From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org
Subject: Re: [PATCH] xrealloc: do not reuse pointer freed by zero-length realloc()
Date: Tue, 1 Sep 2020 10:24:18 -0400 [thread overview]
Message-ID: <a176961b-645f-4dcb-3439-596f814891f4@gmail.com> (raw)
In-Reply-To: <20200901135105.GA3284077@coredump.intra.peff.net>
On 9/1/2020 9:51 AM, Jeff King wrote:
> On Tue, Sep 01, 2020 at 09:04:36AM -0400, Derrick Stolee wrote:
>> Adding an `if (!size) {free(ptr); return NULL;}` block was what I
>> expected. Was that chosen just so we can rely more on the system
>> realloc(), or is there a performance implication that I'm not
>> seeing?
>
> I went back and forth on whether to do that or not. This case should
> basically never happen, so I like both the performance and readability
> of only triggering it when realloc() returns NULL. But it would get rid
> of the hand-waving above, and I doubt the performance is measurable.
>
> If we do handle it up-front, then I think we'd actually want:
>
> if (!size) {
> free(ptr);
> return xmalloc(0);
> }
>
> (i.e., to never return NULL for consistency with xmalloc() and
> xcalloc()).
Good point. In that sense, your change makes a lot more
sense for staying consistent without strangeness like xmalloc(0).
>>> @@ -120,7 +120,7 @@ void *xrealloc(void *ptr, size_t size)
>>> memory_limit_check(size, 0);
>>> ret = realloc(ptr, size);
>>> if (!ret && !size)
>>> - ret = realloc(ptr, 1);
>>> + ret = realloc(ret, 1);
>>
>> I appreciate all the additional context for such a small change.
>
> Somebody's got to complete with you for ratio of commit message to diff
> lines. :)
Pretty sure I have a long way to match, but it is important to
have goals.
-Stolee
next prev parent reply other threads:[~2020-09-01 14:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 11:18 [PATCH] xrealloc: do not reuse pointer freed by zero-length realloc() Jeff King
2020-09-01 13:04 ` Derrick Stolee
2020-09-01 13:51 ` Jeff King
2020-09-01 14:24 ` Derrick Stolee [this message]
2020-09-01 15:58 ` Junio C Hamano
2020-09-02 7:54 ` Jeff King
2020-09-02 19:19 ` Junio C Hamano
2020-09-03 3:50 ` Jonathan Nieder
2020-09-01 15:20 ` Andreas Schwab
2020-09-01 15:56 ` Junio C Hamano
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