Thread: Re: PG_GETARG_GISTENTRY?

Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Mar 29, 2017 at 11:54 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Andres Freund <andres@anarazel.de> writes:
>>> we have a good number of '(GISTENTRY *) PG_GETARG_POINTER(n)' in our
>>> code - looks a bit better & shorter to have PG_GETARG_GISTENTRY(n).

>> Should be PG_GETARG_GISTENTRY_P to match existing conventions,
>> otherwise +1

> I have never quite understood why some of those macros have _P or _PP
> on the end and others don't.

_P means "pointer to".  _PP was introduced later to mean "pointer to
packed (ie, possibly short-header) datum".  Macros that mean to fetch
pointers to pass-by-ref data, but aren't using either of those naming
conventions, are violating project conventions, not least because you
don't know what they're supposed to do with short-header varlena input.
If I had a bit more spare time I'd run around and change any such macros.

In short, if you are supposed to write
FOO  *val = PG_GETARG_FOO(n);

then the macro designer blew it, because the name implies that it
returns FOO, not pointer to FOO.  This should be
FOO  *val = PG_GETARG_FOO_P(n);
        regards, tom lane

> On Apr 5, 2017, at 9:23 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Wed, Mar 29, 2017 at 11:54 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Andres Freund <andres@anarazel.de> writes:
>>>> we have a good number of '(GISTENTRY *) PG_GETARG_POINTER(n)' in our
>>>> code - looks a bit better & shorter to have PG_GETARG_GISTENTRY(n).
>
>>> Should be PG_GETARG_GISTENTRY_P to match existing conventions,
>>> otherwise +1
>
>> I have never quite understood why some of those macros have _P or _PP
>> on the end and others don't.
>
> _P means "pointer to".  _PP was introduced later to mean "pointer to
> packed (ie, possibly short-header) datum".  Macros that mean to fetch
> pointers to pass-by-ref data, but aren't using either of those naming
> conventions, are violating project conventions, not least because you
> don't know what they're supposed to do with short-header varlena input.
> If I had a bit more spare time I'd run around and change any such macros.
>
> In short, if you are supposed to write
>
>     FOO  *val = PG_GETARG_FOO(n);
>
> then the macro designer blew it, because the name implies that it
> returns FOO, not pointer to FOO.  This should be
>
>     FOO  *val = PG_GETARG_FOO_P(n);
>
>             regards, tom lane

I have written a patch to fix these macro definitions across src/ and contrib/.
Find the patch, attached.  All regression tests pass on my Mac laptop.

I don't find any inappropriate uses of _P where _PP would be called for.  I do,
however, notice that some datatypes' functions are written to use PG_GETARG_*_P
where PG_GETARG_*_PP might be more efficient.  Varbit's bitoctetlength function
could detoast only the header ala PG_DETOAST_DATUM_SLICE to return the
octet length, rather than detoasting the whole thing.  But that seems a different
issue, and patches to change that might have been rejected in the past so far as I
know, so I did not attempt any such changes here.

Mark Dilger

Mark Dilger <hornschnorter@gmail.com> writes:
> I have written a patch to fix these macro definitions across src/ and contrib/.
> Find the patch, attached.  All regression tests pass on my Mac laptop.

Thanks for doing the legwork on that.  This seems a bit late for v10,
especially since it's only cosmetic, but please put it in the first
v11 commitfest.

> I don't find any inappropriate uses of _P where _PP would be called for.  I do,
> however, notice that some datatypes' functions are written to use PG_GETARG_*_P
> where PG_GETARG_*_PP might be more efficient.

Yeah.  I think Noah did some work in that direction already, but I don't
believe he claimed to have caught everything.  Feel free to push further.
        regards, tom lane

> On Apr 5, 2017, at 1:12 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Mark Dilger <hornschnorter@gmail.com> writes:
>> I have written a patch to fix these macro definitions across src/ and contrib/.
>> Find the patch, attached.  All regression tests pass on my Mac laptop.
>
> Thanks for doing the legwork on that.

You are welcome.

> This seems a bit late for v10,
> especially since it's only cosmetic

Agreed.

> , but please put it in the first
> v11 commitfest.

Done.

>
>> I don't find any inappropriate uses of _P where _PP would be called for.  I do,
>> however, notice that some datatypes' functions are written to use PG_GETARG_*_P
>> where PG_GETARG_*_PP might be more efficient.
>
> Yeah.  I think Noah did some work in that direction already, but I don't
> believe he claimed to have caught everything.  Feel free to push further.

Thanks for clarifying.