Re: [PATCH 1/2] pack-objects: break out of want_object loop early
- From
Jeff King <peff@peff.net>
- Date
- Jul 26, 2016, 20:48 UTC
- Message-ID
- <20160726204851.GA22353@sigill.intra.peff.net>
- In-Reply-To
- <xmqqshuwyw14.fsf@gitster.mtv.corp.google.com>
On Tue, Jul 26, 2016 at 01:38:47PM -0700, Junio C Hamano wrote:
Show 24 quoted lines
> Jeff King <peff@peff.net> writes: > > >> I do not mind too much about having to check two bools twice. But > >> given that the reason why I was confused was because I didn't see > >> why we need to pass the two "return 0" conditions at least once > >> before we decide that we do not need the "return 0" thing at all, > >> and started constructing a case where this might break by writing > >> "Suppose you have two packs, one remote and one local in packed_git > >> list in this order, and ..." before I realized that the new "early > >> break" can be hoisted up like the above, I definitely feel that "we > >> found one, and we aren't conditionally pretending that this thing > >> does not need to be packed at all, so return early and say we want > >> to pack it" is easier to understand before the two existing "if" > >> statements. > > > > Ah, right. Now you had me second-guessing for a moment that there might > > be a bad case in hoisting it up where we would want to return 0 but > > would break out early to the "return 1". > > > > But it cannot be the case, because the break is mutually exclusive with > > the two conditions. > > Here is what I amended looks like (with s/local/non-local/ in the > log message).
Thanks, I was actually just preparing a very similar patch (to move the condition and to add a comment, since clearly it is tricky).
I got side-tracked by adding a t/perf test to show off the improvement. It's rather tricky to get right and takes a long time to run. I _think_ I have it now, but am waiting for results. :)
Show 23 quoted lines
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c > index a2f8cfd..a46bf5b 100644 > --- a/builtin/pack-objects.c > +++ b/builtin/pack-objects.c > @@ -977,6 +977,21 @@ static int want_object_in_pack(const unsigned char *sha1, > return 1; > if (incremental) > return 0; > + > + /* > + * When asked to do --local (do not include an > + * object that appears in a pack we borrow > + * from elsewhere) or --honor-pack-keep (do not > + * include an object that appears in a pack marked > + * with .keep), we need to make sure no copy of this > + * object come from in _any_ pack that causes us to > + * omit it, and need to complete this loop. When > + * neither option is in effect, we know the object > + * we just found is going to be packed, so break > + * out of the loop to return 1 now. > + */ > + if (!ignore_packed_keep && !local) > + break;
This looks great. Given the explanation in the comment, it might be more clear to switch the break to "return 1", but I could go either way.
-Peff