gistfile1.lisp

(defun return-fastest (&rest functions)
  (let* ((retvals nil)
         (threads nil)
         (results-lock (bt:make-lock "results"))
         (sig (bt:make-condition-variable))
         (wrapped (mapcar (lambda (fn)
                            (lambda ()
                              (let ((got-results (bt:with-lock-held (results-lock) retvals)))
                                (format t "th: res1: ~a~%" got-results)
                                (unless got-results
                                  (let ((local-vals (multiple-value-list (funcall fn))))
                                    (format t "th: comp: ~a~%" local-vals)
                                    (bt:with-lock-held (results-lock)
                                      (format t "th: res2: ~a~%" local-vals)
                                      (unless retvals
                                        (setf retvals local-vals)
                                        (format t "th: setting res, firing sig ~a~%" sig)
                                        (bt:condition-notify sig)
                                        (format t "th: sig fired~%"))))))))
                          functions)))
    (dolist (fn wrapped)
      (format t "starting thread~%")
      (push (bt:make-thread fn) threads))
    (bt:with-lock-held (results-lock)
      (unless retvals
        (format t "waiting on sig ~a~%" sig)
        (bt:condition-wait sig results-lock)))
    (values-list retvals)))

(format t "~%starting...~%")
(let ((res (return-fastest
             (lambda () (sleep 2) (+ 4 5))
             (lambda () (+ 27 84))
             (lambda () (+ 45 23)))))
  (format t "res: ~a~%" res))