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From: Lars Schneider <larsxschneider@gmail.com>
To: Eric Wong <e@80x24.org>
Cc: git@vger.kernel.org
Subject: Re: RFC: Enable delayed responses to Git clean/smudge filter requests
Date: Tue, 15 Nov 2016 15:29:09 +0100
Message-ID: <5BC69AC1-5499-4F73-816A-D8786106D796@gmail.com> (raw)
In-Reply-To: <20161115010356.GA29602@starla>


> On 15 Nov 2016, at 02:03, Eric Wong <e@80x24.org> wrote:
> 
> Lars Schneider <larsxschneider@gmail.com> wrote:
>> Hi,
>> 
>> Git always performs a clean/smudge filter on files in sequential order.
>> Sometimes a filter operation can take a noticeable amount of time. 
>> This blocks the entire Git process.
> 
> I have the same problem in many places which aren't git :>
> 
>> I would like to give a filter process the possibility to answer Git with
>> "I got your request, I am processing it, ask me for the result later!".
>> 
>> I see the following way to realize this:
>> 
>> In unpack-trees.c:check_updates() [1] we loop through the cache 
>> entries and "ask me later" could be an acceptable return value of the 
>> checkout_entry() call. The loop could run until all entries returned
>> success or error.
>> 
>> The filter machinery is triggered in various other places in Git and
>> all places that want to support "ask me later" would need to be patched 
>> accordingly.
> 
> That all sounds reasonable.
> 
> The filter itself would need to be aware of parallelism
> if it lives for multiple objects, right?

Correct. This way Git doesn't need to deal with threading...


>> Do you think this could be a viable approach?
> 
> It'd probably require a bit of work, but yes, I think it's viable.
> 
> We already do this with curl_multi requests for parallel
> fetching from dumb HTTP servers, but that's driven by curl
> internals operating with a select/poll loop.
> 
> Perhaps the curl API could be a good example for doing this.

Thanks for the pointer!


>> Do you see a better way?
> 
> Nope, I prefer non-blocking state machines to threads for
> debuggability and determinism.

Agreed!


> Anyways, I'll plan on doing something similar (in Perl) with the
> synchronous parts of public-inbox which relies on "cat-file --batch"
> at some point... (my rotational disks are sloooooooow :<)

That sounds interesting! What changes to you have in mind for 
"cat-file --batch"? We are thinking about performance improvements
in that area, too. I would be happy to help reviewing your patches!

Thanks a lot for your RFC feedback,
Lars

  reply	other threads:[~2016-11-15 14:29 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-14 21:09 Lars Schneider
2016-11-15  1:03 ` Eric Wong
2016-11-15 14:29   ` Lars Schneider [this message]
2016-11-15 18:03     ` Junio C Hamano
2016-11-16  9:53       ` Lars Schneider
2016-11-16 18:15         ` Junio C Hamano
2016-11-16 18:47           ` Lars Schneider
2016-11-16 19:19             ` Junio C Hamano
2016-11-16 22:41         ` Jakub Narębski
2016-11-16 23:46           ` Junio C Hamano
2016-11-17  9:19             ` Lars Schneider
2016-11-24 15:45       ` Lars Schneider
2016-11-28 21:48         ` Junio C Hamano
2016-11-15 18:27     ` Eric Wong
2017-01-09 20:44 ` Stefan Beller
2017-01-11 12:57   ` Lars Schneider

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