hashmap: introduce hashmap_reserve()

With the current hashmap implementation that uses chaining, placing a
reservation can serve two purposes:
 - To optimize putting of entries if the number of entries to put is
   known. The reservation allocates buckets, so later resizing can be
   avoided.
 - To avoid having very long bucket chains after using
   hashmap_move(_one).

In an alternative hashmap implementation it will serve an additional
purpose:
 - To guarantee a subsequent hashmap_move(_one) will not fail with
   -ENOMEM (this never happens in the current implementation).

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/shared/hashmap.h b/src/shared/hashmap.h
index 53b04eb033..22bda37437 100644
--- a/src/shared/hashmap.h
+++ b/src/shared/hashmap.h
@@ -65,6 +65,7 @@ int hashmap_put(Hashmap *h, const void *key, void *value);
 void *hashmap_get(Hashmap *h, const void *key);
 void *hashmap_get2(Hashmap *h, const void *key, void **rkey);
 bool hashmap_contains(Hashmap *h, const void *key);
+int hashmap_reserve(Hashmap *h, unsigned entries_add);
 
 unsigned hashmap_size(Hashmap *h) _pure_;