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From: Jeff King <peff@peff.net>
To: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH v3 1/7] prio-queue: add 'peek' operation
Date: Thu, 11 Oct 2018 09:54:59 -0400	[thread overview]
Message-ID: <20181011135459.GA27312@sigill.intra.peff.net> (raw)
In-Reply-To: <cc1ec4c2702d8ba35873600d321015bb0430d92e.1537551564.git.gitgitgadget@gmail.com>

On Fri, Sep 21, 2018 at 10:39:27AM -0700, Derrick Stolee via GitGitGadget wrote:

> From: Derrick Stolee <dstolee@microsoft.com>
> 
> When consuming a priority queue, it can be convenient to inspect
> the next object that will be dequeued without actually dequeueing
> it. Our existing library did not have such a 'peek' operation, so
> add it as prio_queue_peek().

Makes sense.

> +void *prio_queue_peek(struct prio_queue *queue)
> +{
> +	if (!queue->nr)
> +		return NULL;
> +	if (!queue->compare)
> +		return queue->array[queue->nr - 1].data;
> +	return queue->array[0].data;

The non-compare version of get() treats this like a LIFO, and you do the
same here. Looks good.

In theory get() could be implemented in terms of peek(), but the result
is not actually shorter because we have to check those same conditions
to decide how to remove the item anyway.

> diff --git a/t/helper/test-prio-queue.c b/t/helper/test-prio-queue.c
> index 9807b649b1..e817bbf464 100644
> --- a/t/helper/test-prio-queue.c
> +++ b/t/helper/test-prio-queue.c
> @@ -22,9 +22,13 @@ int cmd__prio_queue(int argc, const char **argv)
>  	struct prio_queue pq = { intcmp };
>  
>  	while (*++argv) {
> -		if (!strcmp(*argv, "get"))
> -			show(prio_queue_get(&pq));
> -		else if (!strcmp(*argv, "dump")) {
> +		if (!strcmp(*argv, "get")) {
> +			void *peek = prio_queue_peek(&pq);
> +			void *get = prio_queue_get(&pq);
> +			if (peek != get)
> +				BUG("peek and get results do not match");
> +			show(get);
> +		} else if (!strcmp(*argv, "dump")) {

This is a nice cheap way of piggy-backing on the existing get tests.

-Peff

  parent reply	other threads:[~2018-10-11 13:55 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-27 20:41 [PATCH 0/6] Use generation numbers for --topo-order Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 1/6] prio-queue: add 'peek' operation Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 2/6] test-reach: add run_three_modes method Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 3/6] test-reach: add rev-list tests Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 4/6] revision.c: begin refactoring --topo-order logic Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 5/6] commit/revisions: bookkeeping before refactoring Derrick Stolee via GitGitGadget
2018-08-27 20:41 ` [PATCH 6/6] revision.c: refactor basic topo-order logic Derrick Stolee via GitGitGadget
2018-08-27 21:23 ` [PATCH 0/6] Use generation numbers for --topo-order Junio C Hamano
2018-09-18  4:08 ` [PATCH v2 " Derrick Stolee via GitGitGadget
2018-09-18  4:08   ` [PATCH v2 1/6] prio-queue: add 'peek' operation Derrick Stolee via GitGitGadget
2018-09-18  4:08   ` [PATCH v2 2/6] test-reach: add run_three_modes method Derrick Stolee via GitGitGadget
2018-09-18 18:02     ` SZEDER Gábor
2018-09-19 19:31       ` Junio C Hamano
2018-09-19 19:38         ` Junio C Hamano
2018-09-20 21:18           ` Junio C Hamano
2018-09-18  4:08   ` [PATCH v2 3/6] test-reach: add rev-list tests Derrick Stolee via GitGitGadget
2018-09-18  4:08   ` [PATCH v2 4/6] revision.c: begin refactoring --topo-order logic Derrick Stolee via GitGitGadget
2018-09-18  4:08   ` [PATCH v2 5/6] commit/revisions: bookkeeping before refactoring Derrick Stolee via GitGitGadget
2018-09-18  4:08   ` [PATCH v2 6/6] revision.c: refactor basic topo-order logic Derrick Stolee via GitGitGadget
2018-09-18  5:51     ` Ævar Arnfjörð Bjarmason
2018-09-18  6:05   ` [PATCH v2 0/6] Use generation numbers for --topo-order Ævar Arnfjörð Bjarmason
2018-09-21 15:47     ` Derrick Stolee
2018-09-21 17:39   ` [PATCH v3 0/7] " Derrick Stolee via GitGitGadget
2018-09-21 17:39     ` [PATCH v3 1/7] prio-queue: add 'peek' operation Derrick Stolee via GitGitGadget
2018-09-26 19:15       ` Derrick Stolee
2018-10-11 13:54       ` Jeff King [this message]
2018-09-21 17:39     ` [PATCH v3 2/7] test-reach: add run_three_modes method Derrick Stolee via GitGitGadget
2018-10-11 13:57       ` Jeff King
2018-09-21 17:39     ` [PATCH v3 3/7] test-reach: add rev-list tests Derrick Stolee via GitGitGadget
2018-10-11 13:58       ` Jeff King
2018-10-12  4:34         ` Junio C Hamano
2018-09-21 17:39     ` [PATCH v3 4/7] revision.c: begin refactoring --topo-order logic Derrick Stolee via GitGitGadget
2018-10-11 14:06       ` Jeff King
2018-10-12  6:33       ` Junio C Hamano
2018-10-12 12:32         ` Derrick Stolee
2018-10-12 16:15         ` Johannes Sixt
2018-10-13  8:05           ` Junio C Hamano
2018-09-21 17:39     ` [PATCH v3 5/7] commit/revisions: bookkeeping before refactoring Derrick Stolee via GitGitGadget
2018-10-11 14:21       ` Jeff King
2018-09-21 17:39     ` [PATCH v3 6/7] revision.h: add whitespace in flag definitions Derrick Stolee via GitGitGadget
2018-09-21 17:39     ` [PATCH v3 7/7] revision.c: refactor basic topo-order logic Derrick Stolee via GitGitGadget
2018-09-27 17:57       ` Derrick Stolee
2018-10-06 16:56         ` Jakub Narebski
2018-10-11 15:35       ` Jeff King
2018-10-11 16:21         ` Derrick Stolee
2018-10-25  9:43           ` Jeff King
2018-10-25 13:00             ` Derrick Stolee
2018-10-11 22:32       ` Stefan Beller
2018-09-21 21:22     ` [PATCH v3 0/7] Use generation numbers for --topo-order Junio C Hamano
2018-10-16 22:36     ` [PATCH v4 " Derrick Stolee via GitGitGadget
2018-10-16 22:36       ` [PATCH v4 1/7] prio-queue: add 'peek' operation Derrick Stolee via GitGitGadget
2018-10-16 22:36       ` [PATCH v4 2/7] test-reach: add run_three_modes method Derrick Stolee via GitGitGadget
2018-10-16 22:36       ` [PATCH v4 3/7] test-reach: add rev-list tests Derrick Stolee via GitGitGadget
2018-10-21 10:21         ` Jakub Narebski
2018-10-21 15:28           ` Derrick Stolee
2018-10-16 22:36       ` [PATCH v4 4/7] revision.c: begin refactoring --topo-order logic Derrick Stolee via GitGitGadget
2018-10-21 15:55         ` Jakub Narebski
2018-10-22  1:12           ` Junio C Hamano
2018-10-22  1:51             ` Derrick Stolee
2018-10-22  1:55               ` [RFC PATCH] revision.c: use new algorithm in A..B case Derrick Stolee
2018-10-25  8:28               ` [PATCH v4 4/7] revision.c: begin refactoring --topo-order logic Junio C Hamano
2018-10-26 20:56                 ` Jakub Narebski
2018-10-16 22:36       ` [PATCH v4 5/7] commit/revisions: bookkeeping before refactoring Derrick Stolee via GitGitGadget
2018-10-21 21:17         ` Jakub Narebski
2018-10-16 22:36       ` [PATCH v4 6/7] revision.c: generation-based topo-order algorithm Derrick Stolee via GitGitGadget
2018-10-22 13:37         ` Jakub Narebski
2018-10-23 13:54           ` Derrick Stolee
2018-10-26 16:55             ` Jakub Narebski
2018-10-16 22:36       ` [PATCH v4 7/7] t6012: make rev-list tests more interesting Derrick Stolee via GitGitGadget
2018-10-23 15:48         ` Jakub Narebski
2018-10-21 12:57       ` [PATCH v4 0/7] Use generation numbers for --topo-order Jakub Narebski
2018-11-01  5:21       ` Junio C Hamano
2018-11-01 13:49         ` Derrick Stolee
2018-11-01 23:54           ` Junio C Hamano
2018-11-01 13:46       ` [PATCH v5 " Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 1/7] prio-queue: add 'peek' operation Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 2/7] test-reach: add run_three_modes method Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 3/7] test-reach: add rev-list tests Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 4/7] revision.c: begin refactoring --topo-order logic Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 5/7] commit/revisions: bookkeeping before refactoring Derrick Stolee
2018-11-01 13:46         ` [PATCH v5 6/7] revision.c: generation-based topo-order algorithm Derrick Stolee
2018-11-01 15:48           ` SZEDER Gábor
2018-11-01 16:12             ` Derrick Stolee
2019-11-08  2:50           ` Mike Hommey
2019-11-11  1:07             ` Derrick Stolee
2019-11-18 23:04               ` SZEDER Gábor
2018-11-01 13:46         ` [PATCH v5 7/7] t6012: make rev-list tests more interesting Derrick Stolee

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