mirror of
https://github.com/git/git
synced 2024-08-27 19:49:21 +00:00
![Jeff Hostetler](/assets/img/avatar_default.png)
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
/*
|
|
* 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(map->cmpfn_data, 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;
|
|
|
|
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 *unused_cmp_data,
|
|
const void *unused1,
|
|
const void *unused2,
|
|
const void *unused_keydata)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
|
|
const void *cmpfn_data, size_t initial_size)
|
|
{
|
|
unsigned int size = HASHMAP_INITIAL_SIZE;
|
|
|
|
memset(map, 0, sizeof(*map));
|
|
|
|
map->cmpfn = equals_function ? equals_function : always_equal;
|
|
map->cmpfn_data = cmpfn_data;
|
|
|
|
/* 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);
|
|
|
|
/*
|
|
* Keep track of the number of items in the map and
|
|
* allow the map to automatically grow as necessary.
|
|
*/
|
|
map->do_count_items = 1;
|
|
}
|
|
|
|
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 */
|
|
if (map->do_count_items) {
|
|
map->private_size++;
|
|
if (map->private_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 */
|
|
if (map->do_count_items) {
|
|
map->private_size--;
|
|
if (map->private_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 void *unused_cmp_data,
|
|
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, NULL, 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;
|
|
}
|