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From: "René Scharfe" <l.s.r@web.de>
To: Jeff King <peff@peff.net>
Cc: "Git List" <git@vger.kernel.org>,
	"Martin Ågren" <martin.agren@gmail.com>,
	"Christian Couder" <christian.couder@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>
Subject: Re: [PATCH] revision: introduce prepare_revision_walk_extended()
Date: Mon, 18 Dec 2017 20:18:19 +0100	[thread overview]
Message-ID: <39581cd0-0bfd-c8d1-642b-1245cf425ab4@web.de> (raw)
In-Reply-To: <20171218151043.GA9449@sigill.intra.peff.net>

Am 18.12.2017 um 16:10 schrieb Jeff King:
> On Sat, Dec 16, 2017 at 01:12:16PM +0100, René Scharfe wrote:
> 
>> prepare_revision_walk() allows callers to take ownership of the array of
>> pending objects by setting the rev_info flag "leak_pending" and copying
>> the object_array "pending".  They use it to clear commit marks after
>> setup is done.  This interface is brittle enough that it requires
>> extensive comments.
>>
>> Provide an easier way by adding a function that can hand over the array
>> to a caller-supplied output parameter and converting all users of the
>> flag "leak_pending" to call prepare_revision_walk_extended() instead.
> 
> I think this is _better_, but it's still kind of a funny interface.
> 
> The root of the matter is that the revision-walking code doesn't clean
> up after itself. In every case, the caller is just saving these to clean
> up commit marks, isn't it?

bundle also checks if the pending objects exists.

> Could we instead have an interface like:
> 
>    revs.clear_commit_marks = 1;
>    prepare_revision_walk(&revs);
>    ...
>    finish_revision_walk(&revs);
> 
> where that final function would do any cleanup, including clearing the
> commit marks. I suspect there are other small bits that get leaked
> because there's not really any "destructor" for a revision walk.
> 
> It's not as flexible as this whole "make a copy of the pending tips"
> thing, but it keeps all of the details abstracted away from the callers.
> 
> Alternatively:
> 
>> +`prepare_revision_walk_extended`::
>> +
>> +	Like prepare_revision_walk(), but allows callers to take ownership
>> +	of the array of pending objects by passing an object_array pointer
>> +	as the second parameter; passing NULL clears the array.
> 
> What if we just got rid of this function and had callers do:
> 
>    object_array_copy(&old_pending, &revs);
>    prepare_revision_walk(&revs);
>    ...
>    clear_commit_marks_for_object_array(&old_pending);
> 
> That sidesteps all of the memory ownership issues by just creating a
> copy. That's less efficient, but I'd be surprised if it matters in
> practice (we tend to do one or two revisions per process, there don't
> tend to be a lot of pending tips, and we're really just talking about
> copying some pointers here).

This was done before I added the leak_pending flag.

t5502 and t5571 have test cases with ca. 1000 pending objects, t5551
and t5541 with ca. 2000, p5310 more than 8000.  That's just a few KB.

I don't know if there can be real-world use cases with millions of
entries (when it would start to hurt).

Why does prepare_revision_walk() clear the list of pending objects at
all?  Assuming the list is append-only then perhaps remembering the
last handled index would suffice.

René

  reply	other threads:[~2017-12-18 19:18 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-16 12:12 René Scharfe
2017-12-17 10:20 ` Martin Ågren
2017-12-18 15:10 ` Jeff King
2017-12-18 19:18   ` René Scharfe [this message]
2017-12-19 11:49     ` Jeff King
2017-12-19 18:33       ` Junio C Hamano
2017-12-20 13:08         ` Jeff King
2017-12-21 18:41           ` René Scharfe
2017-12-24 14:22             ` Jeff King
2017-12-25 17:36               ` René Scharfe
2017-12-25 17:41 ` [PATCH v2 0/9] revision: get rid of the flag leak_pending René Scharfe
2017-12-25 17:43   ` [PATCH v2 1/9] commit: avoid allocation in clear_commit_marks_many() René Scharfe
2018-01-10  7:54     ` Jeff King
2017-12-25 17:44   ` [PATCH v2 2/9] commit: use clear_commit_marks_many() in remove_redundant() René Scharfe
2017-12-25 17:44   ` [PATCH v2 3/9] ref-filter: use clear_commit_marks_many() in do_merge_filter() René Scharfe
2017-12-25 17:44   ` [PATCH v2 4/9] object: add clear_commit_marks_all() René Scharfe
2018-01-10  7:58     ` Jeff King
2018-01-11 18:57       ` René Scharfe
2018-01-12 15:20         ` Jeff King
2017-12-25 17:45   ` [PATCH v2 5/9] bisect: avoid using the rev_info flag leak_pending René Scharfe
2018-01-10  8:07     ` Jeff King
2018-01-11 18:57       ` René Scharfe
2018-01-12 15:23         ` Jeff King
2017-12-25 17:46   ` [PATCH v2 6/9] bundle: " René Scharfe
2017-12-28 21:13     ` Junio C Hamano
2018-01-10  8:18     ` Jeff King
2017-12-25 17:47   ` [PATCH v2 7/9] checkout: " René Scharfe
2017-12-28 21:24     ` Junio C Hamano
2017-12-25 17:47   ` [PATCH v2 8/9] revision: remove the unused " René Scharfe
2017-12-25 17:48   ` [PATCH v2 9/9] commit: remove unused function clear_commit_marks_for_object_array() René Scharfe
2017-12-28 20:32   ` [PATCH v2 0/9] revision: get rid of the flag leak_pending Junio C Hamano
2018-01-10  8:20   ` Jeff King

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