(defmacro write-with-rw-lock ((lock) &body body)
  (let ((locked (gensym)))
    `(let ((,locked nil))
        (unwind-protect
             (progn
               (begin-write ,lock)
               (setf ,locked t)
               (prog1
                   (progn ,@body)
                 (end-write ,lock)
                 (setf ,locked nil)))
          (when ,locked
            (end-write ,lock))))))