with-monitor.clj

(defmacro with-monitor
  "Yields an object and a fn to tell if the object has been GC'd yet

  The infinite loop (alive-fn) will quit when the return value (monitor) is no longer referenced and GC is run

  (with-monitor [monitor alive?]
    (let [alive-fn (fn [] (loop []
                            (println \"alive...\")
                            (java.lang.Thread/sleep 1000)
                            (when (alive?) (recur))))]
      (future (alive-fn))
      monitor))"
    [[tracer-binding alive?-fn-binding] & body]
  `(let [~tracer-binding (Object.)
        weak-ref# (java.lang.ref.WeakReference. ~tracer-binding)
        ~alive?-fn-binding (fn [] (not (nil? (.get weak-ref#))))]
    ~@body))