[PATCH 3/6] hashmap: Add disallow_rehash setting

From

Ggit@jeffhostetler.com <git@jeffhostetler.com>

Date

Mar 22, 2017, 17:14 UTC

Message-ID

<1490202865-31325-4-git-send-email-git@jeffhostetler.com>

In-Reply-To

<1490202865-31325-1-git-send-email-git@jeffhostetler.com>

From: Jeff Hostetler <jeffhost@microsoft.com>

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 hashmap.c | 12 +++++++++++-
 hashmap.h | 24 ++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/hashmap.c b/hashmap.c
index 505e63f..37dfc37 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 */
diff --git a/hashmap.h b/hashmap.h
index 45eda69..de6022a 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -39,6 +39,7 @@ struct hashmap {
 	struct hashmap_entry **table;
 	hashmap_cmp_fn cmpfn;
 	unsigned int size, tablesize, grow_at, shrink_at;
+	unsigned disallow_rehash : 1;
 };
 
 struct hashmap_iter {
@@ -77,6 +78,29 @@ static inline void *hashmap_get_from_hash(const struct hashmap *map,
 	return hashmap_get(map, &key, keydata);
 }
 
+int hashmap_bucket(const struct hashmap *map, unsigned int hash);
+
+/*
+ * Disallow/allow rehashing of the hashmap.
+ * This is useful if the caller knows that the hashmap
+ * needs multi-threaded access.  The caller is still
+ * required to guard/lock searches and inserts in a
+ * manner appropriate to their usage.  This simply
+ * prevents the table from being unexpectedly re-mapped.
+ *
+ * If is up to the caller to ensure that the hashmap is
+ * initialized to a reasonable size to prevent poor
+ * performance.
+ *
+ * When value=1, prevent future rehashes on adds and deleted.
+ * When value=0, allow future rehahses.  This DOES NOT force
+ * a rehash now.
+ */
+static inline void hashmap_disallow_rehash(struct hashmap *map, unsigned value)
+{
+	map->disallow_rehash = value;
+}
+
 /* hashmap_iter functions */
 
 extern void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter);

-- 
2.7.4