From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>,
Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, jonathantanmy@google.com,
Junio C Hamano <gitster@pobox.com>,
Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH 1/1] sha1-file: split OBJECT_INFO_FOR_PREFETCH
Date: Tue, 28 May 2019 20:29:36 -0400 [thread overview]
Message-ID: <f30f82f9-b07e-d6c3-5ccb-9b08b8424f7c@gmail.com> (raw)
In-Reply-To: <20190528205441.GB24650@sigill.intra.peff.net>
On 5/28/2019 4:54 PM, Jeff King wrote:
> On Tue, May 28, 2019 at 08:19:07AM -0700, Derrick Stolee via GitGitGadget wrote:
>
>> From: Derrick Stolee <dstolee@microsoft.com>
>>
>> The OBJECT_INFO_FOR_PREFETCH bitflag was added to sha1-file.c in 0f4a4fb1
>> (sha1-file: support OBJECT_INFO_FOR_PREFETCH, 2019-03-29) and is used to
>> prevent the fetch_objects() method when enabled.
>>
>> However, there is a problem with the current use. The definition of
>> OBJECT_INFO_FOR_PREFETCH is given by adding 32 to OBJECT_INFO_QUICK. This is
>> clearly stated above the definition (in a comment) that this is so
>> OBJECT_INFO_FOR_PREFETCH implies OBJECT_INFO_QUICK. The problem is that using
>> "flag & OBJECT_INFO_FOR_PREFETCH" means that OBJECT_INFO_QUICK also implies
>> OBJECT_INFO_FOR_PREFETCH.
>>
>> Split out the single bit from OBJECT_INFO_FOR_PREFETCH into a new
>> OBJECT_INFO_SKIP_FETCH_OBJECT as the single bit and keep
>> OBJECT_INFO_FOR_PREFETCH as the union of two flags. This allows a clearer use
>> of flag checking while also keeping the implication of OBJECT_INFO_QUICK.
>
> Oof. I actually suggested splitting these up for review, but thought it
> was only a clarity/flexibility issue, and completely missed the
> correctness aspect of checking when the bit is set.
>
> I agree with Junio's other response that using "==" would be the right
> way for a multi-bit check, in general. But I like the split here,
> because I think the result is more clear to read and harder to get
> wrong for future checks.
Thanks, for the feedback, both of you.
> I'd even go so far as to say...
>
>> + * This is meant for bulk prefetching of missing blobs in a partial
>> + * clone. Implies OBJECT_INFO_SKIP_FETCH_OBJECT and OBJECT_INFO_QUICK
>> + */
>> +#define OBJECT_INFO_FOR_PREFETCH (OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_QUICK)
>
> we could dump this, and callers should just say what they mean (i.e.,
> specify both flags).
Dropping the _PREFETCH flag also makes oid_object_info_extended() slightly
less "coupled" to the prefetch feature, and instead describes more explicitly
the way the flag is changing the behavior of the method.
> There are only two of them, and I think both would be more readable with
> a helper more like:
>
> int should_prefetch_object(struct repository *r,
> const struct object_id *oid) {
> return !oid_object_info_extended(r, oid, NULL,
> OBJECT_INFO_SKIP_FETCH_OBJECT |
> OBJECT_INFO_QUICK);
> }
>
> but unless everybody is immediately on-board with "yes, that is much
> nicer", I don't want bikeshedding to hold up your important and
> obviously-correct fix.
I'll come back with another series to drop the _PREFETCH flag after the
release calms down. It can give more time for others to chime in here.
Thanks, Junio for the quick turnaround in taking the patch.
Thanks,
-Stolee
prev parent reply other threads:[~2019-05-29 0:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 15:19 [PATCH 0/1] sha1-file: split OBJECT_INFO_FOR_PREFETCH Derrick Stolee via GitGitGadget
2019-05-28 15:19 ` [PATCH 1/1] " Derrick Stolee via GitGitGadget
2019-05-28 20:31 ` Junio C Hamano
2019-05-28 20:54 ` Jeff King
2019-05-29 0:29 ` Derrick Stolee [this message]
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