Pipe dreams aren’t necessarily made of promises

unsorted — cgrand, 2 April 2010 @ 14 h 31 min

Because of the spinning nature of atoms, it’s kind of a hack (a fun hack but still a hack) to build queues on it. Here is the same pipe function built on Java queues:

(defn pipe []
  (let [q (java.util.concurrent.LinkedBlockingQueue.)
        EOQ (Object.)
        NIL (Object.)
        s (fn s [] (lazy-seq (let [x (.take q)] 
                               (when-not (= EOQ x) 
                                 (cons (when-not (= NIL x) x) (s))))))]
    [(s) (fn ([] (.put q EOQ)) ([x] (.put q (or x NIL))))]))

18 Comments »

  1. [...] follow-up: pipe dreams aren’t necessarily made of promises [...]

  2. Thanks again Christophe.

    Comment by Edmund — 2 April 2010 @ 16 h 10 min
  3. why did you decide to return a vector instead of a list?

    Comment by William Hidden — 2 April 2010 @ 16 h 38 min
  4. Nice. It took me a moment to understand the purpose of the NIL object, until I found that LinkedBlockingQueue.put won’t accept a null pointer.

    Comment by Stuart — 2 April 2010 @ 16 h 48 min
  5. J’y comprends toujours rien… mais la “spinning nature of atoms” ? Clojure sert à programmer des ordinateurs quantiques ?

    Comment by Olivier — 2 April 2010 @ 17 h 24 min
  6. @Olivier: un atome Clojure est une référence mutable synchrone non coordonnée (ne participe pas à une transaction) qui est basée sur une opération CAS. Le CAS pouvant échouer, la fonction de mise à jour peut être appliquée plusieurs fois : c’est ça la spinning nature of atoms ! Et oui en écrivant ceci je trouvais ça quantiquement drôle.

    Comment by cgrand — 3 April 2010 @ 20 h 08 min
  7. @William: In Clojure vectors are preferred over lists in such cases.

    Comment by Meikel — 8 April 2010 @ 10 h 03 min
  8. [...] input. I needed to convert input to a more sanitary thing, and so lifted a page directly from the CGrand Master himself. In that post he shows how to create a LinkedBlockingQueue (henceforth LBQ to save pixels), [...]

  9. Note that the implementation above will OutOfMemoryError if large sets of values and/or large values are written into the pipe. Here’s a version that caps the queue that seems to do a better job:

    (defn pipe2
    “Returns a pair: a seq (the read end) and a function (the write end).
    The function can take either no arguments to close the pipe
    or one argument which is appended to the seq. Reads and writes may block.
    The (optional) argument to pipe2 is the maximum size of the queue (beyond
    that size writes will block) – default value if not provided is 100.”
    ([] (pipe2 100))
    ([size]
    (let [q (java.util.concurrent.LinkedBlockingQueue. size)
    EOQ (Object.)
    NIL (Object.)
    s (fn s [] (lazy-seq (let [x (.take q)]
    (when-not (= EOQ x)
    (cons (when-not (= NIL x) x) (s))))))]
    [(s) (fn ([] (.put q EOQ)) ([x] (.put q (or x NIL))))])))

    Test code:

    (let [[q f] (pipe2)]
    (future (doseq [x q] (println x)) (println “that’s all folks!”))
    (doseq [x (range 1000000000)] (f x))
    (f))

    Note: I’m a Clojure n00b, so this may introduce other issues (e.g. deadlock if the queue is full and the readers are also writers).

    Comment by Peter Monks — 8 January 2013 @ 7 h 58 min
  10. [...] read Paul Ingles post “From Callbacks to Sequences” which led me to Christophe Grand’s handy pipe function. The pipe function gives you two things wrapped in a vector: a sequence to pass on for downstream [...]

    Pingback by Pithering About » Pmap styled pipes — 9 February 2013 @ 16 h 34 min
  11. stamps machine

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by stamps machine — 18 November 2014 @ 15 h 09 min
  12. Pure & Easy Slim Reviews

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by Pure & Easy Slim Reviews — 19 November 2014 @ 13 h 12 min
  13. sma pcb Sma Plug

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by sma pcb Sma Plug — 19 November 2014 @ 19 h 16 min
  14. Velour Skin Reviews

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by Velour Skin Reviews — 20 November 2014 @ 7 h 32 min
  15. muscle building pills Review

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by muscle building pills Review — 21 November 2014 @ 12 h 27 min
  16. Wonderful beat ! I wish to apprentice while you amend your
    website, how can i subscribe for a blog website?

    The account aided me a acceptable deal. I had been tiny
    bit acquainted of this your broadcast provided bright clear concept

  17. Hence, in the event of a simple error, we can say that most people do not come into direct contact with him.
    Tesla key generator could also be taken care of
    by attending green electric soltuions a trade school to ensure that a person who earned knowledge through
    various of assignments.

    Comment by Gforce san diego electric company — 6 December 2014 @ 12 h 20 min
  18. Nulexa

    Clojure and me » Pipe dreams aren’t necessarily made of promises

    Trackback by Nulexa — 17 December 2014 @ 9 h 52 min

RSS feed for comments on this post. TrackBack URI

Leave a comment

(c) 2014 Clojure and me | powered by WordPress with Barecity