Ok, looks like ##resolve-referencing-objects is in place now!
> (define a "Hello world")
> (##resolve-referencing-objects a)
(#<absent> #<absent> #<absent>)
> (list a)
("Hello world")
> (##resolve-referencing-objects a)
(#<absent> #<absent> #<absent> ("Hello world"))
> (vector a)
#("Hello world")
> (##resolve-referencing-objects a)
(#<absent> #<absent> #<absent> #("Hello world") ("Hello world"))
> 0 1 2
0
> 1
> 2
> (##gc)
> (##resolve-referencing-objects a)
(#<absent> #<absent> #<absent>)
Implementation:
To _kernel.scm row 4388 and on are added:
;;;----------------------------------------------------------------------------
;;; Resolver of referencing objects
;;; Works for memory-allocated objects only, for details see the conditions for
;;; the validate_old_obj call in mem.c .
; For this procedure to work, up to the point where the explicitly induced GC is made,
; there must be no other GC.
;
; (##resolve-referencing-objects obj) => list of the objects that reference obj
(define (##resolve-referencing-objects obj)
(##declare (not interrupts-enabled))
; Set the object to scan for
(##c-code #<<end-of-code
// Note that this variable is declared even if the referencing objects resolver
// is not enabled.
resolve_objects_referencing = ___ARG1;
end-of-code
obj)
; Trig garbage collection as to perform the scan
(##gc)
; Reset the object to scan for setting
(##c-code #<<end-of-code
resolve_objects_referencing = -1;
end-of-code
)
; Simplistic way of indicating to user whether this procedure is implemented.
(and (##c-code #<<end-of-code
#ifdef ___DEBUG
___RESULT = ___TRU;
#else
___RESULT = ___FAL;
#endif
end-of-code
)
; Download the resolved objects and return
(let loop ((r '()))
(let ((object (##c-code "___RESULT = get_next_resolved_referencing_object();")))
(if object
(loop (cons object r))
r)))))
To mem.h row 69 and on are added:
extern ___SCMOBJ resolve_objects_referencing;
extern ___SCMOBJ get_next_resolved_referencing_object ___PVOID;
To mem.h are added starting at the following rows:
30:
/*
* Defining the symbol ENABLE_REFERENCING_OBJECTS_RESOLVER will enable
* the GC to resolve the references to a specified object, see
* ##resolve-referencing-objects of _kernel.scm for more info.
*/
#define ENABLE_REFERENCING_OBJECTS_RESOLVER
423:
/* Object to look up all references to */
___WORD resolve_objects_referencing = -1;
typedef struct resolved_referencing_object_struct {
___SCMOBJ object;
struct resolved_referencing_object_struct* next;
} resolved_referencing_object;
___HIDDEN resolved_referencing_object* resolved_referencing_objects = NULL;
void add_resolved_referencing_object(___SCMOBJ object) {
resolved_referencing_object* r = (resolved_referencing_object*) malloc(sizeof(resolved_referencing_object));
r->object = object;
r->next = resolved_referencing_objects;
resolved_referencing_objects = r;
}
// Get next object resolved as referencing resolve_objects_referencing .
// Used by ##resolve-referencing-objects
___SCMOBJ get_next_resolved_referencing_object ___PVOID
{
if (resolved_referencing_objects == NULL) {
return ___FAL;
} else {
resolved_referencing_object* r = resolved_referencing_objects;
___SCMOBJ object = r->object;
resolved_referencing_objects = r->next;
free(r);
return object;
}
}
2184 (replacing the previous ifdef-endif validate_old_obj block):
#if defined(ENABLE_CONSISTENCY_CHECKS) || defined(ENABLE_REFERENCING_OBJECTS_RESOLVER)
#ifdef ENABLE_REFERENCING_OBJECTS_RESOLVER
if (obj == resolve_objects_referencing) {
// This typecasting of container_body to ___SCMOBJ was inspired by the corresponding code in explain_problem .
if (reference_location == IN_OBJECT) {
// Reference from other Scheme object's body
___WORD container;
#if ___tPAIR != ___tSUBTYPED
___WORD head = container_body[-1];
int subtype = ___HD_SUBTYPE(head);
if (subtype == ___sPAIR)
container = ___TAG(container_body-___BODY_OFS,___tPAIR);
else
#endif
container = ___TAG(container_body-___BODY_OFS,___tSUBTYPED);
// ___printf("Found match to sought for object %lu : ",resolve_objects_referencing);
// print_object(container,0,"",0);
// ___printf("\n");
add_resolved_referencing_object(container);
} else {
// Reference from global variable etc.
add_resolved_referencing_object(___ABSENT);
}
}
#endif
#ifdef ENABLE_CONSISTENCY_CHECKS
if (___DEBUG_SETTINGS_LEVEL(___setup_params.debug_settings) >= 1)
validate_old_obj (obj);
#endif
#endif
and the #define ENABLE_CONSISTENCY_CHECKS :s that regard a block that define or set reference_location are replaced with #if defined(ENABLE_CONSISTENCY_CHECKS) || defined(ENABLE_REFERENCING_OBJECTS_RESOLVER) .
Compilation of a new ./gsc/gsc (g++):
cd lib
g++ -Wno-unused -Wno-write-strings -g -fno-trapping-math -fno-strict-aliasing -fwrapv -fPIC -fno-common -mieee-fp -I"../include" -c -o "mem.o" -I. -DHAVE_CONFIG_H -D___GAMBCDIR="\"/usr/local/Gambit-C\"" -D___SYS_TYPE_CPU="\"i686\"" -D___SYS_TYPE_VENDOR="\"pc\"" -D___SYS_TYPE_OS="\"linux-gnu\"" -D___CONFIGURE_COMMAND="\"./configure '--enable-cplusplus' '--enable-single-host' '--enable-debug'"\" -D___OBJ_EXTENSION="\".o\"" -D___EXE_EXTENSION="\"\"" -D___BAT_EXTENSION="\"\"" -D___PRIMAL mem.c -D___LIBRARY
gsc -:~~bin=../bin,~~lib=../lib,~~include=../include -c _kernel.scm
gsc -:~~bin=../bin,~~lib=../lib,~~include=../include -f -link -flat -o _gambc.c _kernel.c _system.c _num.c _std.c _eval.c _io.c _nonstd.c _thread.c _repl.c
g++ -Wno-unused -Wno-write-strings -g -fno-trapping-math -fno-strict-aliasing -fwrapv -fPIC -fno-common -mieee-fp -I"../include" -c -o "_kernel.o" -I. -DHAVE_CONFIG_H -D___GAMBCDIR="\"/usr/local/Gambit-C\"" -D___SYS_TYPE_CPU="\"i686\"" -D___SYS_TYPE_VENDOR="\"pc\"" -D___SYS_TYPE_OS="\"linux-gnu\"" -D___CONFIGURE_COMMAND="\"./configure '--enable-cplusplus' '--enable-single-host' '--enable-debug'"\" -D___OBJ_EXTENSION="\".o\"" -D___EXE_EXTENSION="\"\"" -D___BAT_EXTENSION="\"\"" -D___PRIMAL _kernel.c -D___LIBRARY
cd ..
make
Space for improvement or things to note are:
* ##resolve-referencing-objects is always compiled, but returns #f if Gambit is not compiled with --enable-debug .
Possibly some neater or otherwise better degradation of the procedure could be devised for when Gambit is not compiled in debug mode?
* When compiled with --debug, on the iteration over each memory-allocated object, two checks are always done, namely the two highlighted above.
These could easily be united to one collective check, by making a global boolean variable sth like perform_individual_object_checks that's set to (resolve_objects_referencing != -1) || (___DEBUG_SETTINGS_LEVEL(___setup_params.debug_settings) >= 1) on ___garbage_collect .
Those two checks would then be surrounded by if (perform_individual_object_checks) { .. } .
This would save some clock cycles in the ordinary use case, but add ~5 lines of complexity to mem.c .
* Note that object references that are from objects other than Gambit standard objects, are represented as an absent special object.
* I did not implement this in validate_old_obj as ##resolve-referencing-objects is quite common to use
and validate_old_obj in contrast looks like a very expensive, special-purpose routine.
Feedback?
Mikael
2013/6/18 Marc Feeley
<feeley@iro.umontreal.ca>
Also, your code would be useful to others, so please do a pull request when you are done.
Marc
On Jun 18, 2013, at 12:00 PM, Mikael <
mikael.rcv@gmail.com> wrote:
> Ah, yey, your code in explain_problem already provided an example of how to do this!
>
> Will write here soon how to do this lookup of referencing objects soon.
>