crashes with Fibers

["Clément Lassieur" <clement@lassieur.org>]

Hi,

I'm encountering a few crashes with Fibers that happen when I call
CALL-WITH-NEW-THREAD in a Fiber.  TEST4 crashes every time.  TEST5 never
outputs, but it doesn't crash every time.

TEST1 is exactly like TEST5 except that I replace CALL-WITH-NEW-THREAD
with SPAWN-FIBER.

Is it a mistake from me or a Guile bug?  If it is a bug, do you know if
there are workarounds?

Thank you,
Clément

    (use-modules (fibers channels)
                 (fibers))

    ;; good
    (define (test1)
      (run-fibers
       (lambda ()
         (spawn-fiber
          (lambda ()
            (let ((channel (make-channel)))
              (spawn-fiber
               (lambda ()
                 (put-message channel "hello world")))
              (format #t "~a~%" (get-message channel))))))
       #:drain? #t))
    ⊣ hello world

    ;; good
    (define (test2)
      (let ((channel (make-channel)))
        (call-with-new-thread
         (lambda ()
           (put-message channel "hello world")))
        (format #t "~a~%" (get-message channel))))
    ⊣ hello world
    ⇒ #t

    ;; good
    (define (test3)
      (run-fibers
       (lambda ()
         (let ((channel (make-channel)))
           (call-with-new-thread
            (lambda ()
              (put-message channel "hello world")))
           (format #t "~a~%" (get-message channel))))
       #:drain? #t))
    ⊣ hello world
    ⇒ #t

    ;; bad
    (define (test4)
      (run-fibers
       (lambda ()
         (spawn-fiber
          (lambda ()
            (let ((channel (make-channel)))
              (call-with-new-thread
               (lambda ()
                 (put-message channel "hello world")))))))
       #:drain? #t))
    ⊣ scheme@(guile-user)> In /home/clement/.guix-profile/share/guile/site/2.2/fibers/internal.scm:
          402:6  1 (suspend-current-fiber _)
      In unknown file:
                 0 (scm-error misc-error #f "~A" ("Attempt to suspend fiber within continuation barrier") #f)
      ERROR: In procedure scm-error:
      Attempt to suspend fiber within continuation barrier

    ;; bad
    (define (test5)
      (run-fibers
       (lambda ()
         (spawn-fiber
          (lambda ()
            (let ((channel (make-channel)))
              (call-with-new-thread
               (lambda ()
                 (put-message channel "hello world")))
              (format #t "~a~%" (get-message channel))))))
       #:drain? #t))
    ⊣ scheme@(guile-user)> In /home/clement/.guix-profile/share/guile/site/2.2/fibers/operations.scm:
          188:5  3 (perform-operation #<<base-op> wrap-fn: #f try-fn: #<procedure try-fn ()> block-fn: #<procedure block-fn (put-flag put-sched resume-put)>>)
      In /home/clement/.guix-profile/share/guile/site/2.2/fibers/channels.scm:
          88:26  2 (try-fn)
      In /home/clement/.guix-profile/share/guile/site/2.2/fibers/internal.scm:
          219:6  1 (schedule-fiber! _ _)
      In unknown file:
                 0 (scm-error misc-error #f "~A" ("epoll instance is dead") #f)
      ERROR: In procedure scm-error:
      epoll instance is dead