How to lock up core.async

gistfile1.clj

(import '[java.util.concurrent CountDownLatch])
(require '[clojure.core.async :as async])

(defn now []
  (System/currentTimeMillis))

(defn waiter [i latch results]
  (async/go
    (swap! results conj [i :waiting (now)])
    (.await latch) ;; Will block the thread
    (swap! results conj [i :done (now)])))

(def core-async-thread-count (-> (Runtime/getRuntime) (.availableProcessors) (* 2) (+ 42)))
(def x (+ core-async-thread-count 1))

(defn- parse-results [results]
  (->> @results 
       (group-by second)
       (map (fn [[k v]] [k (count v)]))
       (into {})))

(defn show-bug []
  (let [latch (CountDownLatch. 1)
        results (atom [])]
    (dotimes [i x] (waiter i latch results))

    (let [parsed (parse-results results)]
      (if (= x (:waiting parsed))
        (println "no lockup!")
        (println "Expected" x "to be waiting, but there were" parsed)))))

(show-bug)