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Special-case size-1 sequential hopscotch hash table

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Rather than allocate a HH_HOP_RANGE large array of buckets, allocate
just 1 if the initial size is 1, then jump to HH_HOP_RANGE as soon as a
second element is added to the table.  There are quite a few cases where
hash tables are created where there never be more than 1 (or even 0)
elements in the table (e.g., a writer without readers, a reader for a
keyless topic).

Signed-off-by: Erik Boasson <eb@ilities.com>
This commit is contained in:
Erik Boasson 2019-06-24 10:05:00 +02:00 • committed by eboasson
parent 0b8fd9fcc0
commit 0e888eb2ec
2 changed files with 55 additions and 29 deletions
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4
src/core/ddsc/src/dds_whc.c
View file

@ -366,11 +366,11 @@ struct whc *whc_new (int is_transient_local, uint32_t hdepth, uint32_t tldepth)
#if USE_EHH
whc->seq_hash = ddsrt_ehh_new (sizeof (struct whc_seq_entry), 32, whc_seq_entry_hash, whc_seq_entry_eq);
#else
whc->seq_hash = ddsrt_hh_new (32, whc_node_hash, whc_node_eq);
whc->seq_hash = ddsrt_hh_new (1, whc_node_hash, whc_node_eq);
#endif
if (whc->idxdepth > 0)
whc->idx_hash = ddsrt_hh_new (32, whc_idxnode_hash_key, whc_idxnode_eq_key);
whc->idx_hash = ddsrt_hh_new (1, whc_idxnode_hash_key, whc_idxnode_eq_key);
else
whc->idx_hash = NULL;

28
src/ddsrt/src/hopscotch.c
View file

@ -39,11 +39,17 @@ struct ddsrt_hh {
static void ddsrt_hh_init (struct ddsrt_hh *rt, uint32_t init_size, ddsrt_hh_hash_fn hash, ddsrt_hh_equals_fn equals)
{
uint32_t size = HH_HOP_RANGE;
uint32_t size;
uint32_t i;
/* degenerate case to minimize memory use */
if (init_size == 1) {
size = 1;
} else {
size = HH_HOP_RANGE;
while (size < init_size) {
size *= 2;
}
}
rt->hash = hash;
rt->equals = equals;
rt->size = size;
@ -125,6 +131,25 @@ static uint32_t ddsrt_hh_find_closer_free_bucket (struct ddsrt_hh *rt, uint32_t
static void ddsrt_hh_resize (struct ddsrt_hh *rt)
{
if (rt->size == 1) {
assert (rt->size == 1);
assert (rt->buckets[0].hopinfo == 1);
assert (rt->buckets[0].data != NULL);
rt->size = HH_HOP_RANGE;
const uint32_t hash = rt->hash (rt->buckets[0].data);
const uint32_t idxmask = rt->size - 1;
const uint32_t start_bucket = hash & idxmask;
struct ddsrt_hh_bucket *newbs = ddsrt_malloc (rt->size * sizeof (*newbs));
for (uint32_t i = 0; i < rt->size; i++) {
newbs[i].hopinfo = 0;
newbs[i].data = NULL;
}
newbs[start_bucket] = rt->buckets[0];
ddsrt_free (rt->buckets);
rt->buckets = newbs;
} else {
struct ddsrt_hh_bucket *bs1;
uint32_t i, idxmask0, idxmask1;
@ -153,6 +178,7 @@ static void ddsrt_hh_resize (struct ddsrt_hh *rt)
ddsrt_free (rt->buckets);
rt->size *= 2;
rt->buckets = bs1;
}
}
int ddsrt_hh_add (struct ddsrt_hh * __restrict rt, const void * __restrict data)