Here is working example code demonstrating how you might do this without
agents:
(in-ns 'user)
(def tasks (ref (into clojure.lang.PersistentQueue/EMPTY (range 1 1000))))
(defn get-task
[tasks]
(dosync
(let [task (first @tasks)]
(alter tasks pop)
task)))
(defn worker-loop
[]
(loop [completed-tasks []]
(if-let [task (get-task tasks)]
(recur (conj completed-tasks task))
completed-tasks)))
(defn create-workers
[n & options]
(vec (repeatedly n (fn []
(future
(worker-loop))))))
(def workers
(create-workers 100))
(defn worker-test
[xs]
(= (set (mapcat deref workers))
(set xs)))
(worker-test (range 1 1000))
On Tuesday, August 23, 2016 at 9:09:31 AM UTC-4, adrian...@mail.yu.edu
wrote:
>
> I haven't run your code yet, but it's bad form to use Clojure's reference
> types inside other reference types. They should store persistent data
> structures to really make any sense in a concurrent context.
>
> On Tuesday, August 23, 2016 at 8:22:00 AM UTC-4, Sergei Koledov wrote:
>>
>> Hello,
>>
>> I had a problem when I run the following code:
>>
>> (defn get-task [tasks]
>> (dosync
>> (let [task (first @tasks)]
>> (alter tasks rest)
>> task)))
>>
>> (defn worker [& {:keys [tasks]}]
>> (agent {:tasks tasks}))
>>
>> (defn worker-loop [{:keys [tasks] :as state}]
>> (loop [last-task nil]
>> (if-let [task (get-task tasks)]
>> (recur task)
>> (locking :out (println "Last task: " last-task))))
>> state)
>>
>> (defn create-workers [count & options]
>> (->> (range 0 count)
>> (map (fn [_] (apply worker options)))
>> (into [])))
>>
>> (defn start-workers [workers]
>> (doseq [worker workers] (send-off worker worker-loop)))
>>
>> (def tasks (ref (range 1 10000000)))
>>
>> (def workers (create-workers 100 :tasks tasks))
>>
>> (start-workers workers)
>> (apply await workers)
>>
>> Description: I have several agents (100 in my case). Each agent running
>> in a separate thread. All agents share the one ref with the collection of
>> tasks (range of longs in my case). Each agent get tasks from the collection
>> (in transaction) one by one until the collection becomes empty and then
>> prints the last task which it handle. However, when I run this code it
>> looks like the collection of tasks suddenly becomes empty and workers
>> handle only portion of all tasks (average 25-40% of all number).
>>
>> This code behave as I expected, when I create only one agent or use
>> explicit locking in get-task function:
>>
>> (defn get-task [tasks]
>> (locking :lock
>> (dosync
>> (let [task (first @tasks)]
>> (alter tasks rest)
>> task))))
>>
>> I run this code on the Clojure 1.8.0
>> java version "1.8.0_91"
>> Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
>> Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)
>>
>> Can anyone tell me, what am I doing wrong, or it really looks like a bug
>> in the clojure STM?
>> I already asked this question on stackoverflow.com (
>> http://stackoverflow.com/questions/39054911/strange-behavior-of-clojure-ref),
>>
>> but so far nobody has been able to help me.
>>
>> P.S. Sorry for my english skill.
>>
>
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