On Fri, Sep 21, 2018 at 10:39:27AM -0700, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
>
> 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
