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

Jonathan Nieder [off-list ref] writes:

Junio C Hamano wrote:

quoted

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.

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?