Merge branch 'jk/stable-prio-queue'

* jk/stable-prio-queue:
  t5539: update a flaky test
  paint_down_to_common: use prio_queue
  prio-queue: make output stable with respect to insertion
  prio-queue: factor out compare and swap operations

4 files changed, 60 insertions, 51 deletions

diff --git a/commit.c b/commit.c
index dce3d69dfd..2274e43fdf 100644
--- a/commit.c
+++ b/commit.c
@@ -764,45 +764,41 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
 
 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
 
-static struct commit *interesting(struct commit_list *list)
+static int queue_has_nonstale(struct prio_queue *queue)
 {
-	while (list) {
-		struct commit *commit = list->item;
-		list = list->next;
-		if (commit->object.flags & STALE)
-			continue;
-		return commit;
+	int i;
+	for (i = 0; i < queue->nr; i++) {
+		struct commit *commit = queue->array[i].data;
+		if (!(commit->object.flags & STALE))
+			return 1;
 	}
-	return NULL;
+	return 0;
 }
 
 /* all input commits in one and twos[] must have been parsed! */
 static struct commit_list *paint_down_to_common(struct commit *one, int n, struct commit **twos)
 {
-	struct commit_list *list = NULL;
+	struct prio_queue queue = { compare_commits_by_commit_date };
 	struct commit_list *result = NULL;
 	int i;
 
 	one->object.flags |= PARENT1;
-	commit_list_insert_by_date(one, &list);
-	if (!n)
-		return list;
+	if (!n) {
+		commit_list_append(one, &result);
+		return result;
+	}
+	prio_queue_put(&queue, one);
+
 	for (i = 0; i < n; i++) {
 		twos[i]->object.flags |= PARENT2;
-		commit_list_insert_by_date(twos[i], &list);
+		prio_queue_put(&queue, twos[i]);
 	}
 
-	while (interesting(list)) {
-		struct commit *commit;
+	while (queue_has_nonstale(&queue)) {
+		struct commit *commit = prio_queue_get(&queue);
 		struct commit_list *parents;
-		struct commit_list *next;
 		int flags;
 
-		commit = list->item;
-		next = list->next;
-		free(list);
-		list = next;
-
 		flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
 		if (flags == (PARENT1 | PARENT2)) {
 			if (!(commit->object.flags & RESULT)) {
@@ -821,11 +817,11 @@ static struct commit_list *paint_down_to_common(struct commit *one, int n, struc
 			if (parse_commit(p))
 				return NULL;
 			p->object.flags |= flags;
-			commit_list_insert_by_date(p, &list);
+			prio_queue_put(&queue, p);
 		}
 	}
 
-	free_commit_list(list);
+	clear_prio_queue(&queue);
 	return result;
 }
 
diff --git a/prio-queue.c b/prio-queue.c
index c9f8c6d253..e4365b00d6 100644
--- a/prio-queue.c
+++ b/prio-queue.c
@@ -1,18 +1,30 @@
 #include "cache.h"
-#include "commit.h"
 #include "prio-queue.h"
 
+static inline int compare(struct prio_queue *queue, int i, int j)
+{
+	int cmp = queue->compare(queue->array[i].data, queue->array[j].data,
+				 queue->cb_data);
+	if (!cmp)
+		cmp = queue->array[i].ctr - queue->array[j].ctr;
+	return cmp;
+}
+
+static inline void swap(struct prio_queue *queue, int i, int j)
+{
+	struct prio_queue_entry tmp = queue->array[i];
+	queue->array[i] = queue->array[j];
+	queue->array[j] = tmp;
+}
+
 void prio_queue_reverse(struct prio_queue *queue)
 {
 	int i, j;
 
 	if (queue->compare != NULL)
 		die("BUG: prio_queue_reverse() on non-LIFO queue");
-	for (i = 0; i <= (j = (queue->nr - 1) - i); i++) {
-		struct commit *swap = queue->array[i];
-		queue->array[i] = queue->array[j];
-		queue->array[j] = swap;
-	}
+	for (i = 0; i <= (j = (queue->nr - 1) - i); i++)
+		swap(queue, i, j);
 }
 
 void clear_prio_queue(struct prio_queue *queue)
@@ -21,44 +33,42 @@ void clear_prio_queue(struct prio_queue *queue)
 	queue->nr = 0;
 	queue->alloc = 0;
 	queue->array = NULL;
+	queue->insertion_ctr = 0;
 }
 
 void prio_queue_put(struct prio_queue *queue, void *thing)
 {
-	prio_queue_compare_fn compare = queue->compare;
 	int ix, parent;
 
 	/* Append at the end */
 	ALLOC_GROW(queue->array, queue->nr + 1, queue->alloc);
-	queue->array[queue->nr++] = thing;
-	if (!compare)
+	queue->array[queue->nr].ctr = queue->insertion_ctr++;
+	queue->array[queue->nr].data = thing;
+	queue->nr++;
+	if (!queue->compare)
 		return; /* LIFO */
 
 	/* Bubble up the new one */
 	for (ix = queue->nr - 1; ix; ix = parent) {
 		parent = (ix - 1) / 2;
-		if (compare(queue->array[parent], queue->array[ix],
-			    queue->cb_data) <= 0)
+		if (compare(queue, parent, ix) <= 0)
 			break;
 
-		thing = queue->array[parent];
-		queue->array[parent] = queue->array[ix];
-		queue->array[ix] = thing;
+		swap(queue, parent, ix);
 	}
 }
 
 void *prio_queue_get(struct prio_queue *queue)
 {
-	void *result, *swap;
+	void *result;
 	int ix, child;
-	prio_queue_compare_fn compare = queue->compare;
 
 	if (!queue->nr)
 		return NULL;
-	if (!compare)
-		return queue->array[--queue->nr]; /* LIFO */
+	if (!queue->compare)
+		return queue->array[--queue->nr].data; /* LIFO */
 
-	result = queue->array[0];
+	result = queue->array[0].data;
 	if (!--queue->nr)
 		return result;
 
@@ -67,18 +77,14 @@ void *prio_queue_get(struct prio_queue *queue)
 	/* Push down the one at the root */
 	for (ix = 0; ix * 2 + 1 < queue->nr; ix = child) {
 		child = ix * 2 + 1; /* left */
-		if ((child + 1 < queue->nr) &&
-		    (compare(queue->array[child], queue->array[child + 1],
-			     queue->cb_data) >= 0))
+		if (child + 1 < queue->nr &&
+		    compare(queue, child, child + 1) >= 0)
 			child++; /* use right child */
 
-		if (compare(queue->array[ix], queue->array[child],
-			    queue->cb_data) <= 0)
+		if (compare(queue, ix, child) <= 0)
 			break;
 
-		swap = queue->array[child];
-		queue->array[child] = queue->array[ix];
-		queue->array[ix] = swap;
+		swap(queue, child, ix);
 	}
 	return result;
 }
diff --git a/prio-queue.h b/prio-queue.h
index 9c3cd1f875..d030ec9dd6 100644
--- a/prio-queue.h
+++ b/prio-queue.h
@@ -21,11 +21,17 @@
  */
 typedef int (*prio_queue_compare_fn)(const void *one, const void *two, void *cb_data);
 
+struct prio_queue_entry {
+	unsigned ctr;
+	void *data;
+};
+
 struct prio_queue {
 	prio_queue_compare_fn compare;
+	unsigned insertion_ctr;
 	void *cb_data;
 	int alloc, nr;
-	void **array;
+	struct prio_queue_entry *array;
 };
 
 /*
diff --git a/t/t5539-fetch-http-shallow.sh b/t/t5539-fetch-http-shallow.sh
index 94553e1039..b46118846c 100755
--- a/t/t5539-fetch-http-shallow.sh
+++ b/t/t5539-fetch-http-shallow.sh
@@ -54,6 +54,7 @@ EOF
 test_expect_success 'no shallow lines after receiving ACK ready' '
 	(
 		cd shallow &&
+		test_tick &&
 		for i in $(test_seq 15)
 		do
 			git checkout --orphan unrelated$i &&