From: David Geier <geidav.pg@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Chao Li <li.evan.chao@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Consistently use palloc_object() and palloc_array()
Date: Fri, 28 Nov 2025 22:47:08 +0100
Message-ID: <1e7f0c17-a965-4d5b-ad88-b435a4d97490@gmail.com> (raw)
In-Reply-To: <524587.1764365323@sss.pgh.pa.us>
References: <ad0748d4-3080-436e-b0bc-ac8f86a3466a@gmail.com>
<ED821EDD-6A1B-45B8-9005-31BCFFCB5A48@gmail.com>
<a29b0cd9-576f-486f-ba45-5139ee33adcf@gmail.com>
<524587.1764365323@sss.pgh.pa.us>
On 28.11.2025 22:28, Tom Lane wrote:
> David Geier <geidav.pg@gmail.com> writes:
>> On 27.11.2025 00:03, Chao Li wrote:
>>> This is a large patch, I just take a quick look, and found that:
>>> - *phoned_word = palloc(sizeof(char) * strlen(word) + 1);
>>> + *phoned_word = palloc_array(char, strlen(word) + 1);
>>> And
>>> - params = (const char **) palloc(sizeof(char *));
>>> + params = palloc_object(const char *);
>>> Applying palloc_array and palloc_object to char type doesn’t seem to improve anything.
>
>> You mean because sizeof(char) is always 1 and hence we could instead
>> simply write:
>> *phoned_word = palloc(strlen(word) + 1);
>> params = palloc(1);
>> I think the _array and _object variants are more expressive and for sure
>> don't make the code less readable.
>
> Yeah, I agree these particular changes seem fine. When you're doing
> address arithmetic for a memcpy or such, it may be fine to wire in an
> assumption that sizeof(char) == 1, but I think doing that in other
> contexts is not particularly good style.
>
> Another thing to note is that the proposed patch effectively changes
> the expression evaluation order:
>
> - *phoned_word = palloc((sizeof(char) * strlen(word)) + 1);
> + *phoned_word = palloc(sizeof(char) * (strlen(word) + 1));
>
> Now, there's not actually any difference because sizeof(char) is 1,
> but if it hypothetically weren't, the new version is likely more
> correct. Presumably the +1 is meant to allow room for a trailing \0,
> which is a char.
Oh right. Good catch!
> It'd be a good idea to review the patch to see if there are any
> places where semantics are changed in a less benign fashion...
I intentionally tried to avoid any semantic changes but it's of course
possible something slipped through by accident.
It's some ~1700 occurrences in the patch. If it takes ~10 seconds to
check a single, it would take ~4.7h to review the entire patch.
If no one is willing to take this on, I could split up the patch in 4 to
5 that each can be reviewed by someone else.
--
David Geier
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To: pgsql-hackers@postgresql.org
Cc: geidav.pg@gmail.com, tgl@sss.pgh.pa.us, li.evan.chao@gmail.com
Subject: Re: Consistently use palloc_object() and palloc_array()
In-Reply-To: <1e7f0c17-a965-4d5b-ad88-b435a4d97490@gmail.com>
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