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

[Lars Schneider <larsxschneider@gmail.com>]

> On 29 Sep 2016, at 18:57, Junio C Hamano <gitster@pobox.com> wrote:
> 
> Torsten Bögershausen <tboegi@web.de> writes:
> 
>>> 1) Git exits
>>> 2) The filter process receives EOF and prints "STOP" to the log
>>> 3) t0021 checks the content of the log
>>> 
>>> Sometimes 3 happened before 2 which makes the test fail.
>>> (Example: https://travis-ci.org/git/git/jobs/162660563 )
>>> 
>>> I added a this to wait until the filter process terminates:
>>> 
>>> +wait_for_filter_termination () {
>>> +	while ps | grep -v grep | grep -F "/t0021/rot13-filter.pl" >/dev/null 2>&1
>>> +	do
>>> +		echo "Waiting for /t0021/rot13-filter.pl to finish..."
>>> +		sleep 1
>>> +	done
>>> +}
>>> 
>>> Does this look OK to you?
>> Do we need the ps at all ?
>> How about this:
>> 
>> +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 have a feeling that the machinery being tested needs to be fixed
> so that the sequence is always be:
> 
>    0) Git spawns the filter process, as it needs some contents to
>       be filtered.
> 
>    1) Git did everything it needed to do and decides that is time
>       to go.
> 
>    2) Filter process receives EOF and prints "STOP" to the log.
> 
>    3) Git waits until the filter process finishes.
> 
>    4) t0021, after Git finishes, checks the log.
> 
> Repeated sleep combined with grep is probably just sweeping the real
> problem under the rug.  Do we have enough information to do the
> above?
> 
> An inspiration may be in the way we centrally clean all tempfiles
> and lockfiles before exiting.  We have a central registry of these
> files that need cleaning up and have a single atexit(3) handler to
> clean them up.  Perhaps we need a registry that filter processes
> spawned by the mechanism Lars introduces in this series, and have an
> atexit(3) handler that closes the pipe to them (which signals the
> filters that it is time for them to go) and wait(2) on them, or
> something?  I do not think we want any kill(2) to be involved in
> this clean-up procedure, but I do think we should wait(2) on what we
> spawn, as long as these processes are meant to be shut down when the
> main process of Git exits (this is different from things like
> credential-cache daemon where they are expected to persist and meant
> to serve multiple Git processes).

We discussed that issue in v4 and v6:
http://public-inbox.org/git/20160803225313.pk3tfe5ovz4y3i7l@sigill.intra.peff.net/
http://public-inbox.org/git/xmqqbn0a3wy3.fsf@gitster.mtv.corp.google.com/

My impression was that you don't want Git to wait for the filter process.
If Git waits for the filter process - how long should Git wait?

Thanks,
Lars