Re: [PATCH v8 00/11] Git filter protocol

[Jeff King <peff@peff.net>]

On Thu, Sep 29, 2016 at 09:57:57AM -0700, Junio C Hamano wrote:

> > +wait_for_filter_termination () {
> > +	while ! grep "STOP"  LOGFILENAME >/dev/null
> > +	do
> > +		echo "Waiting for /t0021/rot13-filter.pl to finish..."
> > +		sleep 1
> > +	done
> > +}
> 
> Running "ps" and grepping for a command is not suitable for script
> to reliably tell things, so it is out of question.  Compared to
> that, your version looks slightly better, but what if the machinery
> that being tested, i.e. the part that drives the filter process, is
> buggy or becomes buggy and causes the filter process that writes
> "STOP" to die before it actually writes that string?

I'm of the opinion that any busy-waiting is a good sign that something
is suboptimal. The right solution here seems like it should be signaling
the test script via a descriptor.

I don't necessarily agree, though, that the timing of filter-process
cleanup needs to be part of the public interface. So in your list:

>     3) Git waits until the filter process finishes.

That seems simple and elegant, but I can think of reasons we might not
want to wait (e.g., if the filter has to do some maintenance task and
does not the user to have to wait).

OTOH, we already face this in git, and we solve it by explicitly
backgrounding the maintenance task (i.e., auto-gc). So one could argue
that it is the responsibility of the filter process to manage its own
processes. It certainly makes the interaction with git simpler.

-Peff