From: Jeff King <peff@peff•net>
To: "René Scharfe" <l.s.r@web•de>
Cc: Git List <git@vger•kernel.org>
Subject: Re: [PATCH 2/3] prio-queue: add prio_queue_replace()
Date: Sat, 19 Jul 2025 03:02:29 -0400 [thread overview]
Message-ID: <20250719070229.GF705356@coredump.intra.peff.net> (raw)
In-Reply-To: <4ed087c9-0229-4219-8cbd-55f9ee79ca35@web.de>
On Thu, Jul 17, 2025 at 11:20:53AM +0200, René Scharfe wrote:
> > I thought about building this optimization into prio_queue_get(), but
> > that would require prio_queue_peek() and prio_queue_put() to be adjusted
> > as well and all prio_queue users would have to be either made aware of
> > the not-fully-heapified state, or prevented from accessing prio_queue
> > properties like .nr and .array.
>
> Here's what that would like like. .nr and .array elements are kept
> consistent at all times, but the root item is not in heap order after a
> prio_queue_get(). That's good enough to enumerate all prio_queue items
> like commit-reach.c::queue_has_nonstale() or
> negotiator/skipping.c::push_parent() do.
Hmm, I agree that _probably_ we'd be fine as long as .nr and .array were
always consistent. It does make me feel a bit dirty to violate the heap
property in a way that callers can see. I guess the argument in favor of
it would be:
- if you are directly walking over all elements, then almost all
ordering is out the window. Yes, the root item is supposed to be the
min, but in a heap the rest of the elements won't be sorted.
- if you really want things in order from a heap, you'll be calling
the get() or peek() accessors. And that gives us an opportunity to
lazily put things in order.
I guess one alternative would be to make the array private and require
some kind of foreach accessor. True struct-field privacy in C sucks.
You have to hide behind a pointer, so there's runtime cost, plus
iteration requires a clunky callback rather than a loop. I guess we
could call it "array_" or something, and provide a foreach macro.
I dunno. I'm on the fence.
-Peff
next prev parent reply other threads:[~2025-07-19 7:02 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-15 14:35 [PATCH 0/3] commit: convert pop_most_recent_commit() to prio_queue René Scharfe
2025-07-15 14:51 ` [PATCH 1/3] " René Scharfe
2025-07-15 19:23 ` Junio C Hamano
2025-07-15 20:47 ` Justin Tobler
2025-07-16 9:39 ` René Scharfe
2025-07-16 5:05 ` Jeff King
2025-07-16 9:39 ` René Scharfe
2025-07-17 8:22 ` René Scharfe
2025-07-19 6:55 ` Jeff King
2025-07-19 6:57 ` Jeff King
2025-07-19 11:15 ` René Scharfe
2025-07-20 0:03 ` Jeff King
2025-07-20 1:22 ` Junio C Hamano
2025-07-16 22:23 ` Junio C Hamano
2025-07-17 8:22 ` René Scharfe
2025-07-15 14:51 ` [PATCH 2/3] prio-queue: add prio_queue_replace() René Scharfe
2025-07-16 5:09 ` Jeff King
2025-07-16 9:38 ` René Scharfe
2025-07-17 9:20 ` René Scharfe
2025-07-19 7:02 ` Jeff King [this message]
2025-07-15 14:51 ` [PATCH 3/3] commit: use prio_queue_replace() in pop_most_recent_commit() René Scharfe
2025-07-15 20:43 ` Junio C Hamano
2025-07-16 9:38 ` René Scharfe
2025-07-16 0:07 ` [PATCH 0/3] commit: convert pop_most_recent_commit() to prio_queue Junio C Hamano
2025-07-16 5:15 ` Jeff King
2025-07-16 9:38 ` René Scharfe
2025-07-19 6:45 ` Jeff King
2025-07-16 14:49 ` Junio C Hamano
2025-07-18 9:09 ` [PATCH v2 " René Scharfe
2025-07-18 9:39 ` [PATCH v2 1/3] " René Scharfe
2025-07-21 14:02 ` Lidong Yan
2025-08-03 9:54 ` René Scharfe
2025-08-03 16:48 ` Junio C Hamano
2025-08-04 19:56 ` René Scharfe
2025-07-18 9:39 ` [PATCH v2 3/3] commit: use prio_queue_replace() in pop_most_recent_commit(),MIME-Version: 1.0 René Scharfe
2025-08-03 11:12 ` Johannes Schindelin
2025-08-03 11:33 ` René Scharfe
2025-07-18 9:39 ` [PATCH v2 2/3] prio-queue: add prio_queue_replace() René Scharfe
2025-07-19 7:04 ` [PATCH v2 0/3] commit: convert pop_most_recent_commit() to prio_queue Jeff King
2025-07-22 6:26 ` SZEDER Gábor
2025-07-22 14:27 ` Junio C Hamano
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