Junio C Hamano <gitster@xxxxxxxxx> writes:
> "John Cai via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes:
>
>> From: John Cai <johncai86@xxxxxxxxx>
>>
>> When format is passed into --batch, --batch-check, --batch-command,
>> the format gets expanded. When nothing is passed in, the default format
>> is set and the expand_format() gets called.
>>
>> We can save on these cycles by hardcoding how to print the
>> information when nothing is passed as the format, or when the default
>> format is passed. There is no need for the fully expanded format with
>> the default. Since batch_object_write() happens on every object provided
>> in batch mode, we get a nice performance improvement.
>
> That is OK in principle, but ...
>
>> + if (!opt->format && !opt->print_contents) {
>> + char buf[1024];
>> +
>> + print_default_format(buf, 1024, data);
>> + batch_write(opt, buf, strlen(buf));
>> + goto cleanup;
>> + }
>> +
>> + fmt = opt->format ? opt->format : default_format;
>
> ... instead of doing this, wouldn't it be nicer to base the decision
> to call print_default_format() on purely the contents of the format,
> i.e.
>
> fmt = opt->format ? opt->format : default_format;
> if (!strcmp(fmt, DEFAULT_FORMAT) && !opt->print_contents) {
> ... the above print_default_format() call block here ...
> goto cleanup;
> }
>
> where DEFAULT_FORMAT is
>
> #define DEFAULT_FORMAT = "%(objectname) %(objecttype) %(objectsize)"
>
> and
>
>> @@ -515,9 +543,7 @@ static int batch_objects(struct batch_options *opt)
>> struct expand_data data;
>> int save_warning;
>> int retval = 0;
>> -
>> - if (!opt->format)
>> - opt->format = "%(objectname) %(objecttype) %(objectsize)";
>
> retain the defaulting with
>
> if (!opt->format)
> opt->format = DEFAULT_FORMAT;
>
> instead of making opt->format == NULL to mean something special?
>
> That way, even if the user-input happens to name the format that is
> identical to DEFAULT_FORMAT, because we only care what the format
> is, and not where the format comes from, we will get the same
> optimization. Wouldn't it make more sense?
Actually, doing that literally and naively would not be a good idea,
as the special case code is inside batch_object_write() that is
called once per each object, and because the format used will not
change for each call, doing strcmp() every time is wasteful. The
same is true for
fmt = opt->format ? opt->format : default_format;
as opt->format will not change across calls to this function.
So, if we were to do this optimization:
* we key on the fact that opt->format is NULL to trigger the
optimization inside batch_object_write(), so that we do not have
to strcmp(DEFAULT_FORMAT, fmt) for each and every object.
* a while loop in batch_objects() or for_each_*_object() calls is
what calls batch_object_write() for each object. So somewhere
early in that function (or before we enter the function), we can
check opt->format and
- if it is NULL, we can leave it NULL.
- if it is the same as DEFAULT_FORMAT, clear it to NULL.
so that the optimization in batch_object_write() can cheaply kick
in.
would be a good way to go, perhaps?
