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index-pack: eliminate unlimited recursion in get_base_data()

Revese the order of delta applying so that by the time a delta is
applied, its base is either non-delta or already inflated.
get_base_data() is still recursive, but because base's data is always
ready, the inner get_base_data() call never has any chance to call
itself again.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 parent 2baad22 commit 20e95d0a8475ce467903e1aaad5c2fd47777fcc8 @pclouds pclouds committed with gitster Jan 14, 2012
Showing with 44 additions and 9 deletions.
  1. +44 −9 builtin/index-pack.c
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@@ -515,28 +515,63 @@ static int is_delta_type(enum object_type type)
return (type == OBJ_REF_DELTA || type == OBJ_OFS_DELTA);
}
+/*
+ * This function is part of find_unresolved_deltas(). There are two
+ * walkers going in the opposite ways.
+ *
+ * The first one in find_unresolved_deltas() traverses down from
+ * parent node to children, deflating nodes along the way. However,
+ * memory for deflated nodes is limited by delta_base_cache_limit, so
+ * at some point parent node's deflated content may be freed.
+ *
+ * The second walker is this function, which goes from current node up
+ * to top parent if necessary to deflate the node. In normal
+ * situation, its parent node would be already deflated, so it just
+ * needs to apply delta.
+ *
+ * In the worst case scenario, parent node is no longer deflated because
+ * we're running out of delta_base_cache_limit; we need to re-deflate
+ * parents, possibly up to the top base.
+ *
+ * All deflated objects here are subject to be freed if we exceed
+ * delta_base_cache_limit, just like in find_unresolved_deltas(), we
+ * just need to make sure the last node is not freed.
+ */
static void *get_base_data(struct base_data *c)
{
if (!c->data) {
struct object_entry *obj = c->obj;
+ struct base_data **delta = NULL;
+ int delta_nr = 0, delta_alloc = 0;
- if (is_delta_type(obj->type)) {
- void *base = get_base_data(c->base);
- void *raw = get_data_from_pack(obj);
+ while (is_delta_type(c->obj->type) && !c->data) {
+ ALLOC_GROW(delta, delta_nr + 1, delta_alloc);
+ delta[delta_nr++] = c;
+ c = c->base;
+ }
+ if (!delta_nr) {
+ c->data = get_data_from_pack(obj);
+ c->size = obj->size;
+ base_cache_used += c->size;
+ prune_base_data(c);
+ }
+ for (; delta_nr > 0; delta_nr--) {
+ void *base, *raw;
+ c = delta[delta_nr - 1];
+ obj = c->obj;
+ base = get_base_data(c->base);
+ raw = get_data_from_pack(obj);
c->data = patch_delta(
base, c->base->size,
raw, obj->size,
&c->size);
free(raw);
if (!c->data)
bad_object(obj->idx.offset, "failed to apply delta");
- } else {
- c->data = get_data_from_pack(obj);
- c->size = obj->size;
+ base_cache_used += c->size;
+ prune_base_data(c);
}
-
- base_cache_used += c->size;
- prune_base_data(c);
+ free(delta);
}
return c->data;
}

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