I'm Cc-ing cffi-devel and sbcl-devel, since I'm sure more people will
be interested in this and hopefully others will help in figuring this
out.
On 2005-dec-31, at 13:59, Thomas F. Burdick wrote:
I noticed in the #lisp logs that you're having problems preserving
callbacks across image saves. SBCL already goes to quite a bit of
effort to make sure this works. From C's point of view, the callbacks
will never move. But because your library is in lisp, and persists
across image saves, from its point of view, callback objects can move
at arbitrary times. Instead of storing SAPs, you should store the
alien-value object that alien-lambda returns. If you actually need
the SAP, get it only when you need it, using alien-sap.
We're not even testing if the callback moves or not. Our libtest is
not saving the callbacks' address.
Here's the a testcase, using sb-alien (sort of):
[EMAIL PROTECTED]:/tmp$ cat sbcl-callback.lisp
(use-package :sb-alien)
(define-alien-routine "qsort" void
(base system-area-pointer)
(nmemb int)
(size int)
(compar system-area-pointer))
(defparameter *callback*
(sb-alien::alien-lambda int
((a system-area-pointer) (b system-area-pointer))
(let ((x (sb-sys:signed-sap-ref-32 a 0))
(y (sb-sys:signed-sap-ref-32 b 0)))
(cond ((> x y) 1)
((< x y) -1)
(t 0)))))
(defun test ()
(let ((array (alien-sap (make-alien (unsigned 32) 10))))
(dotimes (i 10)
(setf (sb-sys:signed-sap-ref-32 array (* i 4))
(nth i '(7 2 8 9 6 1 10 3 5 4))))
(qsort array 10 4 (alien-sap *callback*))
(dotimes (i 10)
(format t "~A " (sb-sys:signed-sap-ref-32 array (* i 4))))
(free-alien (sap-alien array (* (unsigned 32))))))
[EMAIL PROTECTED]:/tmp$ sbcl --sysinit /dev/null --userinit /dev/null
This is SBCL 0.9.8.3, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.
SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses. See the CREDITS and COPYING files in the
distribution for more information.
* (load "sbcl-callback.lisp")
T
* (test)
1 2 3 4 5 6 7 8 9 10
NIL
* (sb-ext:save-lisp-and-die "test.core")
[undoing binding stack and other enclosing state... done]
[saving current Lisp image into /tmp/test.core:
writing 1584 bytes from the read-only space at 0x01000000
writing 1368 bytes from the static space at 0x05000000
writing 22609920 bytes from the dynamic space at 0x09000000
done]
[EMAIL PROTECTED]:/tmp$ sbcl --core test.core
This is SBCL 0.9.8.3, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.
SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses. See the CREDITS and COPYING files in the
distribution for more information.
* (test)
debugger invoked on a SB-KERNEL::MEMORY-FAULT-ERROR: memory fault
Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.
restarts (invokable by number or by possibly-abbreviated name):
0: [ABORT] Exit debugger, returning to top level.
(SB-KERNEL::MEMORY-FAULT-ERROR)
0]
Any pointers? Well, I'm off to party. Happy new year!
--
Luís Oliveira
http://student.dei.uc.pt/~lmoliv/
Equipa Portuguesa do Translation Project
http://www.iro.umontreal.ca/translation/registry.cgi?team=pt
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