Re: [PATCH v3 2/2] transport-helper: check if remote helper is alive

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Apr 8, 2013, 19:08 UTC
Message-ID: <CAMP44s0DjJL44uavM44sxgSyrgbTLpUarEPB6=-imvw1rewOOA@mail.gmail.com>
In-Reply-To: <7vwqscx3l5.fsf@alter.siamese.dyndns.org>

On Mon, Apr 8, 2013 at 1:46 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 11 quoted lines

>>> ...  But if we keep
>>> helper running, who will be communicating with it via these open
>>> pipes?  The process that is calling finish_command() on fast-import
>>> and disconnecting from the helper won't be, as read/write to the
>>> pipe, even if we do not disconnect from here, will result in errors
>>> if the helper has already exited at this point.
>>
>> Nobody will send any further input, but in theory we could redirect
>> the pipe and send more commands. That's how it was designed.
>
> Who does the redirection to whom?

The one that is doing all the redirections, transport-helper.

> How would the process tree and
> piping constructed around the current system?

I cannot parse that correctly, but transport-helper is already receiving the output from the remote-helper.

Show 6 quoted lines

> I am not trying to say it is just theoretical mental exercise (which
> I have seen you do not do at all on this list). I am trying to find
> out what the practical use case is that you have in mind, because
> disconnecting will prove to be not an improvement but a regression
> for that use case.  But you do not have to answer this question
> directly, because...

As the gitifyhg developers effusively pointed out, it's useful to see which mercurial revision corresponds to certain git revision, and this is best achieved through notes. Implementing this in the remote-helper doesn't make much sense (I won't go into details).

>> And in fact, I'm thinking doing exactly that, so we can send another
>> command to fetch the foreign commit ids and append notes with them.
>
> ...we will see the answer in that change anyway.

That doesn't change the fact that transport-helper would end up with mixed and matched design. Maybe the use-case above wouldn't be prevented by this change, but I think further changes would need to be done to the file to not end up in this weird state.

Cheers.

-- Felipe Contreras