git/hashmap.c
Jeff Hostetler 0607e10009 hashmap: add disallow_rehash setting
Teach hashmap to allow rehashes to be suppressed.
This is useful when hashmaps are accessed by multiple
threads.  It still requires the caller to properly
manage their locking.  This just prevents unexpected
rehashing during inserts and deletes.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-03-22 13:41:41 -07:00

293 lines
6.8 KiB
C

/*
* Generic implementation of hash-based key value mappings.
*/
#include "cache.h"
#include "hashmap.h"
#define FNV32_BASE ((unsigned int) 0x811c9dc5)
#define FNV32_PRIME ((unsigned int) 0x01000193)
unsigned int strhash(const char *str)
{
unsigned int c, hash = FNV32_BASE;
while ((c = (unsigned char) *str++))
hash = (hash * FNV32_PRIME) ^ c;
return hash;
}
unsigned int strihash(const char *str)
{
unsigned int c, hash = FNV32_BASE;
while ((c = (unsigned char) *str++)) {
if (c >= 'a' && c <= 'z')
c -= 'a' - 'A';
hash = (hash * FNV32_PRIME) ^ c;
}
return hash;
}
unsigned int memhash(const void *buf, size_t len)
{
unsigned int hash = FNV32_BASE;
unsigned char *ucbuf = (unsigned char *) buf;
while (len--) {
unsigned int c = *ucbuf++;
hash = (hash * FNV32_PRIME) ^ c;
}
return hash;
}
unsigned int memihash(const void *buf, size_t len)
{
unsigned int hash = FNV32_BASE;
unsigned char *ucbuf = (unsigned char *) buf;
while (len--) {
unsigned int c = *ucbuf++;
if (c >= 'a' && c <= 'z')
c -= 'a' - 'A';
hash = (hash * FNV32_PRIME) ^ c;
}
return hash;
}
/*
* Incoporate another chunk of data into a memihash
* computation.
*/
unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len)
{
unsigned int hash = hash_seed;
unsigned char *ucbuf = (unsigned char *) buf;
while (len--) {
unsigned int c = *ucbuf++;
if (c >= 'a' && c <= 'z')
c -= 'a' - 'A';
hash = (hash * FNV32_PRIME) ^ c;
}
return hash;
}
#define HASHMAP_INITIAL_SIZE 64
/* grow / shrink by 2^2 */
#define HASHMAP_RESIZE_BITS 2
/* load factor in percent */
#define HASHMAP_LOAD_FACTOR 80
static void alloc_table(struct hashmap *map, unsigned int size)
{
map->tablesize = size;
map->table = xcalloc(size, sizeof(struct hashmap_entry *));
/* calculate resize thresholds for new size */
map->grow_at = (unsigned int) ((uint64_t) size * HASHMAP_LOAD_FACTOR / 100);
if (size <= HASHMAP_INITIAL_SIZE)
map->shrink_at = 0;
else
/*
* The shrink-threshold must be slightly smaller than
* (grow-threshold / resize-factor) to prevent erratic resizing,
* thus we divide by (resize-factor + 1).
*/
map->shrink_at = map->grow_at / ((1 << HASHMAP_RESIZE_BITS) + 1);
}
static inline int entry_equals(const struct hashmap *map,
const struct hashmap_entry *e1, const struct hashmap_entry *e2,
const void *keydata)
{
return (e1 == e2) || (e1->hash == e2->hash && !map->cmpfn(e1, e2, keydata));
}
static inline unsigned int bucket(const struct hashmap *map,
const struct hashmap_entry *key)
{
return key->hash & (map->tablesize - 1);
}
int hashmap_bucket(const struct hashmap *map, unsigned int hash)
{
return hash & (map->tablesize - 1);
}
static void rehash(struct hashmap *map, unsigned int newsize)
{
unsigned int i, oldsize = map->tablesize;
struct hashmap_entry **oldtable = map->table;
if (map->disallow_rehash)
return;
alloc_table(map, newsize);
for (i = 0; i < oldsize; i++) {
struct hashmap_entry *e = oldtable[i];
while (e) {
struct hashmap_entry *next = e->next;
unsigned int b = bucket(map, e);
e->next = map->table[b];
map->table[b] = e;
e = next;
}
}
free(oldtable);
}
static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
const struct hashmap_entry *key, const void *keydata)
{
struct hashmap_entry **e = &map->table[bucket(map, key)];
while (*e && !entry_equals(map, *e, key, keydata))
e = &(*e)->next;
return e;
}
static int always_equal(const void *unused1, const void *unused2, const void *unused3)
{
return 0;
}
void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
size_t initial_size)
{
unsigned int size = HASHMAP_INITIAL_SIZE;
memset(map, 0, sizeof(*map));
map->cmpfn = equals_function ? equals_function : always_equal;
/* calculate initial table size and allocate the table */
initial_size = (unsigned int) ((uint64_t) initial_size * 100
/ HASHMAP_LOAD_FACTOR);
while (initial_size > size)
size <<= HASHMAP_RESIZE_BITS;
alloc_table(map, size);
}
void hashmap_free(struct hashmap *map, int free_entries)
{
if (!map || !map->table)
return;
if (free_entries) {
struct hashmap_iter iter;
struct hashmap_entry *e;
hashmap_iter_init(map, &iter);
while ((e = hashmap_iter_next(&iter)))
free(e);
}
free(map->table);
memset(map, 0, sizeof(*map));
}
void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
{
return *find_entry_ptr(map, key, keydata);
}
void *hashmap_get_next(const struct hashmap *map, const void *entry)
{
struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
for (; e; e = e->next)
if (entry_equals(map, entry, e, NULL))
return e;
return NULL;
}
void hashmap_add(struct hashmap *map, void *entry)
{
unsigned int b = bucket(map, entry);
/* add entry */
((struct hashmap_entry *) entry)->next = map->table[b];
map->table[b] = entry;
/* fix size and rehash if appropriate */
map->size++;
if (map->size > map->grow_at)
rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
}
void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
{
struct hashmap_entry *old;
struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
if (!*e)
return NULL;
/* remove existing entry */
old = *e;
*e = old->next;
old->next = NULL;
/* fix size and rehash if appropriate */
map->size--;
if (map->size < map->shrink_at)
rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
return old;
}
void *hashmap_put(struct hashmap *map, void *entry)
{
struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
hashmap_add(map, entry);
return old;
}
void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
{
iter->map = map;
iter->tablepos = 0;
iter->next = NULL;
}
void *hashmap_iter_next(struct hashmap_iter *iter)
{
struct hashmap_entry *current = iter->next;
for (;;) {
if (current) {
iter->next = current->next;
return current;
}
if (iter->tablepos >= iter->map->tablesize)
return NULL;
current = iter->map->table[iter->tablepos++];
}
}
struct pool_entry {
struct hashmap_entry ent;
size_t len;
unsigned char data[FLEX_ARRAY];
};
static int pool_entry_cmp(const struct pool_entry *e1,
const struct pool_entry *e2,
const unsigned char *keydata)
{
return e1->data != keydata &&
(e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
}
const void *memintern(const void *data, size_t len)
{
static struct hashmap map;
struct pool_entry key, *e;
/* initialize string pool hashmap */
if (!map.tablesize)
hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, 0);
/* lookup interned string in pool */
hashmap_entry_init(&key, memhash(data, len));
key.len = len;
e = hashmap_get(&map, &key, data);
if (!e) {
/* not found: create it */
FLEX_ALLOC_MEM(e, data, data, len);
hashmap_entry_init(e, key.ent.hash);
e->len = len;
hashmap_add(&map, e);
}
return e->data;
}