Rewrite the Revision Walker

The new revision walker uses an internal Commit object storage system,
custom memory allocator and much improved topological and time sorting
algorithms. It's about 20x times faster than the previous implementation
when browsing big repositories.

The following external API calls have changed:

	`git_revwalk_next` returns an OID instead of a full commit object.
	The initial call to `git_revwalk_next` is no longer blocking when
	iterating through a repo with a time-sorting mode.

	Iterating with Topological or inverted modes still makes the initial
	call blocking to preprocess the commit list, but this block should be
	mostly unnoticeable on most repositories (topological preprocessing
	times at 0.3s on the git.git repo).

	`git_revwalk_push` and `git_revwalk_hide` now take an OID instead
	of a full commit object.

1 files changed, 363 insertions, 255 deletions

diff --git a/src/revwalk.c b/src/revwalk.c
index a1cd0ebb7..edafbe73d 100644
--- a/src/revwalk.c
+++ b/src/revwalk.c
@@ -27,22 +27,132 @@
 #include "commit.h"
 #include "revwalk.h"
 #include "hashtable.h"
+#include "pqueue.h"
 
-uint32_t git_revwalk__commit_hash(const void *key, int hash_id)
+typedef struct commit_object {
+	git_oid oid;
+	uint32_t time;
+	unsigned int seen:1,
+			 uninteresting:1,
+			 topo_delay:1,
+			 parsed:1;
+
+	unsigned short in_degree;
+	unsigned short out_degree;
+
+	struct commit_object **parents;
+} commit_object;
+
+typedef struct commit_list {
+	commit_object *item;
+	struct commit_list *next;
+} commit_list;
+
+struct git_revwalk {
+	git_repository *repo;
+
+	git_hashtable *commits;
+	git_vector pending;
+
+	commit_list *iterator_topo;
+	commit_list *iterator_rand;
+	commit_list *iterator_reverse;
+	git_pqueue iterator_time;
+
+	int (*get_next)(commit_object **, git_revwalk *);
+	int (*enqueue)(git_revwalk *, commit_object *);
+
+	git_vector memory_alloc;
+	size_t chunk_size;
+
+	unsigned walking:1;
+	unsigned int sorting;
+};
+
+commit_list *commit_list_insert(commit_object *item, commit_list **list_p)
+{
+	commit_list *new_list = git__malloc(sizeof(commit_list));
+	new_list->item = item;
+	new_list->next = *list_p;
+	*list_p = new_list;
+	return new_list;
+}
+
+void commit_list_free(commit_list *list)
+{
+	while (list) {
+		commit_list *temp = list;
+		list = temp->next;
+		free(temp);
+	}
+}
+
+commit_object *commit_list_pop(commit_list **stack)
+{
+	commit_list *top = *stack;
+	commit_object *item = top ? top->item : NULL;
+
+	if (top) {
+		*stack = top->next;
+		free(top);
+	}
+	return item;
+}
+
+static int commit_time_cmp(void *a, void *b)
+{
+	commit_object *commit_a = (commit_object *)a;
+	commit_object *commit_b = (commit_object *)b;
+
+	return (commit_a->time < commit_b->time);
+}
+
+static uint32_t object_table_hash(const void *key, int hash_id)
 {
 	uint32_t r;
-	git_commit *commit;
+	git_oid *id;
 
-	commit = (git_commit *)key;
-	memcpy(&r, commit->object.id.id + (hash_id * sizeof(uint32_t)), sizeof(r));
+	id = (git_oid *)key;
+	memcpy(&r, id->id + (hash_id * sizeof(uint32_t)), sizeof(r));
 	return r;
 }
 
-int git_revwalk__commit_keycmp(const void *key_a, const void *key_b)
+#define COMMITS_PER_CHUNK 128
+#define CHUNK_STEP 64
+#define PARENTS_PER_COMMIT ((CHUNK_STEP - sizeof(commit_object)) / sizeof(commit_object *))
+
+static int alloc_chunk(git_revwalk *walk)
 {
-	git_commit *a = (git_commit *)key_a;
-	git_commit *b = (git_commit *)key_b;
-	return git_oid_cmp(&a->object.id, &b->object.id);
+	void *chunk;
+
+	chunk = git__calloc(COMMITS_PER_CHUNK, CHUNK_STEP);
+	if (chunk == NULL)
+		return GIT_ENOMEM;
+
+	walk->chunk_size = 0;
+	return git_vector_insert(&walk->memory_alloc, chunk);
+}
+
+static commit_object *alloc_commit(git_revwalk *walk)
+{
+	unsigned char *chunk;
+
+	if (walk->chunk_size == COMMITS_PER_CHUNK)
+		alloc_chunk(walk);
+
+	chunk = git_vector_get(&walk->memory_alloc, walk->memory_alloc.length - 1);
+	chunk += (walk->chunk_size * CHUNK_STEP);
+	walk->chunk_size++;
+
+	return (commit_object *)chunk;
+}
+
+static commit_object **alloc_parents(commit_object *commit, size_t n_parents)
+{
+	if (n_parents <= PARENTS_PER_COMMIT)
+		return (commit_object **)((unsigned char *)commit + sizeof(commit_object));
+
+	return git__malloc(n_parents * sizeof(commit_object *));
 }
 
 int git_revwalk_new(git_revwalk **revwalk_out, git_repository *repo)
@@ -56,14 +166,18 @@ int git_revwalk_new(git_revwalk **revwalk_out, git_repository *repo)
 	memset(walk, 0x0, sizeof(git_revwalk));
 
 	walk->commits = git_hashtable_alloc(64,
-			git_revwalk__commit_hash,
-			git_revwalk__commit_keycmp);
+			object_table_hash,
+			(git_hash_keyeq_ptr)git_oid_cmp);
 
 	if (walk->commits == NULL) {
 		free(walk);
 		return GIT_ENOMEM;
 	}
 
+	git_vector_init(&walk->pending, 8, NULL);
+	git_vector_init(&walk->memory_alloc, 8, NULL);
+	alloc_chunk(walk);
+
 	walk->repo = repo;
 
 	*revwalk_out = walk;
@@ -72,11 +186,20 @@ int git_revwalk_new(git_revwalk **revwalk_out, git_repository *repo)
 
 void git_revwalk_free(git_revwalk *walk)
 {
+	unsigned int i;
+
 	if (walk == NULL)
 		return;
 
 	git_revwalk_reset(walk);
 	git_hashtable_free(walk->commits);
+	git_vector_free(&walk->pending);
+
+	for (i = 0; i < walk->memory_alloc.length; ++i) {
+		free(git_vector_get(&walk->memory_alloc, i));
+	}
+
+	git_vector_free(&walk->memory_alloc);
 	free(walk);
 }
 
@@ -98,364 +221,349 @@ int git_revwalk_sorting(git_revwalk *walk, unsigned int sort_mode)
 	return GIT_SUCCESS;
 }
 
-static git_revwalk_commit *commit_to_walkcommit(git_revwalk *walk, git_commit *commit_object)
+static commit_object *commit_lookup(git_revwalk *walk, const git_oid *oid)
 {
-	git_revwalk_commit *commit;
-
-	commit = (git_revwalk_commit *)git_hashtable_lookup(walk->commits, commit_object);
+	commit_object *commit;
 
-	if (commit != NULL)
+	if ((commit = git_hashtable_lookup(walk->commits, oid)) != NULL)
 		return commit;
 
-	commit = git__malloc(sizeof(git_revwalk_commit));
+	commit = alloc_commit(walk);
 	if (commit == NULL)
 		return NULL;
 
-	memset(commit, 0x0, sizeof(git_revwalk_commit));
-
-	commit->commit_object = commit_object;
-	GIT_OBJECT_INCREF(walk->repo, commit_object);
+	git_oid_cpy(&commit->oid, oid);
 
-	git_hashtable_insert(walk->commits, commit_object, commit);
+	if (git_hashtable_insert(walk->commits, &commit->oid, commit) < GIT_SUCCESS) {
+		free(commit);
+		return NULL;
+	}
 
 	return commit;
 }
 
-static git_revwalk_commit *insert_commit(git_revwalk *walk, git_commit *commit_object)
+static int commit_quick_parse(git_revwalk *walk, commit_object *commit, git_rawobj *raw)
 {
-	git_revwalk_commit *commit;
-	unsigned int i;
+	const int parent_len = STRLEN("parent ") + GIT_OID_HEXSZ + 1;
 
-	assert(walk && commit_object);
+	unsigned char *buffer = raw->data;
+	unsigned char *buffer_end = buffer + raw->len;
+	unsigned char *parents_start;
 
-	if (commit_object->object.repo != walk->repo || walk->walking)
-		return NULL;
+	int i, parents = 0;
 
-	commit = commit_to_walkcommit(walk, commit_object);
-	if (commit == NULL)
-		return NULL;
+	buffer += STRLEN("tree ") + GIT_OID_HEXSZ + 1;
 
-	if (commit->seen)
-		return commit;
+	parents_start = buffer;
+	while (buffer + parent_len < buffer_end && memcmp(buffer, "parent ", STRLEN("parent ")) == 0) {
+		parents++;
+		buffer += parent_len;
+	}
 
-	commit->seen = 1;
+	commit->parents = alloc_parents(commit, parents);
+	if (commit->parents == NULL)
+		return GIT_ENOMEM;
 
-	for (i = 0; i < commit->commit_object->parents.length; ++i) {
-		git_commit *parent_object;
-		git_revwalk_commit *parent;
+	buffer = parents_start;
+	for (i = 0; i < parents; ++i) {
+		git_oid oid;
 
-		parent_object = git_vector_get(&commit->commit_object->parents, i);
+		if (git_oid_mkstr(&oid, (char *)buffer + STRLEN("parent ")) < GIT_SUCCESS)
+			return GIT_EOBJCORRUPTED;
 
-		if ((parent = commit_to_walkcommit(walk, parent_object)) == NULL)
-			return NULL;
+		commit->parents[i] = commit_lookup(walk, &oid);
+		if (commit->parents[i] == NULL)
+			return GIT_ENOMEM;
 
-		parent = insert_commit(walk, parent_object);
-		if (parent == NULL)
-			return NULL;
+		buffer += parent_len;
+	}
 
-		parent->in_degree++;
+	commit->out_degree = (unsigned short)parents;
 
-		git_revwalk_list_push_back(&commit->parents, parent);
-	}
+	if ((buffer = memchr(buffer, '\n', buffer_end - buffer)) == NULL)
+		return GIT_EOBJCORRUPTED;
 
-	if (git_revwalk_list_push_back(&walk->iterator, commit))
-		return NULL;
+	buffer = memchr(buffer, '>', buffer_end - buffer);
+	if (buffer == NULL)
+		return GIT_EOBJCORRUPTED;
 
-	return commit;
-}
+	commit->time = strtol((char *)buffer + 2, NULL, 10);
+	if (commit->time == 0)
+		return GIT_EOBJCORRUPTED;
 
-int git_revwalk_push(git_revwalk *walk, git_commit *commit)
-{
-	assert(walk && commit);
-	return insert_commit(walk, commit) ? GIT_SUCCESS : GIT_ENOMEM;
+	commit->parsed = 1;
+	return GIT_SUCCESS;
 }
 
-static void mark_uninteresting(git_revwalk_commit *commit)
+static int commit_parse(git_revwalk *walk, commit_object *commit)
 {
-	git_revwalk_listnode *parent;
+	git_rawobj data;
+	int error;
 
-	assert(commit);
+	if (commit->parsed)
+		return GIT_SUCCESS;
 
-	commit->uninteresting = 1;
-	parent = commit->parents.head;
+	if ((error = git_odb_read(&data, walk->repo->db, &commit->oid)) < GIT_SUCCESS)
+		return error;
 
-	while (parent) {
-		mark_uninteresting(parent->walk_commit);
-		parent = parent->next;
+	if (data.type != GIT_OBJ_COMMIT) {
+		git_rawobj_close(&data);
+		return GIT_EOBJTYPE;
 	}
+
+	error = commit_quick_parse(walk, commit, &data);
+	git_rawobj_close(&data);
+	return error;
 }
 
-int git_revwalk_hide(git_revwalk *walk, git_commit *commit)
+static void mark_uninteresting(commit_object *commit)
 {
-	git_revwalk_commit *hide;
+	unsigned short i;
+	assert(commit);
 
-	assert(walk && commit);
-	
-	hide = insert_commit(walk, commit);
-	if (hide == NULL)
-		return GIT_ENOMEM;
+	commit->uninteresting = 1;
 
-	mark_uninteresting(hide);
-	return GIT_SUCCESS;
+	for (i = 0; i < commit->out_degree; ++i)
+		if (!commit->parents[i]->uninteresting)
+			mark_uninteresting(commit->parents[i]);
 }
 
-
-static void prepare_walk(git_revwalk *walk)
+static int process_commit(git_revwalk *walk, commit_object *commit)
 {
-	if (walk->sorting & GIT_SORT_TIME)
-		git_revwalk_list_timesort(&walk->iterator);
-
-	if (walk->sorting & GIT_SORT_TOPOLOGICAL)
-		git_revwalk_list_toposort(&walk->iterator);
+	int error;
 
-	if (walk->sorting & GIT_SORT_REVERSE)
-		walk->next = &git_revwalk_list_pop_back;
-	else
-		walk->next = &git_revwalk_list_pop_front;
+	if (commit->seen)
+		return GIT_SUCCESS;
 
-	walk->walking = 1;
-}
+	commit->seen = 1;
 
-int git_revwalk_next(git_commit **commit, git_revwalk *walk)
-{
-	git_revwalk_commit *next;
+	if ((error = commit_parse(walk, commit)) < GIT_SUCCESS)
+			return error;
 
-	assert(walk && commit);
+	if (commit->uninteresting)
+		mark_uninteresting(commit);
 
-	if (!walk->walking)
-		prepare_walk(walk);
+	return walk->enqueue(walk, commit);
+}
 
-	*commit = NULL;
+static int process_commit_parents(git_revwalk *walk, commit_object *commit)
+{
+	unsigned short i;
+	int error = GIT_SUCCESS;
 
-	while ((next = walk->next(&walk->iterator)) != NULL) {
-		if (!next->uninteresting) {
-			*commit = next->commit_object;
-			GIT_OBJECT_INCREF(walk->repo, *commit);
-			return GIT_SUCCESS;
-		}
+	for (i = 0; i < commit->out_degree && error == GIT_SUCCESS; ++i) {
+		error = process_commit(walk, commit->parents[i]);
 	}
 
-	/* No commits left to iterate */
-	git_revwalk_reset(walk);
-	return GIT_EREVWALKOVER;
+	return error;
 }
 
-void git_revwalk_reset(git_revwalk *walk)
+static int push_commit(git_revwalk *walk, const git_oid *oid, int uninteresting)
 {
-	const void *_unused;
-	git_revwalk_commit *commit;
+	commit_object *commit;
 
-	assert(walk);
+	commit = commit_lookup(walk, oid);
+	if (commit == NULL)
+		return GIT_ENOTFOUND;
 
-	GIT_HASHTABLE_FOREACH(walk->commits, _unused, commit, {
-		GIT_OBJECT_DECREF(walk->repo, commit->commit_object);
-		git_revwalk_list_clear(&commit->parents);
-		free(commit);
-	});
+	if (uninteresting)
+		mark_uninteresting(commit);
 
-	git_hashtable_clear(walk->commits);
-	git_revwalk_list_clear(&walk->iterator);
-	walk->walking = 0;
+	return git_vector_insert(&walk->pending, commit);
 }
 
+int git_revwalk_push(git_revwalk *walk, const git_oid *oid)
+{
+	assert(walk && oid);
+	return push_commit(walk, oid, 0);
+}
 
+int git_revwalk_hide(git_revwalk *walk, const git_oid *oid)
+{
+	assert(walk && oid);
+	return push_commit(walk, oid, 1);
+}
 
-
-
-
-int git_revwalk_list_push_back(git_revwalk_list *list, git_revwalk_commit *commit)
+static int revwalk_enqueue_timesort(git_revwalk *walk, commit_object *commit)
 {
-	git_revwalk_listnode *node = NULL;
+	return git_pqueue_insert(&walk->iterator_time, commit);
+}
 
-	node = git__malloc(sizeof(git_revwalk_listnode));
+static int revwalk_enqueue_unsorted(git_revwalk *walk, commit_object *commit)
+{
+	return commit_list_insert(commit, &walk->iterator_rand) ? GIT_SUCCESS : GIT_ENOMEM;
+}
 
-	if (node == NULL)
-		return GIT_ENOMEM;
+static int revwalk_next_timesort(commit_object **object_out, git_revwalk *walk)
+{
+	int error;
+	commit_object *next;
 
-	node->walk_commit = commit;
-	node->next = NULL;
-	node->prev = list->tail;
+	while ((next = git_pqueue_pop(&walk->iterator_time)) != NULL) {
+		if ((error = process_commit_parents(walk, next)) < GIT_SUCCESS)
+			return error;
 
-	if (list->tail == NULL) {
-		list->head = list->tail = node;
-	} else {
-		list->tail->next = node;
-		list->tail = node;
+		if (!next->uninteresting) {
+			*object_out = next;
+			return GIT_SUCCESS;
+		}
 	}
 
-	list->size++;
-	return 0;
+	return GIT_EREVWALKOVER;
 }
 
-int git_revwalk_list_push_front(git_revwalk_list *list, git_revwalk_commit *commit)
+static int revwalk_next_unsorted(commit_object **object_out, git_revwalk *walk)
 {
-	git_revwalk_listnode *node = NULL;
-
-	node = git__malloc(sizeof(git_revwalk_listnode));
+	int error;
+	commit_object *next;
 
-	if (node == NULL)
-		return GIT_ENOMEM;
+	while ((next = commit_list_pop(&walk->iterator_rand)) != NULL) {
+		if ((error = process_commit_parents(walk, next)) < GIT_SUCCESS)
+			return error;
 
-	node->walk_commit = commit;
-	node->next = list->head;
-	node->prev = NULL;
-
-	if (list->head == NULL) {
-		list->head = list->tail = node;
-	} else {
-		list->head->prev = node;
-		list->head = node;
+		if (!next->uninteresting) {
+			*object_out = next;
+			return GIT_SUCCESS;
+		}
 	}
 
-	list->size++;
-	return 0;
+	return GIT_EREVWALKOVER;
 }
 
-
-git_revwalk_commit *git_revwalk_list_pop_back(git_revwalk_list *list)
+static int revwalk_next_toposort(commit_object **object_out, git_revwalk *walk)
 {
-	git_revwalk_listnode *node;
-	git_revwalk_commit *commit;
+	commit_object *next;
+	unsigned short i;
 
-	if (list->tail == NULL)
-		return NULL;
+	for (;;) {
+		next = commit_list_pop(&walk->iterator_topo);
+		if (next == NULL)
+			return GIT_EREVWALKOVER;
 
-	node = list->tail;
-	list->tail = list->tail->prev;
-	if (list->tail == NULL)
-		list->head = NULL;
-	else
-		list->tail->next = NULL;
+		if (next->in_degree > 0) {
+			next->topo_delay = 1;
+			continue;
+		}
 
-	commit = node->walk_commit;
-	free(node);
+		for (i = 0; i < next->out_degree; ++i) {
+			commit_object *parent = next->parents[i];
 
-	list->size--;
+			if (--parent->in_degree == 0 && parent->topo_delay) {
+				parent->topo_delay = 0;
+				commit_list_insert(parent, &walk->iterator_topo);
+			}
+		}
 
-	return commit;
+		*object_out = next;
+		return GIT_SUCCESS;
+	}
 }
 
-git_revwalk_commit *git_revwalk_list_pop_front(git_revwalk_list *list)
+static int revwalk_next_reverse(commit_object **object_out, git_revwalk *walk)
 {
-	git_revwalk_listnode *node;
-	git_revwalk_commit *commit;
-
-	if (list->head == NULL)
-		return NULL;
-
-	node = list->head;
-	list->head = list->head->next;
-	if (list->head == NULL)
-		list->tail = NULL;
-	else
-		list->head->prev = NULL;
+	*object_out = commit_list_pop(&walk->iterator_reverse);
+	return *object_out ? GIT_SUCCESS : GIT_EREVWALKOVER;
+}
 
-	commit = node->walk_commit;
-	free(node);
 
-	list->size--;
+static int prepare_walk(git_revwalk *walk)
+{
+	unsigned int i;
+	int error;
 
-	return commit;
-}
+	if (walk->sorting & GIT_SORT_TIME) {
+		if ((error = git_pqueue_init(&walk->iterator_time, 32, commit_time_cmp)) < GIT_SUCCESS)
+			return error;
 
-void git_revwalk_list_clear(git_revwalk_list *list)
-{
-	git_revwalk_listnode *node, *next_node;
+		walk->get_next = &revwalk_next_timesort;
+		walk->enqueue = &revwalk_enqueue_timesort;
+	} else {
+		walk->get_next = &revwalk_next_unsorted;
+		walk->enqueue = &revwalk_enqueue_unsorted;
+	}
 
-	node = list->head;
-	while (node) {
-		next_node = node->next;
-		free(node);
-		node = next_node;
+	for (i = 0; i < walk->pending.length; ++i) {
+		commit_object *commit = walk->pending.contents[i];
+		if ((error = process_commit(walk, commit)) < GIT_SUCCESS) {
+			return error;
+		}
 	}
 
-	list->head = list->tail = NULL;
-	list->size = 0;
-}
+	if (walk->sorting & GIT_SORT_TOPOLOGICAL) {
+		commit_object *next;
+		unsigned short i;
+		int error;
 
-void git_revwalk_list_timesort(git_revwalk_list *list)
-{
-	git_revwalk_listnode *p, *q, *e;
-	int in_size, p_size, q_size, merge_count, i;
+		while ((error = walk->get_next(&next, walk)) == GIT_SUCCESS) {
+			for (i = 0; i < next->out_degree; ++i) {
+				commit_object *parent = next->parents[i];
+				parent->in_degree++;
+			}
 
-	if (list->head == NULL)
-		return;
+			commit_list_insert(next, &walk->iterator_topo);
+		}
 
-	in_size = 1;
+		if (error != GIT_EREVWALKOVER)
+			return error;
 
-	do {
-		p = list->head;
-		list->tail = NULL;
-		merge_count = 0;
+		walk->get_next = &revwalk_next_toposort;
+	}
 
-		while (p != NULL) {
-			merge_count++;
-			q = p;
-			p_size = 0;
-			q_size = in_size;
+	if (walk->sorting & GIT_SORT_REVERSE) {
+		commit_object *next;
+		int error;
 
-			for (i = 0; i < in_size && q; ++i, q = q->next)
-				p_size++;
+		while ((error = walk->get_next(&next, walk)) == GIT_SUCCESS)
+			commit_list_insert(next, &walk->iterator_reverse);
 
-			while (p_size > 0 || (q_size > 0 && q)) {
+		if (error != GIT_EREVWALKOVER)
+			return error;
 
-				if (p_size == 0)
-					e = q, q = q->next, q_size--;
+		walk->get_next = &revwalk_next_reverse;
+	}
 
-				else if (q_size == 0 || q == NULL ||
-						p->walk_commit->commit_object->committer->when.time >= 
-						q->walk_commit->commit_object->committer->when.time)
-					e = p, p = p->next, p_size--;
+	walk->walking = 1;
+	return GIT_SUCCESS;
+}
 
-				else
-					e = q, q = q->next, q_size--;
 
-				if (list->tail != NULL)
-					list->tail->next = e;
-				else
-					list->head = e;
+int git_revwalk_next(git_oid *oid, git_revwalk *walk)
+{
+	int error;
+	commit_object *next;
 
-				e->prev = list->tail;
-				list->tail = e;
-			}
+	assert(walk && oid);
 
-			p = q;
-		}
+	if (!walk->walking) {
+		if ((error = prepare_walk(walk)) < GIT_SUCCESS)
+			return error;
+	}
 
-		list->tail->next = NULL;
-		in_size *= 2;
+	error = walk->get_next(&next, walk);
+	if (error < GIT_SUCCESS)
+		return error;
 
-	} while (merge_count > 1);
+	git_oid_cpy(oid, &next->oid);
+	return GIT_SUCCESS;
 }
 
-void git_revwalk_list_toposort(git_revwalk_list *list)
+void git_revwalk_reset(git_revwalk *walk)
 {
-	git_revwalk_commit *commit;
-	git_revwalk_list topo;
-	memset(&topo, 0x0, sizeof(git_revwalk_list));
-
-	while ((commit = git_revwalk_list_pop_back(list)) != NULL) {
-		git_revwalk_listnode *p;
-
-		if (commit->in_degree > 0) {
-			commit->topo_delay = 1;
-			continue;
-		}
-
-		for (p = commit->parents.head; p != NULL; p = p->next) {
-			p->walk_commit->in_degree--;
+	const void *_unused;
+	commit_object *commit;
 
-			if (p->walk_commit->in_degree == 0 && p->walk_commit->topo_delay) {
-				p->walk_commit->topo_delay = 0;
-				git_revwalk_list_push_back(list, p->walk_commit);
-			}
-		}
+	assert(walk);
 
-		git_revwalk_list_push_back(&topo, commit);
-	}
+	GIT_HASHTABLE_FOREACH(walk->commits, _unused, commit,
+		commit->seen = 0;
+		commit->in_degree = 0;
+		commit->topo_delay = 0;
+	);
 
-	list->head = topo.head;
-	list->tail = topo.tail;
-	list->size = topo.size;
+	git_pqueue_free(&walk->iterator_time);
+	commit_list_free(walk->iterator_topo);
+	commit_list_free(walk->iterator_rand);
+	commit_list_free(walk->iterator_reverse);
+	walk->walking = 0;
 }