On Sat, Mar 20, 2010 at 02:56:11PM +0100, Martin Kersten wrote:
> Stefan Manegold wrote:
> > On Sat, Mar 20, 2010 at 12:53:12PM +0000, Martin Kersten wrote:
> >> Update of /cvsroot/monetdb/MonetDB5/src/modules/kernel
> >> In directory sfp-cvsdas-1.v30.ch3.sourceforge.com:/tmp/cvs-serv10537
> >>
> >> Modified Files:
> >> Tag: Feb2010
> >> batcast.mx
> >> Log Message:
> >> Backport of possible dangerous double frees. No roll forward needed.
> >
> > While your revised code looks indeed more efficient to me (as it allows
> > ATOMfromstr() --- well, at least strFromStr(); I cannot tell about other
> > "extern" (varsized) atoms --- to reuse a allocated temporary buffer),
> > I wonder whether/why the original experienced double frees?
> The implicit contract in gdk_atoms is to use v+len, i.e. pass a pre-alloced
> buffer and realloc upon need.
> Just freeing v without resetting it to NULL is bound to give problems
> with larger values becoming stored.
>
> Setting v=NULL would have been the other option.
v was declared as
ptr v = NULL;
with in the look body, and hence should have been initialized with each
iteration, shouldn't it?
Stefan
> > Called with v==NULL,
> > ATOMfromstr() --- again, I refer only to strFromStr(); FromStr functions for
> > other "extern" (varsized) atoms might behave differently; IMHO, we don't
> > have any "contract" or "policies" for FromStr() implementations --- would
> > allocate a buffer for the result,
> > ATOMput() copies the value from the buffer to the BAT heap,
> > and then the buffer is (was) freed.
> >
> > Looks very sound to me.
> >
> > What am I missing?
> >
> > I would be thankful for any enlightment.
> >
> > Stefan
> >
> >> Index: batcast.mx
> >> ===================================================================
> >> RCS file: /cvsroot/monetdb/MonetDB5/src/modules/kernel/batcast.mx,v
> >> retrieving revision 1.31.2.7
> >> retrieving revision 1.31.2.8
> >> diff -u -d -r1.31.2.7 -r1.31.2.8
> >> --- batcast.mx 18 Feb 2010 01:04:05 -0000 1.31.2.7
> >> +++ batcast.mx 20 Mar 2010 12:53:10 -0000 1.31.2.8
> >> @@ -248,6 +248,8 @@
> >> BAT *b,*bn;
> >> BATiter bi;
> >> BUN p, q, r = 0;
> >> + ptr v = NULL;
> >> + int len = 0;
> >>
> >> @:getBATdescriptor(bid, b, "batca...@1")@
> >> @:voidresultBAT(ty...@1,"batca...@1")@
> >> @@ -255,15 +257,12 @@
> >>
> >> BATaccessBegin(b, USE_TAIL, MMAP_SEQUENTIAL);
> >> BATloop(b, p, q) {
> >> - ptr v = NULL;
> >> - int len = 0;
> >> -
> >> ATOMfromstr(ty...@1, &v, &len, (char *) BUNtvar(bi, p));
> >> ATOMput(ty...@1, bn->T->vheap, Tloc(bn, r), v);
> >> - if (ATOMextern(ty...@1))
> >> - GDKfree(v);
> >> r++;
> >> }
> >> + if (ATOMextern(ty...@1))
> >> + GDKfree(v);
> >> BATsetcount(bn, BATcount(b));
> >> bunins_failed:
> >> BATaccessEnd(b, USE_TAIL, MMAP_SEQUENTIAL);
> >>
> >>
> >> ------------------------------------------------------------------------------
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> >>
> >
>
>
> ------------------------------------------------------------------------------
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--
| Dr. Stefan Manegold | mailto:stefan.maneg...@cwi.nl |
| CWI, P.O.Box 94079 | http://www.cwi.nl/~manegold/ |
| 1090 GB Amsterdam | Tel.: +31 (20) 592-4212 |
| The Netherlands | Fax : +31 (20) 592-4199 |
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