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@xxxxxxxxxxxxx>
---
prio-queue.c | 9 +++++++++
prio-queue.h | 6 ++++++
t/helper/test-prio-queue.c | 26 ++++++++++++++++++--------
t/t0009-prio-queue.sh | 14 ++++++++++++++
4 files changed, 47 insertions(+), 8 deletions(-)
diff --git a/prio-queue.c b/prio-queue.c
index a078451872..d3f488cb05 100644
--- a/prio-queue.c
+++ b/prio-queue.c
@@ -85,3 +85,12 @@ void *prio_queue_get(struct prio_queue *queue)
}
return result;
}
+
+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;
+}
diff --git a/prio-queue.h b/prio-queue.h
index d030ec9dd6..682e51867a 100644
--- a/prio-queue.h
+++ b/prio-queue.h
@@ -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 */
diff --git a/t/helper/test-prio-queue.c b/t/helper/test-prio-queue.c
index 9807b649b1..5bc9c46ea5 100644
--- a/t/helper/test-prio-queue.c
+++ b/t/helper/test-prio-queue.c
@@ -22,14 +22,24 @@ 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")) {
- int *v;
- while ((v = prio_queue_get(&pq)))
- show(v);
- }
- else {
+ 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")) {
+ void *peek;
+ void *get;
+ while ((peek = prio_queue_peek(&pq))) {
+ get = prio_queue_get(&pq);
+ if (peek != get)
+ BUG("peek and get results do not match");
+ show(get);
+ }
+ } else if (!strcmp(*argv, "stack")) {
+ pq.compare = NULL;
+ } else {
int *v = malloc(sizeof(*v));
*v = atoi(*argv);
prio_queue_put(&pq, v);
diff --git a/t/t0009-prio-queue.sh b/t/t0009-prio-queue.sh
index e56dfce668..3941ad2528 100755
--- a/t/t0009-prio-queue.sh
+++ b/t/t0009-prio-queue.sh
@@ -47,4 +47,18 @@ test_expect_success 'notice empty queue' '
test_cmp expect actual
'
+cat >expect <<'EOF'
+3
+2
+6
+4
+5
+1
+8
+EOF
+test_expect_success 'stack order' '
+ test-tool prio-queue stack 8 1 5 4 6 2 3 dump >actual &&
+ test_cmp expect actual
+'
+
test_done
base-commit: 2d3b1c576c85b7f5db1f418907af00ab88e0c303
--
2.19.1.542.gc4df23f792
