fetch: replace string-list used as a look-up table with a hashmap

In find_non_local_tags() helper function (used to implement the
"follow tags"), we use string_list_has_string() on two string lists
as a way to see if a refname has already been processed, etc.

All this code predates more modern in-core lookup API like hashmap;
replace them with two hashmaps and one string list---the hashmaps
are used for look-ups and the string list is to keep the order of
items in the returned result stable (which is the only single thing
hashmap does worse than lookups on string-list).

Similarly, get_ref_map() uses another string-list as a look-up table
for existing refs.  Replace it with a hashmap.

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

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 0696abfc2a158baa3177fa9e71e2c16bc64655a4..aee1d9bf21cf7786ab4dad6590f914242a870a37 100644 (file)
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -223,18 +223,6 @@ static void add_merge_config(struct ref **head,
        }
 }
 
-static int add_existing(const char *refname, const struct object_id *oid,
-                       int flag, void *cbdata)
-{
-       struct string_list *list = (struct string_list *)cbdata;
-       struct string_list_item *item = string_list_insert(list, refname);
-       struct object_id *old_oid = xmalloc(sizeof(*old_oid));
-
-       oidcpy(old_oid, oid);
-       item->util = old_oid;
-       return 0;
-}
-
 static int will_fetch(struct ref **head, const unsigned char *sha1)
 {
        struct ref *rm = *head;
@@ -246,16 +234,72 @@ static int will_fetch(struct ref **head, const unsigned char *sha1)
        return 0;
 }
 
+struct refname_hash_entry {
+       struct hashmap_entry ent; /* must be the first member */
+       struct object_id oid;
+       char refname[FLEX_ARRAY];
+};
+
+static int refname_hash_entry_cmp(const void *hashmap_cmp_fn_data,
+                                 const void *e1_,
+                                 const void *e2_,
+                                 const void *keydata)
+{
+       const struct refname_hash_entry *e1 = e1_;
+       const struct refname_hash_entry *e2 = e2_;
+
+       return strcmp(e1->refname, keydata ? keydata : e2->refname);
+}
+
+static struct refname_hash_entry *refname_hash_add(struct hashmap *map,
+                                                  const char *refname,
+                                                  const struct object_id *oid)
+{
+       struct refname_hash_entry *ent;
+       size_t len = strlen(refname);
+
+       FLEX_ALLOC_MEM(ent, refname, refname, len);
+       hashmap_entry_init(ent, strhash(refname));
+       oidcpy(&ent->oid, oid);
+       hashmap_add(map, ent);
+       return ent;
+}
+
+static int add_one_refname(const char *refname,
+                          const struct object_id *oid,
+                          int flag, void *cbdata)
+{
+       struct hashmap *refname_map = cbdata;
+
+       (void) refname_hash_add(refname_map, refname, oid);
+       return 0;
+}
+
+static void refname_hash_init(struct hashmap *map)
+{
+       hashmap_init(map, refname_hash_entry_cmp, NULL, 0);
+}
+
+static int refname_hash_exists(struct hashmap *map, const char *refname)
+{
+       return !!hashmap_get_from_hash(map, strhash(refname), refname);
+}
+
 static void find_non_local_tags(const struct ref *refs,
                                struct ref **head,
                                struct ref ***tail)
 {
-       struct string_list existing_refs = STRING_LIST_INIT_DUP;
-       struct string_list remote_refs = STRING_LIST_INIT_NODUP;
+       struct hashmap existing_refs;
+       struct hashmap remote_refs;
+       struct string_list remote_refs_list = STRING_LIST_INIT_NODUP;
+       struct string_list_item *remote_ref_item;
        const struct ref *ref;
-       struct string_list_item *item = NULL;
+       struct refname_hash_entry *item = NULL;
+
+       refname_hash_init(&existing_refs);
+       refname_hash_init(&remote_refs);
 
-       for_each_ref(add_existing, &existing_refs);
+       for_each_ref(add_one_refname, &existing_refs);
        for (ref = refs; ref; ref = ref->next) {
                if (!starts_with(ref->name, "refs/tags/"))
                        continue;
@@ -271,10 +315,10 @@ static void find_non_local_tags(const struct ref *refs,
                            !has_object_file_with_flags(&ref->old_oid,
                                                        OBJECT_INFO_QUICK) &&
                            !will_fetch(head, ref->old_oid.hash) &&
-                           !has_sha1_file_with_flags(item->util,
+                           !has_sha1_file_with_flags(item->oid.hash,
                                                      OBJECT_INFO_QUICK) &&
-                           !will_fetch(head, item->util))
-                               item->util = NULL;
+                           !will_fetch(head, item->oid.hash))
+                               oidclr(&item->oid);
                        item = NULL;
                        continue;
                }
@@ -286,48 +330,53 @@ static void find_non_local_tags(const struct ref *refs,
                 * fetch.
                 */
                if (item &&
-                   !has_sha1_file_with_flags(item->util, OBJECT_INFO_QUICK) &&
-                   !will_fetch(head, item->util))
-                       item->util = NULL;
+                   !has_sha1_file_with_flags(item->oid.hash, OBJECT_INFO_QUICK) &&
+                   !will_fetch(head, item->oid.hash))
+                       oidclr(&item->oid);
 
                item = NULL;
 
                /* skip duplicates and refs that we already have */
-               if (string_list_has_string(&remote_refs, ref->name) ||
-                   string_list_has_string(&existing_refs, ref->name))
+               if (refname_hash_exists(&remote_refs, ref->name) ||
+                   refname_hash_exists(&existing_refs, ref->name))
                        continue;
 
-               item = string_list_insert(&remote_refs, ref->name);
-               item->util = (void *)&ref->old_oid;
+               item = refname_hash_add(&remote_refs, ref->name, &ref->old_oid);
+               string_list_insert(&remote_refs_list, ref->name);
        }
-       string_list_clear(&existing_refs, 1);
+       hashmap_free(&existing_refs, 1);
 
        /*
         * We may have a final lightweight tag that needs to be
         * checked to see if it needs fetching.
         */
        if (item &&
-           !has_sha1_file_with_flags(item->util, OBJECT_INFO_QUICK) &&
-           !will_fetch(head, item->util))
-               item->util = NULL;
+           !has_sha1_file_with_flags(item->oid.hash, OBJECT_INFO_QUICK) &&
+           !will_fetch(head, item->oid.hash))
+               oidclr(&item->oid);
 
        /*
-        * For all the tags in the remote_refs string list,
+        * For all the tags in the remote_refs_list,
         * add them to the list of refs to be fetched
         */
-       for_each_string_list_item(item, &remote_refs) {
+       for_each_string_list_item(remote_ref_item, &remote_refs_list) {
+               const char *refname = remote_ref_item->string;
+
+               item = hashmap_get_from_hash(&remote_refs, strhash(refname), refname);
+               if (!item)
+                       BUG("unseen remote ref?");
+
                /* Unless we have already decided to ignore this item... */
-               if (item->util)
-               {
-                       struct ref *rm = alloc_ref(item->string);
-                       rm->peer_ref = alloc_ref(item->string);
-                       oidcpy(&rm->old_oid, item->util);
+               if (!is_null_oid(&item->oid)) {
+                       struct ref *rm = alloc_ref(item->refname);
+                       rm->peer_ref = alloc_ref(item->refname);
+                       oidcpy(&rm->old_oid, &item->oid);
                        **tail = rm;
                        *tail = &rm->next;
                }
        }
-
-       string_list_clear(&remote_refs, 0);
+       hashmap_free(&remote_refs, 1);
+       string_list_clear(&remote_refs_list, 0);
 }
 
 static struct ref *get_ref_map(struct remote *remote,
@@ -343,7 +392,7 @@ static struct ref *get_ref_map(struct remote *remote,
        /* opportunistically-updated references: */
        struct ref *orefs = NULL, **oref_tail = &orefs;
 
-       struct string_list existing_refs = STRING_LIST_INIT_DUP;
+       struct hashmap existing_refs;
 
        if (rs->nr) {
                struct refspec *fetch_refspec;
@@ -437,19 +486,24 @@ static struct ref *get_ref_map(struct remote *remote,
 
        ref_map = ref_remove_duplicates(ref_map);
 
-       for_each_ref(add_existing, &existing_refs);
+       refname_hash_init(&existing_refs);
+       for_each_ref(add_one_refname, &existing_refs);
+
        for (rm = ref_map; rm; rm = rm->next) {
                if (rm->peer_ref) {
-                       struct string_list_item *peer_item =
-                               string_list_lookup(&existing_refs,
-                                                  rm->peer_ref->name);
+                       const char *refname = rm->peer_ref->name;
+                       struct refname_hash_entry *peer_item;
+
+                       peer_item = hashmap_get_from_hash(&existing_refs,
+                                                         strhash(refname),
+                                                         refname);
                        if (peer_item) {
-                               struct object_id *old_oid = peer_item->util;
+                               struct object_id *old_oid = &peer_item->oid;
                                oidcpy(&rm->peer_ref->old_oid, old_oid);
                        }
                }
        }
-       string_list_clear(&existing_refs, 1);
+       hashmap_free(&existing_refs, 1);
 
        return ref_map;
 }