revision: use priority queue for non-limited streaming walks

The streaming (non-limited) walk in get_revision_1() inserts newly
discovered parent commits into a date-sorted queue via
commit_list_insert_by_date(), which scans the linked list to find the
insertion point -- O(w) per insert, where w is the width of the active
walk frontier.  Replace this with an O(log w) priority queue.

Add a commit_queue field to rev_info alongside the existing commits
linked list.  The two representations are mutually exclusive: setup
and external callers that need list access use the linked list, then
get_revision_1() lazily drains it into the priority queue on first
call.  Add a REV_WALK_NO_WALK enum value to distinguish the no_walk
case (which still uses the commit list) from the streaming case.

The conversion function rev_info_commit_list_to_queue() is public so
callers that know they will iterate can convert early.

Combined with the limit_list() priority queue change already in
master, this eliminates all O(w) sorted linked-list insertion from
the revision walk machinery.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 13 deletions

diff --git a/commit.c b/commit.c
index e3e7352e69..5112c7b2af 100644
--- a/commit.c
+++ b/commit.c
@@ -729,19 +729,6 @@ void commit_list_free(struct commit_list *list)
 		pop_commit(&list);
 }
 
-struct commit_list * commit_list_insert_by_date(struct commit *item, struct commit_list **list)
-{
-	struct commit_list **pp = list;
-	struct commit_list *p;
-	while ((p = *pp) != NULL) {
-		if (p->item->date < item->date) {
-			break;
-		}
-		pp = &p->next;
-	}
-	return commit_list_insert(item, pp);
-}
-
 static int commit_list_compare_by_date(const struct commit_list *a,
 				       const struct commit_list *b)
 {