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

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Aug 28, 2015, 18:20 UTC
Message-ID: <20150828182008.GC8165@google.com>
In-Reply-To: <xmqqfv332v84.fsf@gitster.mtv.corp.google.com>

Junio C Hamano wrote:

Show 5 quoted lines

> 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.

Even with --no-progress, there is a similar sense of confusion in the intermixed output. Error messages are hard to find. This is a comment complaint about the current "repo sync -j" implementation.

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/? )==============

That would require more sophisticated inter-process communication than seems necessary for the first version of parallel "git submodule update". For the first version that people use in the wild, showing output from one of the tasks at a time, simulating a sped-up sequential implementation, seems useful to me.

In the degenerate case where only one task is running, it reduces to the current output. The output is familiar and easy to use. I quite like the approach.

My two cents, Jonathan