segmentation fault: in callback function when using actionlib #251

wkentaro · 2015-02-21T17:11:19Z

When using actionlib and roseus, I had segmentation fault in its callback function, and resolved it by passing arguments to callback function.

I mean, in the sample code:
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/test/fibonacci-server.l

from

(setq s (instance ros::simple-action-server :init
                  "/fibonacci" actionlib_tutorials::FibonacciAction
                  :execute-cb #'fibonacci-execute-cb))

to

(setq  s (instance ros::simple-action-server :init
                  "/fibonacci" actionlib_tutorials::FibonacciAction
                  :execute-cb #'(lambda (server goal) (fibonacci-execute-cb server goal)))

This segmentation fault doesn't always happen, and the sample code has no problem. In my project, however, I had it.

Actually I don't know the fundamental cause but in my case it is resolved with upper change. As reference my change log is:
wkentaro/jsk_apc@ac8dddf#diff-2a23e2389483ccb4c96d7f07ba40062eR58

The text was updated successfully, but these errors were encountered:

garaemon · 2015-02-21T17:34:22Z

To put it simply, you cannot use #'(lambda (...) ...) form in instance because euslisp does not support closure (Technically, you can use deligation pattern for this problem).

In order to understand this issue perfectly, you need to know closure, free variables, let frame, macro expansion. It's a good lesson to understand how software works.

wkentaro · 2015-02-22T03:08:25Z

Thanks to your introduction, I read some documents of these. I think I understood your point.
Does the code #('lambda (...) ...) problem, if I don't intend to use free variables outside (lambda (...) ...) scope?

In the actionlib.l,
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/euslisp/actionlib.l#L233
it uses (funcall exeucte-cb self goal) so :execute-cb #'execute-cb in instance should be okay. However, in my case it raises segmentation fault.
×:execute-cb #'execute-cb
◯ :execute-cb execute-cb◯:execute-cb #'(lambda (server goal) (execute-cb server goal)◯:execute-cb (lambda (server goal) (execute-cb server goal))

garaemon · 2015-02-22T16:05:00Z

Does the code #('lambda (...) ...) problem, if I don't intend to use free variables outside (lambda (...) ...) scope?

It' a deep world of euslisp.

euslisp SHOULD be able to call lambda form without free variables.
euslisp CANNOT call lambda form which can have free variables outside of its parent environment.

It means that euslisp cannot call lambda function which is created in another let form.

On the other hand, euslip can funcall symbol and in that case euslip evaluate the symbol as function when calling funcall (it's a not common lisp standard).
https://github.com/euslisp/EusLisp/blob/master/lisp/c/eval.c#L1072

(funcall #'+ 1 2)
; => 3

(funcall '+ 1 2) 
; => 3

And, euslisp can call closure even if the environment pointed by closure is on stack.

(let ((var 1))
  (let ((f #'(lambda (x) var)))    ; closure include free variable!
    (print (funcall f 100)))) ; call inside of environment 
; => 1
(funcall (let ((var 1)) ; call out side of environment
           (let ((f #'(lambda (x) var)))    ; closure!
             f)) 1)
; => SEGV

garaemon · 2015-02-22T16:07:12Z

(funcall (let ((var 1))
           (let ((lambda '(lambda (x) var)))    ; closure!
             lambda)) 1)
; => undefined variable var!

Because the code is evaluated as

(funcall (eval '(lambda (x) var)) 1)

And when euslisp evaluate the lambda, there is no such variable like var

garaemon · 2015-02-22T16:16:01Z

And let us assume the code like followings:

(let ((a 1)) ;; let-a
  (let ((b 2)) ;; let-b
     (let ((c 3)) ;; let-c
   )))

Stack of environment in euslisp evaluator is:

nest depth	nickname	parent environment
0	global scope	none
1	let-a	global
2	let-b	let-a
3	let-c	let-b

Euslisp can call lambda which created in parent environment.

defun always create lambda in global scope so that you can call defun-ed functions in any let scopes.

However if you have lambda craeted in let-b, you can call it in let-b and let-c scope but you cannot call it in let-a and global scope

garaemon · 2015-02-22T16:33:14Z

This article may help you to understand stack VM.

wkentaro · 2015-02-27T08:44:55Z

Thanks. I got to know some of the characteristics of euslisp and what I should keep in mind when using it.

k-okada · 2015-03-13T22:05:12Z

sorry for super late response, but did you said that
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/test/fibonacci-server.l
does not working? and we need to rewrite as :execute-cb #'(lambda (server goal) (fibonacci-execute-cb server goal) ??

◉ Kei Okada

On Fri, Feb 27, 2015 at 5:44 PM, Kentaro Wada notifications@github.com
wrote:

Thanks. I got to know some of the characteristics of euslisp and what I
should keep in mind when using it.

—
Reply to this email directly or view it on GitHub
#251 (comment)
.

wkentaro · 2015-03-14T04:15:13Z

No, fibonacci-server.l has no problem.
But in my code I had to write as :execute-cb #'(lambda (server goal) (fibonacci-execute-cb server goal).

k-okada · 2015-03-14T07:54:03Z

may be you can write as :execute-cb #'send self :execute-cb,
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/test/listener.l#L28

◉ Kei Okada

On Sat, Mar 14, 2015 at 1:15 PM, Kentaro Wada notifications@github.com
wrote:

No, fibonacci-server.l has no problem.
But in my code I had to write as :execute-cb #'(lambda (server
goal) (fibonacci-execute-cb server goal).

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#251 (comment)
.

wkentaro · 2015-03-19T17:07:04Z

In this code, :execute-cb #'execute-cb raises unexpected error.
(this is why I opened this issue)
wkentaro/jsk_apc@ac8dddf#diff-2a23e2389483ccb4c96d7f07ba40062eR58

and
In this code
:execute-cb #'send self :execute-cb also raise other error message.
It seems that in instance block of ros::simple-action-server we can't use :execute-cb #'send self :execute-cb.
wkentaro/jsk_apc@c583794#diff-92fac444fd3df4007e9776ba5f97ac76R29

garaemon · 2015-06-12T06:32:11Z

self is problem, self cannot be resolved in global scope. the callback is just evaled by eval special form on the top level scope

k-okada · 2015-06-15T05:06:55Z

I see, please describe that on
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/roseus.cpp#L1555
so that we can see that note on
http://euslisp-docs.readthedocs.org/en/latest/roseus/roseus/#rossubscribe >
@wkentaro

◉ Kei Okada

On Fri, Jun 12, 2015 at 3:32 PM, Ryohei Ueda notifications@github.com
wrote:

self is problem, self cannot be resolved in global scope. the callback is
just evaled by eval special form on the top level scope

—
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#251 (comment)
.

wkentaro · 2015-06-15T17:13:02Z

I have never encountered this problem when using subscriber but actionlib.
Is that really impossible to use self in callback function of subscriber, and this is problem?
In that case, I have no idea how to declare subscription using an instance method as callback function.. :(

garaemon · 2015-06-16T01:44:40Z

:execute-cb #'send self ...
This syntax is simply not supported. https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/euslisp/actionlib.l#L338

garaemon · 2015-06-16T01:47:14Z

In subscription callback function, #'send self :foo is evaluated before ros::subscribe is called

wkentaro · 2015-06-16T01:50:15Z

I see, please describe that on
https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/roseus.cpp#L1555
so that we can see that note on
http://euslisp-docs.readthedocs.org/en/latest/roseus/roseus/#rossubscribe >
@wkentaro

I see, so where should I describe about that? @k-okada
It seems that https://github.com/jsk-ros-pkg/jsk_roseus/blob/master/roseus/roseus.cpp#L1555 has nothing to change.

furushchev · 2016-10-23T21:50:05Z

@wkentaro Is this issue solved?

wkentaro mentioned this issue Feb 21, 2015

move2targetのactionlibバージョンを作成する start-jsk/jsk_apc#100

Closed

wkentaro mentioned this issue May 12, 2015

subscriberのcallback関数に引数を与える start-jsk/jsk_apc#476

Closed

furushchev mentioned this issue Nov 26, 2017

calling setq in action server callback never returns #547

Open

furushchev mentioned this issue Sep 20, 2018

Segmentation fault from subscriber defined in dotimes #579

Open

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segmentation fault: in callback function when using actionlib #251

segmentation fault: in callback function when using actionlib #251

wkentaro commented Feb 21, 2015

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k-okada commented Jun 15, 2015

wkentaro commented Jun 15, 2015

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wkentaro commented Jun 16, 2015

furushchev commented Oct 23, 2016

segmentation fault: in callback function when using actionlib #251

segmentation fault: in callback function when using actionlib #251

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wkentaro commented Feb 21, 2015

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wkentaro commented Feb 27, 2015

k-okada commented Mar 13, 2015

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wkentaro commented Mar 19, 2015

garaemon commented Jun 12, 2015

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wkentaro commented Jun 15, 2015

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wkentaro commented Jun 16, 2015

furushchev commented Oct 23, 2016