thread ring, clojure core.async style

async_thread_ring.clj

(require '[clojure.core.async :refer [chan go <! <!! >! >!!]])

(defn thread-ring [size n]
  {:pre [(> size 1)]}
  (let [result (chan 1)
        [head :as ring] (vec (repeatedly size #(chan 1)))]
    (dotimes [i size]
      (let [id (inc i)
            in (ring i)
            out (ring (mod id size))]
        (go (while true
              (let [m (<! in)]
                (if (> m 0)
                  (>! out (dec m))
                  (>! result id)))))))
    (>!! head n)
    (<!! result)))

It works, is cute, although 1.5x slower than agent-based thread ring.
https://github.com/clojure/test.benchmark/blob/master/src/main/clojure/alioth/thread_ring.clj

(thanks to Tim Baldridge for r2 change to size 1 channels, ~20% speed improvement)