Re: [Python-Dev] Py_SETREF vs. Py_XSETREF

[Guido van Rossum]

Agreed, let's go with two macros. The time discussing this further
could be spent more productively.

On Mon, Apr 4, 2016 at 2:35 AM, Victor Stinner  wrote:
> If some dev don't want to use the single macro for good or bad reasons, it's
> maybe better to have two macros to generalize their usage. The macro makes
> to C code shorter and easier to review.
>
> Victor
>
>
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Re: [Python-Dev] Py_SETREF vs. Py_XSETREF

[Victor Stinner]

If some dev don't want to use the single macro for good or bad reasons,
it's maybe better to have two macros to generalize their usage. The macro
makes to C code shorter and easier to review.

Victor
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Re: [Python-Dev] Py_SETREF vs. Py_XSETREF

[Nick Coghlan]

On 3 April 2016 at 17:32, Serhiy Storchaka  wrote:
> Originally I proposed a pair of macros for safe reference replacing to
> reflects the duality of Py_DECREF/Py_XDECREF. [1], [2]  The one should use
> Py_DECREF and the other should use Py_XDECREF.
>
> But then I got a number of voices for the single name [3], and no one voice
> (except mine) for the pair of names. Thus in final patches the single name
> Py_SETREF that uses Py_XDECREF is used. Due to adding some overhead in
> comparison with using Py_DECREF, this macros is not used in critical
> performance code such as PyDict_SetItem().

I was one of those arguing for the single macro, and I think Alexander
raises a good point in http://bugs.python.org/issue26200#msg262204
that I don't recall seeing in the original discussion: the "X" in the
macro serves as a good shorthand for indicating that the code in
question isn't closely tracking whether or not manipulated reference
might be NULL, and hence may be a good candidate for additional
micro-optimisations that keep better track of whether or not the
pointer is NULL.

> Should we rename Py_SETREF to Py_XSETREF and introduce new Py_SETREF that
> uses Py_DECREF?

With the single-macro design put into effect and concrete problems
arising from that, I'm now more persuaded by the consistency argument
than I was originally, so +1 from me for reverting to your original
dual-macro proposal.

Cheers,
Nick.

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Nick Coghlan   |   ncogh...@gmail.com   |   Brisbane, Australia
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Re: [Python-Dev] Py_SETREF vs. Py_XSETREF

[Armin Rigo]

Hi,

On 3 April 2016 at 15:29, MRAB  wrote:
>> Should we rename Py_SETREF to Py_XSETREF and introduce new Py_SETREF
>> that uses Py_DECREF?
>
> Checking for NULL is convenient (and safer), but, on the other hand, it
> _would_ be consistent with the others.

My 2 cents would be to call the new macro Py_XSETREF for consistency,
at least, whether you decide to go with two macros or not.  Otherwise
it's kind of obvious that if you add Py_SETREF that checks for nulls,
in 2 or 3 releases people will really want a "fast" variant anyway,
and there will be no consistent name for that.


A bientôt,

Armin.
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Re: [Python-Dev] Py_SETREF vs. Py_XSETREF

[MRAB]

On 2016-04-03 08:32, Serhiy Storchaka wrote:

Originally I proposed a pair of macros for safe reference replacing to
reflects the duality of Py_DECREF/Py_XDECREF. [1], [2]  The one should
use Py_DECREF and the other should use Py_XDECREF.

But then I got a number of voices for the single name [3], and no one
voice (except mine) for the pair of names. Thus in final patches the
single name Py_SETREF that uses Py_XDECREF is used. Due to adding some
overhead in comparison with using Py_DECREF, this macros is not used in
critical performance code such as PyDict_SetItem().

Now Raymond says that we should have separate Py_SETREF/Py_XSETREF names
to avoid any overhead. [4]  And so I'm raising this issue on Python-Dev.

Should we rename Py_SETREF to Py_XSETREF and introduce new Py_SETREF
that uses Py_DECREF?

[1] http://comments.gmane.org/gmane.comp.python.devel/145346
[2] http://comments.gmane.org/gmane.comp.python.devel/145974
[3] http://bugs.python.org/issue26200#msg259784
[4] http://bugs.python.org/issue26200

Checking for NULL is convenient (and safer), but, on the other hand, it 
_would_ be consistent with the others.

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