From 4531818f12221fdedba9f6f4913d22228628328c Mon Sep 17 00:00:00 2001 From: Michal Schmidt Date: Sat, 25 Oct 2014 18:18:26 -0400 Subject: 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 --- src/shared/hashmap.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) (limited to 'src/shared/hashmap.c') diff --git a/src/shared/hashmap.c b/src/shared/hashmap.c index e965167258..fa4edf11c6 100644 --- a/src/shared/hashmap.c +++ b/src/shared/hashmap.c @@ -276,18 +276,26 @@ static struct hashmap_entry *hash_scan(Hashmap *h, unsigned hash, const void *ke return NULL; } -static int resize_buckets(Hashmap *h) { +static int resize_buckets(Hashmap *h, unsigned entries_add) { struct hashmap_entry **n, *i; - unsigned m; + unsigned m, new_n_entries, new_n_buckets; uint8_t nkey[HASH_KEY_SIZE]; assert(h); - if (_likely_(h->n_entries*4 < h->n_buckets*3)) + new_n_entries = h->n_entries + entries_add; + + /* overflow? */ + if (_unlikely_(new_n_entries < entries_add || new_n_entries > UINT_MAX / 4)) + return -ENOMEM; + + new_n_buckets = new_n_entries * 4 / 3; + + if (_likely_(new_n_buckets <= h->n_buckets)) return 0; - /* Increase by four */ - m = (h->n_entries+1)*4-1; + /* Increase by four at least */ + m = MAX((h->n_entries+1)*4-1, new_n_buckets); /* If we hit OOM we simply risk packed hashmaps... */ n = new0(struct hashmap_entry*, m); @@ -339,7 +347,7 @@ static int __hashmap_put(Hashmap *h, const void *key, void *value, unsigned hash struct hashmap_entry *e; - if (resize_buckets(h) > 0) + if (resize_buckets(h, 1) > 0) hash = bucket_hash(h, key); if (h->from_pool) @@ -476,6 +484,18 @@ unsigned hashmap_size(Hashmap *h) { return h->n_entries; } +int hashmap_reserve(Hashmap *h, unsigned entries_add) { + int r; + + assert(h); + + r = resize_buckets(h, entries_add); + if (r < 0) + return r; + + return 0; +} + char **hashmap_get_strv(Hashmap *h) { char **sv; Iterator it; -- cgit v1.2.3-54-g00ecf