On 2004-10-01, at 06:33:17 -0700, Marc Mettes wrote:
> --- Steve Hay <[EMAIL PROTECTED]> wrote:
>
> > Why does the following XS code leak?
> >
> > #include "EXTERN.h"
> > #include "perl.h"
> > #include "XSUB.h"
> >
> > typedef struct {
> > char *buf;
> > } Foo;
> >
> > Foo *FooAlloc(pTHX) {
> > Foo *foo;
> > New(0, foo, 1, Foo);
> > New(0, foo->buf, 1024, char);
> > return foo;
> > }
> >
> > void FooFree(pTHX_ Foo *foo) {
> > Safefree(foo->buf);
> > //Safefree(foo);
> > }
> >
> > MODULE = Foo PACKAGE = Foo
> >
> > void
> > foo()
> > PPCODE:
> > {
> > SV *sv;
> > Foo *foo;
> > sv = NEWSV(0, 0);
> > foo = FooAlloc(aTHX);
> > sv_usepvn(sv, (char *)foo, sizeof *foo);
> > SvPOK_only(sv);
> > SvREADONLY_on(sv);
> > FooFree(aTHX_ foo);
> > SvREFCNT_dec(sv);
> > }
> >
> > The Safefree(foo) is commented out in FooFree() because I believe
> > that sv_usepvn() has reallo()'ed foo and will free() it for me
> > when sv's refcount becomes 0. I tried uncommenting the Safefree
> >(foo) to see if it made any difference, but it still leaks.
> >
> > The leak is easily seen just by building a Foo module out of the
> > above and running
> >
> > perl -Mblib -MFoo -e "<STDIN>; for (1 ..10000) { Foo::foo() }
> > <STDIN>;"
> >
> > If I comment-out the sv_usepvn() call, and accordingly restore the
> > Safefree(foo) once more, then the XSUB doesn't leak.
> >
>
> Are you sure this line it right?
>
> sv_usepvn(sv, (char *)foo, sizeof *foo);
>
> I get 4 for "sizeof *foo" on solaris, which is not nearly
> as much as the 1024 chars malloc'ed for buf.
That line is correct.
"4" is the size of the structure containing the string pointer.
The 1024 byte buffer doesn't matter at all, it's free()'d
separately.
> I have a feeling that a different (probably smaller) size
> is being passed to realloc(), which leaves a chunk of memory
> out there that is probably not freed after SvREFCNT_dec.
Memory allocators keep track of the size of allocated blocks.
You don't pass the number of bytes to free to free(),
or do you? ;-)
> The man page for realloc hints at this (if the size is 0),
> but the whole thing is very subtle.
>
>
> Just guessing ... I've never used sv_usepvn nor realloc for
> that matter, so I could be totally wrong.
>
>
> Marc
--
The universe is all a spin-off of the Big Bang.
