[PATCH 1/2] split-index: add and use unshare_split_index()
From: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
When split-index is being used, we have two cache_entry arrays in index_state->cache[] and index_state->split_index->base->cache[].
index_state->cache[] may share the same entries with base->cache[] so we can quickly determine what entries are shared. This makes memory management tricky, we can't free base->cache[] until we know index_state->cache[] does not point to any of those entries.
unshare_split_index() is added for this purpose, to find shared entries and either duplicate them in index_state->cache[], or discard them. Either way it should be safe to free base->cache[] after unshare_split_index().
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
read-cache.c | 10 ++--------
split-index.c | 57 ++++++++++++++++++++++++++++++++++++++++++++-------------
split-index.h | 1 +
3 files changed, 47 insertions(+), 21 deletions(-)
Show changes to 3 files +47 −21
read-cache.c, split-index.c, split-index.h
diff --git a/read-cache.c b/read-cache.c
index 0d0081a11b..8da84ae2d1 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1877,15 +1877,9 @@ int discard_index(struct index_state *istate)
{
int i;
- for (i = 0; i < istate->cache_nr; i++) {
- if (istate->cache[i]->index &&
- istate->split_index &&
- istate->split_index->base &&
- istate->cache[i]->index <= istate->split_index->base->cache_nr &&
- istate->cache[i] == istate->split_index->base->cache[istate->cache[i]->index - 1])
- continue;
+ unshare_split_index(istate, 1);
+ for (i = 0; i < istate->cache_nr; i++)
free(istate->cache[i]);
- }
resolve_undo_clear_index(istate);
istate->cache_nr = 0;
istate->cache_changed = 0;
diff --git a/split-index.c b/split-index.c
index f519e60f87..49bd197f71 100644
--- a/split-index.c
+++ b/split-index.c
@@ -73,10 +73,17 @@ void move_cache_to_base_index(struct index_state *istate)
int i;
/*
- * do not delete old si->base, its index entries may be shared
- * with istate->cache[]. Accept a bit of leaking here because
- * this code is only used by short-lived update-index.
+ * If "si" is shared with another index_state (e.g. by
+ * unpack-trees code), we will need to duplicate split_index
+ * struct. It's not happening now though, luckily.
*/
+ assert(si->refcount <= 1);
+
+ unshare_split_index(istate, 0);
+ if (si->base) {
+ discard_index(si->base);
+ free(si->base);
+ }
si->base = xcalloc(1, sizeof(*si->base));
si->base->version = istate->version;
/* zero timestamp disables racy test in ce_write_index() */
@@ -275,11 +282,41 @@ void finish_writing_split_index(struct index_state *istate)
istate->cache_nr = si->saved_cache_nr;
}
+void unshare_split_index(struct index_state *istate, int discard)
+{
+ struct split_index *si = istate->split_index;
+ int i;
+
+ if (!si || !si->base)
+ return;
+
+ for (i = 0; i < istate->cache_nr; i++) {
+ struct cache_entry *ce = istate->cache[i];
+ struct cache_entry *new = NULL;
+
+ if (!ce->index ||
+ ce->index > si->base->cache_nr ||
+ ce != si->base->cache[ce->index - 1])
+ continue;
+
+ if (!discard) {
+ int len = ce_namelen(ce);
+ new = xcalloc(1, cache_entry_size(len));
+ copy_cache_entry(new, ce);
+ memcpy(new->name, ce->name, len);
+ new->index = 0;
+ }
+ istate->cache[i] = new;
+ }
+}
+
+
void discard_split_index(struct index_state *istate)
{
struct split_index *si = istate->split_index;
if (!si)
return;
+ unshare_split_index(istate, 0);
istate->split_index = NULL;
si->refcount--;
if (si->refcount)
@@ -328,14 +365,8 @@ void add_split_index(struct index_state *istate)
void remove_split_index(struct index_state *istate)
{
- if (istate->split_index) {
- /*
- * can't discard_split_index(&the_index); because that
- * will destroy split_index->base->cache[], which may
- * be shared with the_index.cache[]. So yeah we're
- * leaking a bit here.
- */
- istate->split_index = NULL;
- istate->cache_changed |= SOMETHING_CHANGED;
- }
+ if (!istate->split_index)
+ return;
+ discard_split_index(istate);
+ istate->cache_changed |= SOMETHING_CHANGED;
}
diff --git a/split-index.h b/split-index.h
index df91c1bda8..65c0f09b2b 100644
--- a/split-index.h
+++ b/split-index.h
@@ -33,5 +33,6 @@ void finish_writing_split_index(struct index_state *istate);
void discard_split_index(struct index_state *istate);
void add_split_index(struct index_state *istate);
void remove_split_index(struct index_state *istate);
+void unshare_split_index(struct index_state *istate, int discard);
#endif
--
2.13.0.rc1.83.g83955d3ecd.dirty
Christian Couder