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POWhy does Clojure hang after having performed my calculations?
 

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  1. POWhy does Clojure hang after having performed my calculations?
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    <p>I'm experimenting with filtering through elements in parallel. For each element, I need to perform a distance calculation to see if it is close enough to a target point. Never mind that data structures already exist for doing this, I'm just doing initial experiments for now.</p> <p>Anyway, I wanted to run some very basic experiments where I generate random vectors and filter them. Here's my implementation that does all of this</p> <pre><code>(defn pfilter [pred coll] (map second (filter first (pmap (fn [item] [(pred item) item]) coll)))) (defn random-n-vector [n] (take n (repeatedly rand))) (defn distance [u v] (Math/sqrt (reduce + (map #(Math/pow (- %1 %2) 2) u v)))) (defn -main [&amp; args] (let [[n-str vectors-str threshold-str] args n (Integer/parseInt n-str) vectors (Integer/parseInt vectors-str) threshold (Double/parseDouble threshold-str) random-vector (partial random-n-vector n) u (random-vector)] (time (println n vectors (count (pfilter (fn [v] (&lt; (distance u v) threshold)) (take vectors (repeatedly random-vector)))))))) </code></pre> <p>The code executes and returns what I expect, that is the parameter n (length of vectors), vectors (the number of vectors) and the number of vectors that are closer than a threshold to the target vector. What I don't understand is why the programs hangs for an additional minute before terminating.</p> <p>Here is the output of a run which demonstrates the error</p> <pre> $ time lein run 10 100000 1.0 [null] 10 100000 12283 [null] "Elapsed time: 3300.856 msecs" real 1m6.336s user 0m7.204s sys 0m1.495s </pre> <p>Any comments on how to filter in parallel in general are also more than welcome, as I haven't yet confirmed that <code>pfilter</code> actually works.</p>
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