core.async :as async :refer :all])
(import '[java.util.concurrent Executors]
'[java.util.concurrent.locks ReentrantReadWriteLock])
(spit "bar" (apply str (shuffle (range 100))))
(def max-concurrency 4)
(def requests (chan max-concurrency))
;; only ensures exclusive access within the app - not across the OS
;; too lazy to use a FileLock :)
(def lock (ReentrantReadWriteLock.))
(def rw-pool (Executors/newFixedThreadPool max-concurrency))
;; one sends actions to anonymous one-off multiple agents
;; (as opposed to a single, named one), in order to increase concurrency
(dotimes [_ max-concurrency]
(go (loop []
(when-let [request (<! requests)]
(send-via rw-pool (agent nil) (fn [_]
(try
(-> lock .readLock .lock)
(>!! request (seq (slurp
"bar")))
(finally
(-> lock .readLock
.unlock)))))
(recur)))))
(go (loop []
(let [request (chan)
_ (>! requests request)
response (<! request)]
(send-via rw-pool (agent nil) (fn [_]
(try
(-> lock .writeLock .lock)
(spit "bar" (apply str (shuffle
response)))
(finally
(-> lock .writeLock .unlock)))))
(recur))))
As commented, locking is only partially useful (that's why opening the file
might display an empty string at times). Also, don't know what would be the
best way to indicate termination to the second go block...
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