util/hash_table: add _mesa_hash_table_clear (v4)

v4: coding style change (Matt Turner)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> (v3)

src/util/hash_table.c

@@ -163,6 +163,32 @@ _mesa_hash_table_destroy(struct hash_table *ht,
    ralloc_free(ht);
 }
 
+/**
+ * Deletes all entries of the given hash table without deleting the table
+ * itself or changing its structure.
+ *
+ * If delete_function is passed, it gets called on each entry present.
+ */
+void
+_mesa_hash_table_clear(struct hash_table *ht,
+                       void (*delete_function)(struct hash_entry *entry))
+{
+   struct hash_entry *entry;
+
+   for (entry = ht->table; entry != ht->table + ht->size; entry++) {
+      if (entry->key == NULL)
+         continue;
+
+      if (delete_function != NULL && entry->key != ht->deleted_key)
+         delete_function(entry);
+
+      entry->key = NULL;
+   }
+
+   ht->entries = 0;
+   ht->deleted_entries = 0;
+}
+
 /** Sets the value of the key pointer used for deleted entries in the table.
  *
  * The assumption is that usually keys are actual pointers, so we use a