Re: [PATCH 7/9] fetch: fetch submodules in parallel

[Stefan Beller <sbeller@google.com>]

On Fri, Aug 28, 2015 at 11:27 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Jonathan Nieder <jrnieder@gmail.com> writes:
>
>> Junio C Hamano wrote:
>>
>>> My preference is still (1) leave standard error output all connected
>>> to the same fd without multiplexing, and (2) line buffer standard
>>> output so that the output is at least readable as a text, in a
>>> similar way a log of an irc channel where everybody is talking at
>>> the same time.
>>
>> There is something nice about the immediacy of seeing output from all
>> the subprocesses at the same time in that model.
>>
>> But for commands that show progress like "git clone", "git checkout",
>> and "git fetch", it does not work well at all.  They provide output
>> that updates itself by putting a carriage return at the end of each
>> chunk of output, like this:
>>
>>  remote: Finding sources:  11% (18/155)           \r
>>  remote: Finding sources:  12% (19/155)           \r
>>
>> With multiple commands producing such output, they will overwrite each
>> other's lines, producing a mixture that is confusing and unuseful.
>
> That example also illustrates why it is not a useful to buffer all
> of these lines and showing them once.
>
>> Ideally what I as a user want to see is something like what "prove"
>> writes, showing progress on the multiple tasks that are taking place
>> at once:
>>
>>  ===(     103;1  0/?  8/?  3/?  11/?  6/?  16/?  1/?  1/? )==============
>
> Tell me how that "buffer all and show them once" helps us to get
> near that ideal.

It doesn't, but it looks better than the irc like everybody speaks at
the same time
solution IMHO.

At the very the user may not even be interested in the details similar
to what prove
provides. The client can estimate its own total progress by weighting
the progress
from all tasks.

>
>> That would require more sophisticated inter-process communication than
>> seems necessary for the first version of parallel "git submodule
>> update".
>
> Exactly.  Why waste memory to buffer and stall the entire output
> from other processes in the interim solution, then?
>
>