neg-atom.clj

(ns foobar.baz
  (:require [amazonica.core :as aws]
            [amazonica.aws.s3]
            [amazonica.aws.s3transfer :as s3]))

(def pending (atom 0))
(let [ul (s3/upload :bucket-name bucket-name
                    :key s3-upload-path
                    :input-stream input-stream
                    :metadata {:content-length size
                               :content-type content-type}
                    :access-control-list {:grant-permission ["AllUsers" "Read"]})
      listener #(condp = (:event %)
                  :started   (swap! pending inc)
                  :failed    (swap! pending dec)
                  :completed (swap! pending dec)
                  nil        %)]
  ((:add-progress-listener ul) listener))