Add "named object array" concept

We've had this notion of a "object_list" for a long time, which eventually
grew a "name" member because some users (notably git-rev-list) wanted to
name each object as it is generated.

That object_list is great for some things, but it isn't all that wonderful
for others, and the "name" member is generally not used by everybody.

This patch splits the users of the object_list array up into two: the
traditional list users, who want the list-like format, and who don't
actually use or want the name. And another class of users that really used
the list as an extensible array, and generally wanted to name the objects.

The patch is fairly straightforward, but it's also biggish. Most of it
really just cleans things up: switching the revision parsing and listing
over to the array makes things like the builtin-diff usage much simpler
(we now see exactly how many members the array has, and we don't get the
objects reversed from the order they were on the command line).

One of the main reasons for doing this at all is that the malloc overhead
of the simple object list was actually pretty high, and the array is just
a lot denser. So this patch brings down memory usage by git-rev-list by
just under 3% (on top of all the other memory use optimizations) on the
mozilla archive.

It does add more lines than it removes, and more importantly, it adds a
whole new infrastructure for maintaining lists of objects, but on the
other hand, the new dynamic array code is pretty obvious. The change to
builtin-diff-tree.c shows a fairly good example of why an array interface
is sometimes more natural, and just much simpler for everybody.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 15 insertions, 18 deletions

diff --git a/revision.c b/revision.c
index 7bff2a10b..b963f2adf 100644
--- a/revision.c
+++ b/revision.c
@@ -31,17 +31,12 @@ static char *path_name(struct name_path *path, const char *name)
 	return n;
 }
 
-struct object_list **add_object(struct object *obj,
-				       struct object_list **p,
-				       struct name_path *path,
-				       const char *name)
+void add_object(struct object *obj,
+		struct object_array *p,
+		struct name_path *path,
+		const char *name)
 {
-	struct object_list *entry = xmalloc(sizeof(*entry));
-	entry->item = obj;
-	entry->next = *p;
-	entry->name = path_name(path, name);
-	*p = entry;
-	return &entry->next;
+	add_object_array(obj, path_name(path, name), p);
 }
 
 static void mark_blob_uninteresting(struct blob *blob)
@@ -117,9 +112,9 @@ void mark_parents_uninteresting(struct commit *commit)
 	}
 }
 
-static void add_pending_object(struct rev_info *revs, struct object *obj, const char *name)
+void add_pending_object(struct rev_info *revs, struct object *obj, const char *name)
 {
-	add_object(obj, &revs->pending_objects, NULL, name);
+	add_object_array(obj, name, &revs->pending);
 }
 
 static struct object *get_reference(struct rev_info *revs, const char *name, const unsigned char *sha1, unsigned int flags)
@@ -836,7 +831,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 		object = get_reference(revs, arg, sha1, flags ^ local_flags);
 		add_pending_object(revs, object, arg);
 	}
-	if (def && !revs->pending_objects) {
+	if (def && !revs->pending.nr) {
 		unsigned char sha1[20];
 		struct object *object;
 		if (get_sha1(def, sha1))
@@ -868,11 +863,13 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 
 void prepare_revision_walk(struct rev_info *revs)
 {
-	struct object_list *list;
+	int nr = revs->pending.nr;
+	struct object_array_entry *list = revs->pending.objects;
 
-	list = revs->pending_objects;
-	revs->pending_objects = NULL;
-	while (list) {
+	revs->pending.nr = 0;
+	revs->pending.alloc = 0;
+	revs->pending.objects = NULL;
+	while (--nr >= 0) {
 		struct commit *commit = handle_commit(revs, list->item, list->name);
 		if (commit) {
 			if (!(commit->object.flags & SEEN)) {
@@ -880,7 +877,7 @@ void prepare_revision_walk(struct rev_info *revs)
 				insert_by_date(commit, &revs->commits);
 			}
 		}
-		list = list->next;
+		list++;
 	}
 
 	if (revs->no_walk)