hashmap: add disallow_rehash setting

Teach hashmap to allow rehashes to be suppressed.
This is useful when hashmaps are accessed by multiple
threads.  It still requires the caller to properly
manage their locking.  This just prevents unexpected
rehashing during inserts and deletes.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/hashmap.c b/hashmap.c
index 93793cb954..7d1044eb5d 100644
--- a/hashmap.c
+++ b/hashmap.c
@@ -104,11 +104,19 @@ static inline unsigned int bucket(const struct hashmap *map,
 	return key->hash & (map->tablesize - 1);
 }
 
+int hashmap_bucket(const struct hashmap *map, unsigned int hash)
+{
+	return hash & (map->tablesize - 1);
+}
+
 static void rehash(struct hashmap *map, unsigned int newsize)
 {
 	unsigned int i, oldsize = map->tablesize;
 	struct hashmap_entry **oldtable = map->table;
 
+	if (map->disallow_rehash)
+		return;
+
 	alloc_table(map, newsize);
 	for (i = 0; i < oldsize; i++) {
 		struct hashmap_entry *e = oldtable[i];
@@ -141,7 +149,9 @@ void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
 		size_t initial_size)
 {
 	unsigned int size = HASHMAP_INITIAL_SIZE;
-	map->size = 0;
+
+	memset(map, 0, sizeof(*map));
+
 	map->cmpfn = equals_function ? equals_function : always_equal;
 
 	/* calculate initial table size and allocate the table */