Comment 2 for bug 1424031

Test case:
(format t "~a~%" (sb-unix:unix-getpid))

(defun test ()
  (let ((threads
          (loop repeat 15
                collect (sb-thread:make-thread
                         (lambda ()
                           (let ((threads (sb-thread:list-all-threads)))
                             (dotimes (i 100000)
                               (with-output-to-string (stream)
                                 (let ((*print-pretty* nil)
                                       (*print-circle* t))
                                   (princ threads stream))))))))))
    (mapc #'sb-thread:join-thread threads)))