(require 'bt-semaphore)

(let ((top-level *standard-output*))
  (bt:make-thread
   (lambda ()
     (load "x.lisp")
     (sleep 0.5)
     (format top-level (f)))
   :name "hello")
  (bt:make-thread
   (lambda ()
     (load "y.lisp")
     (format top-level (f))
     (sleep 1.0)
     (format top-level (f))
     (format top-level "|"))
   :name "setne"))
;; => 211 ;; should be 212

;; x.lisp
(defun f () (format nil "~A" 1))

;; y.lisp
(defun f () (format nil "~A" 2))