bug#37066: Using GOOPS #:allocation #:virtual slot option causes stack overflow

bug#37066: Using GOOPS #:allocation #:virtual slot option causes stack overflow

[Jan]

Hi everyone.

I've written the program attached below and it hangs at writing 
"after changing (K): ", computer freezes for a moment and then Guile
throws the following message:

allocate_stack failed: Can't allocate memory
Warning: Unwind-only `stack-overflow' exception; skipping pre-unwind
handler.
allocate_stack failed: Can't allocate memory
Warning: Unwind-only `stack-overflow' exception; skipping pre-unwind
handler.

Guile version: 2.9.3
OS: Devuan ASCII GNU/Linux
Architecture: x86_64

Code:

(define-class <temperature> ()
  (k #:init-value 0
     #:init-keyword #:k
     #:accessor kelvin)

  (c #:accessor celsius
     #:init-keyword #:c
     #:allocation #:virtual
     #:slot-ref (lambda (o)
                  (let ((k (slot-ref o 'k)))
                    (- k 273.15)))
     #:slot-set! (lambda (o c)
                   (slot-set! o 'c c)
                   (slot-set! o 'k (+ 273.15 c)))))

(define (test-virtual-slots)
  (let ((temp1 (make <temperature> #:k 0)))
    (display "Absolute zero(K): ")
    (display (kelvin temp1))
    (newline)
    (display "Absolute zero(C): ")
    (display (celsius temp1))
    (newline)
    (display "After changing (K): ")
    (slot-set! temp1 'c 0)
    (display (kelvin temp1))))

(test-virtual-slots)

I couldn't find any mistake, because I'm a new Guile user, so please
tell me if I'm doing something wrong. Using an example from the manual
(8.5 Illustrating Slot Description) didn't help, because it also throws
a different error, not sure if I hadn't copied everything or if there's
something fundamentally wrong in GOOPS.

The code of the example:

(define-class <my-complex> (<number>)
  ;; True slots use rectangular coordinates
  (r #:init-value 0 #:accessor real-part #:init-keyword #:r)
  (i #:init-value 0 #:accessor imag-part #:init-keyword #:i)
  ;; Virtual slots access do the conversion
  (m #:accessor magnitude #:init-keyword #:magn
     #:allocation #:virtual
     #:slot-ref (lambda (o)
                  (let ((r (slot-ref o ’r)) (i (slot-ref o ’i)))
                    (sqrt (+ (* r r) (* i i)))))
     #:slot-set! (lambda (o m)
                   (let ((a (slot-ref o ’a)))
                     (slot-set! o ’r (* m (cos a)))
                     (slot-set! o ’i (* m (sin a))))))
  (a #:accessor angle #:init-keyword #:angle
     #:allocation #:virtual
     #:slot-ref (lambda (o)
                  (atan (slot-ref o ’i) (slot-ref o ’r)))
     #:slot-set! (lambda(o a)
                   (let ((m (slot-ref o ’m)))
                     (slot-set! o ’r (* m (cos a)))
                     (slot-set! o ’i (* m (sin a)))))))

(define c (make <my-complex> #:r 12 #:i 20))
(slot-set! c ’a 3)
(display "Real part: ")
(display (real-part c))
(newline)
(display "Angle: ")
(display (angle c))
(newline)
(slot-set! c ’i 10)
(set! (real-part c) 1)
(describe c)

The error:

;;; /home/user/Projects/guile/./goops-bug.scm:44:47: warning: possibly
unbound variable `#{\x2019;i}#'
;;; /home/user/Projects/guile/./goops-bug.scm:47:28: warning: possibly
unbound variable `#{\x2019;a}#'
;;; /home/user/Projects/guile/./goops-bug.scm:48:21: warning: possibly
unbound variable `#{\x2019;r}#'
;;; /home/user/Projects/guile/./goops-bug.scm:49:21: warning: possibly
unbound variable `#{\x2019;i}#'
;;; /home/user/Projects/guile/./goops-bug.scm:53:24: warning: possibly
unbound variable `#{\x2019;i}#'
;;; /home/user/Projects/guile/./goops-bug.scm:53:40: warning: possibly
unbound variable `#{\x2019;r}#'
;;; /home/user/Projects/guile/./goops-bug.scm:55:28: warning: possibly
unbound variable `#{\x2019;m}#'
;;; /home/user/Projects/guile/./goops-bug.scm:56:21: warning: possibly
unbound variable `#{\x2019;r}#'
;;; /home/user/Projects/guile/./goops-bug.scm:57:21: warning: possibly
unbound variable `#{\x2019;i}#'
;;; /home/user/Projects/guile/./goops-bug.scm:60:0: warning: possibly
unbound variable `#{\x2019;a}#'
;;; /home/user/Projects/guile/./goops-bug.scm:67:0: warning: possibly
unbound variable `#{\x2019;i}#'
;;;
compiled /home/user/.cache/guile/ccache/3.0-LE-8-4.1/home/user/Projects/guile/goops-bug.scm.go
Backtrace:
           5 (apply-smob/1 #<catch-closure 55db22ad7780>)
In ice-9/boot-9.scm:
    702:2  4 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
    619:8  3 (_ #(#(#<directory (guile-user) 55db22b9d750>)))
In ice-9/boot-9.scm:
   2296:4  2 (save-module-excursion _)
  3816:12  1 (_)
In /home/user/Projects/guile/./goops-bug.scm:
     69:0  0 (_)

/home/user/Projects/guile/./goops-bug.scm:69:0: Unbound variable:
#{\x2019;a}#


The line 69 is the last line of the program.

bug#37066: Using GOOPS #:allocation #:virtual slot option causes stack overflow

[David Pirotte]

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Hello Jan,

> I've written the program attached below and it hangs at writing 
> "after changing (K): ", computer freezes for a moment and then Guile
> throws the following message:
 
> allocate_stack failed: Can't allocate memory
> Warning: Unwind-only `stack-overflow' exception; skipping pre-unwind
> handler.
> ...

This is not goops bug. The problem occurs because you try to set the
value of the virtual slot, something you should never do. Here is a
slightly corrected version of your code:

(define-module (temperature)
  #:use-module (oop goops)

  #:export (<temperature>
            kelvin
            celsius))

(define-class <temperature> ()
  (k #:accessor kelvin
     #:init-keyword #:k
     #:init-value 0)
  (c #:accessor celsius
     #:init-keyword #:c
     #:allocation #:virtual
     #:slot-ref (lambda (o)
                  (- (kelvin o) 273.15))
     #:slot-set! (lambda (o c)
                   (set! (kelvin o) (+ 273.15 c)))))

Then, in a repl:

scheme@(guile-user)> (add-to-load-path "/your/temperature/module/path")
scheme@(guile-user)> ,use (oop goops)
scheme@(guile-user)> ,use (oop goops describe)
scheme@(guile-user)> ,use (temperature)
;;; note: source file ...  newer than compiled ...
;;; ...
scheme@(guile-user)> (make <temperature>)
$2 = #<<temperature> 5604c4614200>
scheme@(guile-user)> (describe $2)
#<<temperature> 5604c4614200> is an instance of class <temperature>
Slots are: 
     k = 0
     c = -273.15
scheme@(guile-user)> (set! (celsius $2) 0)
$3 = 273.15
scheme@(guile-user)> (describe $2)
#<<temperature> 5604c4614200> is an instance of class <temperature>
Slots are: 
     k = 273.15
     c = 0.0

> ... it also throws a different error ...

I didn't look into this manual example code yet, I wanted to get back
to your own example first ...

David

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bug#37066: Using GOOPS #:allocation #:virtual slot option causes stack overflow

[Jan]

Sorry, I sent a private mail, hope this one will be in the right
place.

On Sun, 18 Aug 2019 05:08:53 -0300
David Pirotte <david@altosw.be> wrote:

> This is not goops bug. The problem occurs because you try to set the
> value of the virtual slot, something you should never do.

Thank you for explaining, I understand it now.
I don't think eating the whole CPU and RAM and segmentation fault is a
good default behavior though. If this is a thing one should never do,
shouldn't Guile throw an error, warning or whatever?


Jan