Re: [HACKERS] Problem returning strings with pgsql 8.3.x

On Tue, May 13, 2008 at 8:01 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Martijn van Oosterhout <kleptog@svana.org> writes:
> > On Mon, May 12, 2008 at 11:23:17PM -0600, Josh Tolley wrote:
> >> SPI_push();
> >> retval =
> >> InputFunctionCall(&flinfo, lolVarGetString(returnVal, true),
> >> resultTypeIOParam, -1);
> >> SPI_pop();
>
> > Won't this cause the return value to be allocated inside a new memory
> > block which gets freeds at the SPI_pop?
>
> The SPI_pop in itself is harmless ... the problem is the SPI_finish
> further down, which will release all simple palloc's done within the
> SPI function context. What he needs is something comparable to this bit
> in plpgsql:
>
> /*
> * If the function's return type isn't by value, copy the value
> * into upper executor memory context.
> */
> if (!fcinfo->isnull && !func->fn_retbyval)
> {
> Size len;
> void *tmp;
>
> len = datumGetSize(estate.retval, false, func->fn_rettyplen);
> tmp = SPI_palloc(len);
> memcpy(tmp, DatumGetPointer(estate.retval), len);
> estate.retval = PointerGetDatum(tmp);
> }
>
> ie, push the data into something allocated with SPI_palloc().

I'll give this a shot as soon as I can... many thanks

> I would bet large amounts of money that the problem is not "new in
> 8.3.0", either. Perhaps Josh was not testing in an --enable-cassert
> (CLOBBER_FREED_MEMORY) build before.

I'll check... that's definitely not unlikely. Again, thanks.

- Josh

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