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index-pack: eliminate recursion in find_unresolved_deltas

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Current find_unresolved_deltas() links all bases together in a form of
tree, using struct base_data, with prev_base pointer to point to
parent node. Then it traverses down from parent to children in
recursive manner with all base_data allocated on stack.

To eliminate recursion, we simply need to put all on heap
(parse_pack_objects and fix_unresolved_deltas). After that, it's
simple non-recursive depth-first traversal loop. Each node also
maintains its own state (ofs and ref indices) to iterate over all
children nodes.

So we process one node:

 - if it returns a new (child) node (a parent base), we link it to our
   tree, then process the new node.

 - if it returns nothing, the node is done, free it. We go back to
   parent node and resume whatever it's doing.

and do it until we have no nodes to process.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy 2012-01-14 19:19:54 +07:00 committed by Junio C Hamano
parent 941ba8db57
commit 2baad22013
1 changed files with 71 additions and 42 deletions
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113
builtin/index-pack.c
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@ -34,6 +34,8 @@ struct base_data {
struct object_entry *obj;
void *data;
unsigned long size;
int ref_first, ref_last;
int ofs_first, ofs_last;
};
/*
@ -221,6 +223,15 @@ static NORETURN void bad_object(unsigned long offset, const char *format, ...)
die("pack has bad object at offset %lu: %s", offset, buf);
}
static struct base_data *alloc_base_data(void)
{
struct base_data *base = xmalloc(sizeof(struct base_data));
memset(base, 0, sizeof(*base));
base->ref_last = -1;
base->ofs_last = -1;
return base;
}
static void free_base_data(struct base_data *c)
{
if (c->data) {
@ -553,58 +564,76 @@ static void resolve_delta(struct object_entry *delta_obj,
nr_resolved_deltas++;
}
static void find_unresolved_deltas(struct base_data *base,
struct base_data *prev_base)
static struct base_data *find_unresolved_deltas_1(struct base_data *base,
struct base_data *prev_base)
{
int i, ref_first, ref_last, ofs_first, ofs_last;
/*
* This is a recursive function. Those brackets should help reducing
* stack usage by limiting the scope of the delta_base union.
*/
{
if (base->ref_last == -1 && base->ofs_last == -1) {
union delta_base base_spec;
hashcpy(base_spec.sha1, base->obj->idx.sha1);
find_delta_children(&base_spec,
&ref_first, &ref_last, OBJ_REF_DELTA);
&base->ref_first, &base->ref_last, OBJ_REF_DELTA);
memset(&base_spec, 0, sizeof(base_spec));
base_spec.offset = base->obj->idx.offset;
find_delta_children(&base_spec,
&ofs_first, &ofs_last, OBJ_OFS_DELTA);
&base->ofs_first, &base->ofs_last, OBJ_OFS_DELTA);
if (base->ref_last == -1 && base->ofs_last == -1) {
free(base->data);
return NULL;
}
link_base_data(prev_base, base);
}
if (ref_last == -1 && ofs_last == -1) {
free(base->data);
return;
}
link_base_data(prev_base, base);
for (i = ref_first; i <= ref_last; i++) {
struct object_entry *child = objects + deltas[i].obj_no;
struct base_data result;
if (base->ref_first <= base->ref_last) {
struct object_entry *child = objects + deltas[base->ref_first].obj_no;
struct base_data *result = alloc_base_data();
assert(child->real_type == OBJ_REF_DELTA);
resolve_delta(child, base, &result);
if (i == ref_last && ofs_last == -1)
resolve_delta(child, base, result);
if (base->ref_first == base->ref_last && base->ofs_last == -1)
free_base_data(base);
find_unresolved_deltas(&result, base);
base->ref_first++;
return result;
}
for (i = ofs_first; i <= ofs_last; i++) {
struct object_entry *child = objects + deltas[i].obj_no;
struct base_data result;
if (base->ofs_first <= base->ofs_last) {
struct object_entry *child = objects + deltas[base->ofs_first].obj_no;
struct base_data *result = alloc_base_data();
assert(child->real_type == OBJ_OFS_DELTA);
resolve_delta(child, base, &result);
if (i == ofs_last)
resolve_delta(child, base, result);
if (base->ofs_first == base->ofs_last)
free_base_data(base);
find_unresolved_deltas(&result, base);
base->ofs_first++;
return result;
}
unlink_base_data(base);
return NULL;
}
static void find_unresolved_deltas(struct base_data *base)
{
struct base_data *new_base, *prev_base = NULL;
for (;;) {
new_base = find_unresolved_deltas_1(base, prev_base);
if (new_base) {
prev_base = base;
base = new_base;
} else {
free(base);
base = prev_base;
if (!base)
return;
prev_base = base->base;
}
}
}
static int compare_delta_entry(const void *a, const void *b)
@ -684,13 +713,13 @@ static void parse_pack_objects(unsigned char *sha1)
progress = start_progress("Resolving deltas", nr_deltas);
for (i = 0; i < nr_objects; i++) {
struct object_entry *obj = &objects[i];
struct base_data base_obj;
struct base_data *base_obj = alloc_base_data();
if (is_delta_type(obj->type))
continue;
base_obj.obj = obj;
base_obj.data = NULL;
find_unresolved_deltas(&base_obj, NULL);
base_obj->obj = obj;
base_obj->data = NULL;
find_unresolved_deltas(base_obj);
display_progress(progress, nr_resolved_deltas);
}
}
@ -783,20 +812,20 @@ static void fix_unresolved_deltas(struct sha1file *f, int nr_unresolved)
for (i = 0; i < n; i++) {
struct delta_entry *d = sorted_by_pos[i];
enum object_type type;
struct base_data base_obj;
struct base_data *base_obj = alloc_base_data();
if (objects[d->obj_no].real_type != OBJ_REF_DELTA)
continue;
base_obj.data = read_sha1_file(d->base.sha1, &type, &base_obj.size);
if (!base_obj.data)
base_obj->data = read_sha1_file(d->base.sha1, &type, &base_obj->size);
if (!base_obj->data)
continue;
if (check_sha1_signature(d->base.sha1, base_obj.data,
base_obj.size, typename(type)))
if (check_sha1_signature(d->base.sha1, base_obj->data,
base_obj->size, typename(type)))
die("local object %s is corrupt", sha1_to_hex(d->base.sha1));
base_obj.obj = append_obj_to_pack(f, d->base.sha1,
base_obj.data, base_obj.size, type);
find_unresolved_deltas(&base_obj, NULL);
base_obj->obj = append_obj_to_pack(f, d->base.sha1,
base_obj->data, base_obj->size, type);
find_unresolved_deltas(base_obj);
display_progress(progress, nr_resolved_deltas);
}
free(sorted_by_pos);