Re: [PATCH v1] convert: add "status=delayed" to filter process protocol

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 8, 2017, 23:42 UTC
Message-ID: <xmqqa8b115ll.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170108191736.47359-1-larsxschneider@gmail.com>

larsxschneider@gmail.com writes:

Show 11 quoted lines

> From: Lars Schneider <larsxschneider@gmail.com>
>
> Some `clean` / `smudge` filters might require a significant amount of
> time to process a single blob. During this process the Git checkout
> operation is blocked and Git needs to wait until the filter is done to
> continue with the checkout.
>
> Teach the filter process protocol (introduced in edcc858) to accept the
> status "delayed" as response to a filter request. Upon this response Git
> continues with the checkout operation and asks the filter to process the
> blob again after all other blobs have been processed.

Hmm, I would have expected that the basic flow would become

	for each paths to be processed:
		convert-to-worktree to buf
		if not delayed:
			do the caller's thing to use buf
		else:
			remember path

	for each delayed paths:
		ensure filter process finished processing for path
		fetch the thing to buf from the process
		do the caller's thing to use buf

and that would make quite a lot of sense. However, what is actually implemented is a bit disappointing from that point of view. While its first part is the same as above, the latter part instead does:

	for each delayed paths:
		checkout the path

Presumably, checkout_entry() does the "ensure that the process is done converting" (otherwise the result is simply buggy), but what disappoints me is that this does not allow callers that call "convert-to-working-tree", whose interface is obtain the bytestream in-core in the working tree representation, given an object in the object-db representation in an in-core buffer, to _use_ the result of the conversion. The caller does not have a chance to even see the result as it is written straight to the filesystem, once it calls checkout_delayed_entries().