Nick Ing-Simmons wrote:
>Steve Hay <[EMAIL PROTECTED]> writes:
>
>
>>Revised version (attached) now passes the SV itself again. Then I can
>>check that mg->mg_obj == sv after using mg_find() to see if I've found
>>the right MAGIC *. Am I kidding myself here, or does that work OK?
>>
>>
>
>It will work, but adding SV as mg_obj is quite common.
>Only 100% fool proof scheme I can think of is to store the MAGIC *
>back into "your struct" - but then you don't need to use mg_find anyway ;-)
>
[...]
>>Not sure I like that since behaviour when namelen < 0 isn't documented.
>>So I've added an I32 signature member to my struct and check that it has
>>the correct value after retrieving the magic when it is being used later.
>>
>>
>
>If you use the MAGIC * as the "signature" it can't fail ;-)
>
An excellent idea.
So attached is hopefully my final take.
Using sv_magic(), I've dropped the re-use of the SV in the 2nd arg since
(a) I couldn't pull that trick if I actually wanted to use mg_obj for
something else and (b) the subsequent mg_find() call is always
_immediately_ after sv_magic() anyway so no other magic could have been
added. the MAGIC * is then stored within the struct itself. Later on
(and possibly in another part of the code, when mg_find() wouldn't be
"safe"), the pointer stored with the struct is used to verify that the
correct MAGIC * was found.
Using sv_magicext() is even easier since it returns the MAGIC * for us.
Thanks (once again!) for your help.
- Steve
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#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"
typedef struct {
MAGIC *mg;
char *buf;
} Foo;
static Foo *FooAlloc(pTHX);
static void FooFree(pTHX_ Foo *foo);
static int MagicFooFree(pTHX_ SV *sv, MAGIC *mg);
static MGVTBL Foo_vtbl = {
NULL,
NULL,
NULL,
NULL,
MagicFooFree
};
static Foo *FooAlloc(pTHX) {
Foo *foo;
Newz(0, foo, 1, Foo);
Newz(0, foo->buf, 1024, char);
strcpy(foo->buf, "Hello, world.");
return foo;
}
static void FooFree(pTHX_ Foo *foo) {
Safefree(foo->buf);
Safefree(foo);
}
static int MagicFooFree(pTHX_ SV *sv, MAGIC *mg) {
FooFree(aTHX_ (Foo *)mg->mg_ptr);
return 1;
}
MODULE = Foo PACKAGE = Foo
void
magicfoo()
PPCODE:
{
SV *sv;
Foo *foo;
MAGIC *mg;
// Initialise
foo = FooAlloc(aTHX);
sv = NEWSV(0, 0);
sv_magic(sv, NULL, PERL_MAGIC_ext, (char *)foo, 0);
// This mg_find() can't fail since we're doing it straight away.
if (!(mg = mg_find(sv, PERL_MAGIC_ext)))
croak("Can't find new magic");
foo->mg = mg;
mg->mg_virtual = &Foo_vtbl;
SvREADONLY_on(sv);
// Use it. This could be much later in another function, so we
// need to check that mg_find() found the right magic.
if (!(mg = mg_find(sv, PERL_MAGIC_ext)))
croak("Can't find magic");
if (!(foo = (Foo *)(mg->mg_ptr)))
croak("Can't find magic pointer");
if (foo->mg != mg)
croak("Found wrong magic pointer");
//printf("%s\n", foo->buf);
// Clean up
SvREFCNT_dec(sv);
}
void
magicextfoo()
PPCODE:
{
SV *sv;
Foo *foo;
MAGIC *mg;
// Initialise
foo = FooAlloc(aTHX);
sv = NEWSV(0, 0);
if (!(mg = sv_magicext(sv, NULL, PERL_MAGIC_ext, &Foo_vtbl, (char *)foo, 0)))
croak("Can't add magic");
foo->mg = mg;
SvREADONLY_on(sv);
// Use it. This could be much later in another function, so we
// need to check that mg_find() found the right magic.
if (!(mg = mg_find(sv, PERL_MAGIC_ext)))
croak("Can't find magic");
if (!(foo = (Foo *)(mg->mg_ptr)))
croak("Can't find magic pointer");
if (foo->mg != mg)
croak("Found wrong magic pointer");
//printf("%s\n", foo->buf);
// Clean up
SvREFCNT_dec(sv);
}
