(defn- write-to-file [{:keys [output_] :as data} fname append? self]
  (let [output (force output_)]
    (try
      (with-open [^java.io.BufferedWriter w (io/writer fname :append append?)]
        (.write   w ^String output)
        (.newLine w))

      (catch java.io.IOException e
        (if (:spit-appender/retry? data)
          (throw e) ; Unexpected error
          (do
            (io/make-parents fname)
            (self (assoc data :spit-appender/retry? true))))))))

(defn my-appender [& [{:keys [fname append? locking?]
                       :or   {fname "./timbre-spit.log"
                              append?  true
                              locking? true}}]]
  (have? enc/nblank-str? fname)
  {:enabled? true
   :fn
   (fn self [data]
     (if locking?
       (locking (Object.)
         (write-to-file data fname append? self))
       (write-to-file data fname append? self)))})

(alter-var-root
 (var timbre/spit-appender)
 my-appender)

(timbre/merge-config! {:appenders {:println {:enabled? false}
                                   :spit (my-appender {:fname "/tmp/clojure-sample.out"})}})