Re: [WIP/RFC 00/23] repository object

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Mon, May 29, 2017 at 12:36 PM, Duy Nguyen <pclouds@gmail.com> wrote:
> On Tue, May 23, 2017 at 2:35 AM, Jeff King <peff@peff.net> wrote:
>> On Thu, May 18, 2017 at 04:21:11PM -0700, Brandon Williams wrote:
>>
>>> When I first started working on the git project I found it very difficult to
>>> understand parts of the code base because of the inherently global nature of
>>> our code.  It also made working on submodules very difficult.  Since we can
>>> only open up a single repository per process, you need to launch a child
>>> process in order to process a submodule.  But you also need to be able to
>>> communicate other stateful information to the children processes so that the
>>> submodules know how best to format their output or match against a
>>> pathspec...it ends up feeling like layering on hack after hack.  What I would
>>> really like to do, is to have the ability to have a repository object so that I
>>> can open a submodule in-process.
>>
>> We could always buy in fully to the multi-process model and just
>> implement a generic RPC protocol between the parent and submodule gits.
>> Does CORBA still exist?
>>
>> (No, I am not serious about any of that).
>
> CORBA or not, submodule IPC is a real pain. That was what I felt
> reading the super-prefix changes a few weeks ago. Some operations
> might benefit from staying in the same process, but probably not all
> (and we lose process protection, which sometimes is a good thing)
>
>>> This is still very much in a WIP state, though it does pass all tests.  What
>>> I'm hoping for here is to get a discussion started about the feasibility of a
>>> change like this and hopefully to get the ball rolling.  Is this a direction we
>>> want to move in?  Is it worth the pain?
>>
>> I think the really painful part is going to be all of the system calls
>> that rely on global state provided by the OS. Like, say, every
>> filesystem call that expects to find working tree files without
>> prepending the working tree path.
>>
>> That said, even if we never reached the point where we could handle all
>> submodule requests in-process, I think sticking the repo-related global
>> state in a struct certainly could not hurt general readability. So it's
>> a good direction regardless of whether we take it all the way.
>
> I doubt we would reach the point where libgit.a can handle all
> submodule operations in-process either. That would put libgit.a in a
> direct competitor position with libgit2.

Wouldn't that be a good thing? We already have some users (e.g.
Microsoft) choosing not to use libgit and instead use git.git because
the latter is generally more mature, if git.git gains more libgit
features without harming other things it'll be more useful to more
people.