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Re: allowing multiple PQclear() calls

From: Boszormenyi Zoltan <zb(at)cybertec(dot)at>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
Cc: Marko Kreen <markokr(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Kupershmidt <schmiddy(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: allowing multiple PQclear() calls
Date: 2013-01-02 16:02:46
Message-ID: 50E45A26.8030307@cybertec.at (view raw or flat)
Thread:
Lists: pgsql-hackers
2013-01-02 16:52 keltezéssel, Heikki Linnakangas írta:
> On 02.01.2013 17:27, Marko Kreen wrote:
>> On Wed, Jan 2, 2013 at 5:11 PM, Boszormenyi Zoltan<zb(at)cybertec(dot)at>  wrote:
>>> 2012-12-11 16:09 keltezéssel, Simon Riggs írta:
>>>
>>>> On 11 December 2012 12:18, Boszormenyi Zoltan<zb(at)cybertec(dot)at>  wrote:
>>>>
>>>>>>> Such mechanism already exist - you just need to set
>>>>>>> your PGresult pointer to NULL after each PQclear().
>>>>>>
>>>>>> So why doesn't PQclear() do that?
>>>>>
>>>>>
>>>>> Because then PQclear() would need a ** not a *. Do you want its
>>>>> interface changed for 9.3 and break compatibility with previous versions?
>>>>
>>>> No, but we should introduce a new public API call that is safer,
>>>> otherwise we get people continually re-inventing new private APIs that
>>>> Do the Right Thing, as the two other respondents have shown.
>>>>
>>>
>>> How about these macros?
>>
>> * Use do { } while (0) around the macros to get proper statement behaviour.
>> * The if() is not needed, both PQclear and PQfinish do it internally.
>> * Docs
>>
>> Should the names show somehow that they are macros?
>> Or is it enough that it's mentioned in documentation?
>
> IMHO this doesn't belong into libpq, the interface is fine as it is. It's the caller's 
> responsibility to set the pointer to NULL after PQclear(), same as it's the caller's 
> responsibility to set a pointer to NULL after calling free(), or to set the fd variable 
> to -1 after calling close(fd). There's plenty of precedence for this pattern, and it 
> shouldn't surprise any programmer.

Let me quote Simon Riggs here:
> ... we should introduce a new public API call that is safer,
> otherwise we get people continually re-inventing new private APIs that
> Do the Right Thing, as the two other respondents have shown.

Best regards,
Zoltán Böszörményi

-- 
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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de
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