Simplify and extend using the knots exception with stack

knots/thread-pool.scm

@@ -253,18 +253,20 @@ arguments of the thread pool procedure."
                                            proc)
                               (with-exception-handler
                                   (lambda (exn)
-                                    (when (log-exception? exn)
-                                      (simple-format
-                                       (current-error-port)
-                                       "thread-pool: exception running ~A\n" proc)
-                                      (print-backtrace-and-exception/knots
-                                       exn))
-                                    (raise-exception exn))
+                                    (match (fluid-ref %stacks)
+                                      ((stack-tag . prompt-tag)
+                                       (let ((stack (make-stack #t
+                                                                0 prompt-tag
+                                                                0 (and prompt-tag 1))))
+                                         (raise-exception
+                                          (make-exception
+                                           exn
+                                           (make-knots-exception stack)))))))
                                 (lambda ()
                                   (call-with-values
                                       (lambda ()
                                         (start-stack
-                                         'thread-pool
+                                         #t
                                          (apply proc args)))
                                     (lambda vals
                                       (cons (/ (- (get-internal-real-time)