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prio-queue: add 'peek' operation

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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().

Add a reference-level comparison in t/helper/test-prio-queue.c
so this method is exercised by t0009-prio-queue.sh. Further, add
a test that checks the behavior when the compare function is NULL
(i.e. the queue becomes a stack).

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee
2018-11-01 13:46:17 +00:00
committed by Junio C Hamano
parent 2d3b1c576c
commit aca4240f6a
4 changed files with 47 additions and 8 deletions
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6
prio-queue.h
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@ -46,6 +46,12 @@ extern void prio_queue_put(struct prio_queue *, void *thing);
*/
extern void *prio_queue_get(struct prio_queue *);
/*
* Gain access to the "thing" that would be returned by
* prio_queue_get, but do not remove it from the queue.
*/
extern void *prio_queue_peek(struct prio_queue *);
extern void clear_prio_queue(struct prio_queue *);
/* Reverse the LIFO elements */