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, 2 insertions, 0 deletions

diff --git a/src/shared/set.h b/src/shared/set.h
index f1111d1bc8..ae3090a09f 100644
--- a/src/shared/set.h
+++ b/src/shared/set.h
@@ -37,6 +37,8 @@ int set_put(Set *s, void *value);
 void *set_get(Set *s, void *value);
 bool set_contains(Set *s, void *value);
 
+int set_reserve(Set *s, unsigned entries_add);
+
 void *set_iterate(Set *s, Iterator *i);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(Set*, set_free);