split-index: add and use unshare_split_index()

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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/read-cache.c b/read-cache.c
index 0d0081a11b858227d3f55ebbc21f04bd49875f68..8da84ae2d19c93220c6fb7e2956508396ab65c7a 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -1877,15 +1877,9 @@ int discard_index(struct index_state *istate)
 {
        int i;
 
 {
        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]);
                free(istate->cache[i]);

-       }

        resolve_undo_clear_index(istate);
        istate->cache_nr = 0;
        istate->cache_changed = 0;
        resolve_undo_clear_index(istate);
        istate->cache_nr = 0;
        istate->cache_changed = 0;

diff --git a/split-index.c b/split-index.c
index f519e60f87578386ec9b4ea764bf530be0f64836..49bd197f715ae783d7fdbe8e1d638a1bcac0073c 100644 (file)
--- a/split-index.c
+++ b/split-index.c
@@ -73,10 +73,17 @@ void move_cache_to_base_index(struct index_state *istate)
        int i;
 
        /*
        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() */
        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;
 }
 
        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;
 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)
        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)
 {
 
 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 df91c1bda8117fe7d0f25a0aaedce79370801ce0..65c0f09b2bd413e091cc65ef2f0d3a2d92aeb858 100644 (file)
--- 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 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
 
 #endif