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From:   Eric Sunshine <sunshine@sunshineco.com>
Date:   Tue, 15 Feb 2022 22:01:07 -0500
Message-ID: <CAPig+cQUwErXaZR-xZ8u9iz4kpEkE4G5QaxNRCuUx_Xt0rQ_-g@mail.gmail.com>
Subject: Re: [PATCH v7 4/4] cat-file: add --batch-command mode
To:     John Cai <johncai86@gmail.com>
Cc:     Junio C Hamano <gitster@pobox.com>,
        John Cai via GitGitGadget <gitgitgadget@gmail.com>,
        Git List <git@vger.kernel.org>, Taylor Blau <me@ttaylorr.com>,
        Phillip Wood <phillip.wood123@gmail.com>,
        =?UTF-8?B?w4Z2YXIgQXJuZmrDtnLDsCBCamFybWFzb24=?= <avarab@gmail.com>,
        Eric Wong <e@80x24.org>, Bagas Sanjaya <bagasdotme@gmail.com>,
        Jonathan Tan <jonathantanmy@google.com>,
        Christian Couder <christian.couder@gmail.com>
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On Tue, Feb 15, 2022 at 9:48 PM John Cai <johncai86@gmail.com> wrote:
> On 15 Feb 2022, at 20:28, Junio C Hamano wrote:
> > and make the caller do
> >
> >     dispatch_calls(opt, ..., nr);
> >     nr = 0;
> >
> > instead of passing a pointer to nr like the posted patch?
>
> Yeah, this is what I had before but there was discussion about separation of concerns in [1]. But perhaps it's preferable compared to passing a pointer to nr.
>
> 1. https://lore.kernel.org/git/CAPig+cTwLhn1GZ_=6s0FXL0z=Q=p1w9ZGK0hAV8wfK9RsQYjnA@mail.gmail.com/

My biggest concern when mentioning it during review was that if a
caller forgets to do `nr = 0`, then a sequence such as:

    dispatch_calls(...);
    ...
    dispatch_calls(...);

will send dangling pointers to the command handlers in the second
dispatch_calls() invocation because the first call to dispatch_calls()
did free(cmd[i].line). In that sense, it's an accident waiting to
happen if people modifying this code in the future aren't paying close
attention.

That said, I don't feel too strongly about it and mentioned in my
review that it might be "good enough" as-is (with the caller having to
remember to `nr = 0`) since it's a local helper function.