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8b604d1951
This is to address concerns raised by ThreadSanitizer on the mailing list
about threaded unprotected R/W access to map.size with my previous "disallow
rehash" change (0607e10009
).
See:
https://public-inbox.org/git/adb37b70139fd1e2bac18bfd22c8b96683ae18eb.1502780344.git.martin.agren@gmail.com/
Add API to hashmap to disable item counting and thus automatic rehashing.
Also include API to later re-enable them.
When item counting is disabled, the map.size field is invalid. So to
prevent accidents, the field has been renamed and an accessor function
hashmap_get_size() has been added. All direct references to this
field have been been updated. And the name of the field changed
to map.private_size to communicate this.
Here is the relevant output from ThreadSanitizer showing the problem:
WARNING: ThreadSanitizer: data race (pid=10554)
Read of size 4 at 0x00000082d488 by thread T2 (mutexes: write M16):
#0 hashmap_add hashmap.c:209
#1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
#2 handle_range_dir name-hash.c:347
#3 handle_range_1 name-hash.c:415
#4 lazy_dir_thread_proc name-hash.c:471
#5 <null> <null>
Previous write of size 4 at 0x00000082d488 by thread T1 (mutexes: write M31):
#0 hashmap_add hashmap.c:209
#1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
#2 handle_range_dir name-hash.c:347
#3 handle_range_1 name-hash.c:415
#4 handle_range_dir name-hash.c:380
#5 handle_range_1 name-hash.c:415
#6 lazy_dir_thread_proc name-hash.c:471
#7 <null> <null>
Martin gives instructions for running TSan on test t3008 in this post:
https://public-inbox.org/git/CAN0heSoJDL9pWELD6ciLTmWf-a=oyxe4EXXOmCKvsG5MSuzxsA@mail.gmail.com/
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
308 lines
7.2 KiB
C
308 lines
7.2 KiB
C
/*
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* Generic implementation of hash-based key value mappings.
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*/
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#include "cache.h"
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#include "hashmap.h"
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#define FNV32_BASE ((unsigned int) 0x811c9dc5)
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#define FNV32_PRIME ((unsigned int) 0x01000193)
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unsigned int strhash(const char *str)
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{
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unsigned int c, hash = FNV32_BASE;
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while ((c = (unsigned char) *str++))
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hash = (hash * FNV32_PRIME) ^ c;
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return hash;
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}
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unsigned int strihash(const char *str)
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{
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unsigned int c, hash = FNV32_BASE;
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while ((c = (unsigned char) *str++)) {
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if (c >= 'a' && c <= 'z')
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c -= 'a' - 'A';
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hash = (hash * FNV32_PRIME) ^ c;
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}
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return hash;
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}
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unsigned int memhash(const void *buf, size_t len)
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{
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unsigned int hash = FNV32_BASE;
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unsigned char *ucbuf = (unsigned char *) buf;
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while (len--) {
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unsigned int c = *ucbuf++;
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hash = (hash * FNV32_PRIME) ^ c;
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}
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return hash;
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}
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unsigned int memihash(const void *buf, size_t len)
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{
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unsigned int hash = FNV32_BASE;
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unsigned char *ucbuf = (unsigned char *) buf;
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while (len--) {
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unsigned int c = *ucbuf++;
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if (c >= 'a' && c <= 'z')
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c -= 'a' - 'A';
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hash = (hash * FNV32_PRIME) ^ c;
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}
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return hash;
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}
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/*
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* Incoporate another chunk of data into a memihash
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* computation.
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*/
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unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len)
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{
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unsigned int hash = hash_seed;
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unsigned char *ucbuf = (unsigned char *) buf;
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while (len--) {
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unsigned int c = *ucbuf++;
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if (c >= 'a' && c <= 'z')
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c -= 'a' - 'A';
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hash = (hash * FNV32_PRIME) ^ c;
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}
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return hash;
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}
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#define HASHMAP_INITIAL_SIZE 64
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/* grow / shrink by 2^2 */
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#define HASHMAP_RESIZE_BITS 2
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/* load factor in percent */
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#define HASHMAP_LOAD_FACTOR 80
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static void alloc_table(struct hashmap *map, unsigned int size)
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{
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map->tablesize = size;
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map->table = xcalloc(size, sizeof(struct hashmap_entry *));
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/* calculate resize thresholds for new size */
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map->grow_at = (unsigned int) ((uint64_t) size * HASHMAP_LOAD_FACTOR / 100);
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if (size <= HASHMAP_INITIAL_SIZE)
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map->shrink_at = 0;
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else
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/*
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* The shrink-threshold must be slightly smaller than
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* (grow-threshold / resize-factor) to prevent erratic resizing,
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* thus we divide by (resize-factor + 1).
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*/
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map->shrink_at = map->grow_at / ((1 << HASHMAP_RESIZE_BITS) + 1);
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}
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static inline int entry_equals(const struct hashmap *map,
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const struct hashmap_entry *e1, const struct hashmap_entry *e2,
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const void *keydata)
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{
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return (e1 == e2) ||
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(e1->hash == e2->hash &&
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!map->cmpfn(map->cmpfn_data, e1, e2, keydata));
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}
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static inline unsigned int bucket(const struct hashmap *map,
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const struct hashmap_entry *key)
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{
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return key->hash & (map->tablesize - 1);
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}
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int hashmap_bucket(const struct hashmap *map, unsigned int hash)
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{
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return hash & (map->tablesize - 1);
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}
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static void rehash(struct hashmap *map, unsigned int newsize)
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{
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unsigned int i, oldsize = map->tablesize;
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struct hashmap_entry **oldtable = map->table;
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alloc_table(map, newsize);
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for (i = 0; i < oldsize; i++) {
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struct hashmap_entry *e = oldtable[i];
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while (e) {
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struct hashmap_entry *next = e->next;
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unsigned int b = bucket(map, e);
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e->next = map->table[b];
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map->table[b] = e;
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e = next;
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}
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}
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free(oldtable);
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}
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static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
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const struct hashmap_entry *key, const void *keydata)
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{
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struct hashmap_entry **e = &map->table[bucket(map, key)];
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while (*e && !entry_equals(map, *e, key, keydata))
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e = &(*e)->next;
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return e;
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}
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static int always_equal(const void *unused_cmp_data,
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const void *unused1,
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const void *unused2,
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const void *unused_keydata)
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{
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return 0;
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}
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void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
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const void *cmpfn_data, size_t initial_size)
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{
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unsigned int size = HASHMAP_INITIAL_SIZE;
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memset(map, 0, sizeof(*map));
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map->cmpfn = equals_function ? equals_function : always_equal;
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map->cmpfn_data = cmpfn_data;
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/* calculate initial table size and allocate the table */
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initial_size = (unsigned int) ((uint64_t) initial_size * 100
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/ HASHMAP_LOAD_FACTOR);
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while (initial_size > size)
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size <<= HASHMAP_RESIZE_BITS;
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alloc_table(map, size);
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/*
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* Keep track of the number of items in the map and
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* allow the map to automatically grow as necessary.
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*/
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map->do_count_items = 1;
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}
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void hashmap_free(struct hashmap *map, int free_entries)
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{
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if (!map || !map->table)
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return;
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if (free_entries) {
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struct hashmap_iter iter;
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struct hashmap_entry *e;
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hashmap_iter_init(map, &iter);
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while ((e = hashmap_iter_next(&iter)))
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free(e);
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}
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free(map->table);
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memset(map, 0, sizeof(*map));
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}
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void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
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{
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return *find_entry_ptr(map, key, keydata);
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}
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void *hashmap_get_next(const struct hashmap *map, const void *entry)
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{
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struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
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for (; e; e = e->next)
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if (entry_equals(map, entry, e, NULL))
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return e;
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return NULL;
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}
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void hashmap_add(struct hashmap *map, void *entry)
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{
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unsigned int b = bucket(map, entry);
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/* add entry */
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((struct hashmap_entry *) entry)->next = map->table[b];
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map->table[b] = entry;
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/* fix size and rehash if appropriate */
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if (map->do_count_items) {
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map->private_size++;
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if (map->private_size > map->grow_at)
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rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
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}
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}
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void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
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{
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struct hashmap_entry *old;
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struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
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if (!*e)
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return NULL;
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/* remove existing entry */
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old = *e;
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*e = old->next;
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old->next = NULL;
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/* fix size and rehash if appropriate */
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if (map->do_count_items) {
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map->private_size--;
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if (map->private_size < map->shrink_at)
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rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
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}
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return old;
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}
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void *hashmap_put(struct hashmap *map, void *entry)
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{
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struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
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hashmap_add(map, entry);
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return old;
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}
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void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
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{
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iter->map = map;
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iter->tablepos = 0;
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iter->next = NULL;
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}
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void *hashmap_iter_next(struct hashmap_iter *iter)
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{
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struct hashmap_entry *current = iter->next;
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for (;;) {
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if (current) {
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iter->next = current->next;
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return current;
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}
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if (iter->tablepos >= iter->map->tablesize)
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return NULL;
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current = iter->map->table[iter->tablepos++];
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}
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}
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struct pool_entry {
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struct hashmap_entry ent;
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size_t len;
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unsigned char data[FLEX_ARRAY];
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};
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static int pool_entry_cmp(const void *unused_cmp_data,
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const struct pool_entry *e1,
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const struct pool_entry *e2,
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const unsigned char *keydata)
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{
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return e1->data != keydata &&
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(e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
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}
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const void *memintern(const void *data, size_t len)
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{
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static struct hashmap map;
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struct pool_entry key, *e;
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/* initialize string pool hashmap */
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if (!map.tablesize)
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hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, NULL, 0);
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/* lookup interned string in pool */
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hashmap_entry_init(&key, memhash(data, len));
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key.len = len;
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e = hashmap_get(&map, &key, data);
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if (!e) {
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/* not found: create it */
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FLEX_ALLOC_MEM(e, data, data, len);
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hashmap_entry_init(e, key.ent.hash);
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e->len = len;
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hashmap_add(&map, e);
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}
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return e->data;
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}
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