Re: [PATCH] builtin/commit.c: memoize git-path for COMMIT_EDITMSG

[Pranit Bauva <pranit.bauva@gmail.com>]

Hey Matthieu,

On Tue, May 24, 2016 at 1:41 PM, Matthieu Moy
<Matthieu.Moy@grenoble-inp.fr> wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
>> Pranit Bauva <pranit.bauva@gmail.com> writes:
>>
>>>  static const char *use_message_buffer;
>>> -static const char commit_editmsg[] = "COMMIT_EDITMSG";
>>> +static const char commit_editmsg_path[] = git_path_commit_editmsg();
>>
>> The function defined with the macro looks like
>>
>>       const char *git_path_commit_editmsg(void)
>>         {
>>               static char *ret;
>>                 if (!ret)
>>                       ret = git_pathdup("COMMIT_EDITMSG");
>>               return ret;
>>       }
>>
>> so receiving its result to "const char v[]" looks somewhat
>> suspicious.
>>
>> More importantly, when is this function evaluated and returned value
>> used to fill commit_editmsg_path[]?
>
> I may have missed something, but I'd say "never", as the code is not
> compilable at least with my gcc:
>
> builtin/commit.c:98:1: error: invalid initializer
>  static const char commit_editmsg_path[] = git_path_commit_editmsg();
>  ^
>
> AFAIK, initializing a global variable with a function call is allowed in
> C++, but not in C.

I wasn't aware of this fact. Thanks.

> And indeed, this construct is a huge source of trouble, as it would mean
> that git_path_commit_editmsg() is called 1) unconditionnally, and 2)
> before entering main().
>
> 1) means that the function call is made even when git is called for
> another command. This is terrible for the startup time: if all git
> commands have a not-totally-immediate initializer, then all commands
> would need to run the initializers for all other commands. 2) means it's
> a nightmare to debug, as you can hardly predict when the code will be
> executed.

Yes I agree that this approach will definitely cause a lot of
problems. I will re-roll with how Junio suggested.

> --
> Matthieu Moy
> http://www-verimag.imag.fr/~moy/
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