Re: RFC: Enable delayed responses to Git clean/smudge filter requests

> 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?

>> 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.