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git/hashmap.h

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#ifndef HASHMAP_H
#define HASHMAP_H
#include "hash.h"
/*
* Generic implementation of hash-based key-value mappings.
*
* An example that maps long to a string:
* For the sake of the example this allows to lookup exact values, too
* (i.e. it is operated as a set, the value is part of the key)
* -------------------------------------
*
* struct hashmap map;
* struct long2string {
* struct hashmap_entry ent;
* long key;
* char value[FLEX_ARRAY]; // be careful with allocating on stack!
* };
*
* #define COMPARE_VALUE 1
*
* static int long2string_cmp(const void *hashmap_cmp_fn_data,
* const struct hashmap_entry *eptr,
* const struct hashmap_entry *entry_or_key,
* const void *keydata)
* {
* const char *string = keydata;
* unsigned flags = *(unsigned *)hashmap_cmp_fn_data;
* const struct long2string *e1, *e2;
*
* e1 = container_of(eptr, const struct long2string, ent);
* e2 = container_of(entry_or_key, const struct long2string, ent);
*
* if (flags & COMPARE_VALUE)
* return e1->key != e2->key ||
* strcmp(e1->value, string ? string : e2->value);
* else
* return e1->key != e2->key;
* }
*
* int main(int argc, char **argv)
* {
* long key;
* char value[255], action[32];
* unsigned flags = 0;
*
* hashmap_init(&map, long2string_cmp, &flags, 0);
*
* while (scanf("%s %ld %s", action, &key, value)) {
*
* if (!strcmp("add", action)) {
* struct long2string *e;
* FLEX_ALLOC_STR(e, value, value);
* hashmap_entry_init(&e->ent, memhash(&key, sizeof(long)));
* e->key = key;
* hashmap_add(&map, &e->ent);
* }
*
* if (!strcmp("print_all_by_key", action)) {
* struct long2string k, *e;
* hashmap_entry_init(&k.ent, memhash(&key, sizeof(long)));
* k.key = key;
*
* flags &= ~COMPARE_VALUE;
* e = hashmap_get_entry(&map, &k, ent, NULL);
* if (e) {
* printf("first: %ld %s\n", e->key, e->value);
* while ((e = hashmap_get_next_entry(&map, e,
* struct long2string, ent))) {
* printf("found more: %ld %s\n", e->key, e->value);
* }
* }
* }
*
* if (!strcmp("has_exact_match", action)) {
* struct long2string *e;
* FLEX_ALLOC_STR(e, value, value);
* hashmap_entry_init(&e->ent, memhash(&key, sizeof(long)));
* e->key = key;
*
* flags |= COMPARE_VALUE;
* printf("%sfound\n",
* hashmap_get(&map, &e->ent, NULL) ? "" : "not ");
* free(e);
* }
*
* if (!strcmp("has_exact_match_no_heap_alloc", action)) {
* struct long2string k;
* hashmap_entry_init(&k.ent, memhash(&key, sizeof(long)));
* k.key = key;
*
* flags |= COMPARE_VALUE;
* printf("%sfound\n",
* hashmap_get(&map, &k.ent, value) ? "" : "not ");
* }
*
* if (!strcmp("end", action)) {
* hashmap_clear_and_free(&map, struct long2string, ent);
* break;
* }
* }
*
* return 0;
* }
*/
/*
* Ready-to-use hash functions for strings, using the FNV-1 algorithm (see
* http://www.isthe.com/chongo/tech/comp/fnv).
* `strhash` and `strihash` take 0-terminated strings, while `memhash` and
* `memihash` operate on arbitrary-length memory.
* `strihash` and `memihash` are case insensitive versions.
* `memihash_cont` is a variant of `memihash` that allows a computation to be
* continued with another chunk of data.
*/
unsigned int strhash(const char *buf);
unsigned int strihash(const char *buf);
unsigned int memhash(const void *buf, size_t len);
unsigned int memihash(const void *buf, size_t len);
unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
/*
* Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
* for use in hash tables. Cryptographic hashes are supposed to have
* uniform distribution, so in contrast to `memhash()`, this just copies
* the first `sizeof(int)` bytes without shuffling any bits. Note that
* the results will be different on big-endian and little-endian
* platforms, so they should not be stored or transferred over the net.
*/
static inline unsigned int oidhash(const struct object_id *oid)
{
/*
* Equivalent to 'return *(unsigned int *)oid->hash;', but safe on
* platforms that don't support unaligned reads.
*/
unsigned int hash;
memcpy(&hash, oid->hash, sizeof(hash));
return hash;
}
/*
* struct hashmap_entry is an opaque structure representing an entry in the
* hash table.
* Ideally it should be followed by an int-sized member to prevent unused
* memory on 64-bit systems due to alignment.
*/
struct hashmap_entry {
/*
* next points to the next entry in case of collisions (i.e. if
* multiple entries map to the same bucket)
*/
struct hashmap_entry *next;
/* entry's hash code */
unsigned int hash;
};
/*
* User-supplied function to test two hashmap entries for equality. Shall
* return 0 if the entries are equal.
*
* This function is always called with non-NULL `entry` and `entry_or_key`
* parameters that have the same hash code.
*
* When looking up an entry, the `key` and `keydata` parameters to hashmap_get
* and hashmap_remove are always passed as second `entry_or_key` and third
* argument `keydata`, respectively. Otherwise, `keydata` is NULL.
*
* When it is too expensive to allocate a user entry (either because it is
* large or variable sized, such that it is not on the stack), then the
* relevant data to check for equality should be passed via `keydata`.
* In this case `key` can be a stripped down version of the user key data
* or even just a hashmap_entry having the correct hash.
*
* The `hashmap_cmp_fn_data` entry is the pointer given in the init function.
*/
typedef int (*hashmap_cmp_fn)(const void *hashmap_cmp_fn_data,
const struct hashmap_entry *entry,
const struct hashmap_entry *entry_or_key,
const void *keydata);
/*
* struct hashmap is the hash table structure. Members can be used as follows,
* but should not be modified directly.
*/
struct hashmap {
struct hashmap_entry **table;
/* Stores the comparison function specified in `hashmap_init()`. */
hashmap_cmp_fn cmpfn;
const void *cmpfn_data;
/* total number of entries (0 means the hashmap is empty) */
unsigned int private_size; /* use hashmap_get_size() */
/*
* tablesize is the allocated size of the hash table. A non-0 value
* indicates that the hashmap is initialized. It may also be useful
* for statistical purposes (i.e. `size / tablesize` is the current
* load factor).
*/
unsigned int tablesize;
unsigned int grow_at;
unsigned int shrink_at;
unsigned int do_count_items : 1;
};
/* hashmap functions */
#define HASHMAP_INIT(fn, data) { .cmpfn = fn, .cmpfn_data = data, \
.do_count_items = 1 }
/*
* Initializes a hashmap structure.
*
* `map` is the hashmap to initialize.
*
* The `equals_function` can be specified to compare two entries for equality.
* If NULL, entries are considered equal if their hash codes are equal.
*
* The `equals_function_data` parameter can be used to provide additional data
* (a callback cookie) that will be passed to `equals_function` each time it
* is called. This allows a single `equals_function` to implement multiple
* comparison functions.
*
* If the total number of entries is known in advance, the `initial_size`
* parameter may be used to preallocate a sufficiently large table and thus
* prevent expensive resizing. If 0, the table is dynamically resized.
*/
void hashmap_init(struct hashmap *map,
hashmap_cmp_fn equals_function,
const void *equals_function_data,
size_t initial_size);
/* internal functions for clearing or freeing hashmap */
void hashmap_partial_clear_(struct hashmap *map, ssize_t offset);
void hashmap_clear_(struct hashmap *map, ssize_t offset);
/*
* Frees a hashmap structure and allocated memory for the table, but does not
* free the entries nor anything they point to.
*
* Usage note:
*
* Many callers will need to iterate over all entries and free the data each
* entry points to; in such a case, they can free the entry itself while at it.
* Thus, you might see:
*
* hashmap_for_each_entry(map, hashmap_iter, e, hashmap_entry_name) {
* free(e->somefield);
* free(e);
* }
* hashmap_clear(map);
*
* instead of
*
* hashmap_for_each_entry(map, hashmap_iter, e, hashmap_entry_name) {
* free(e->somefield);
* }
* hashmap_clear_and_free(map, struct my_entry_struct, hashmap_entry_name);
*
* to avoid the implicit extra loop over the entries. However, if there are
* no special fields in your entry that need to be freed beyond the entry
* itself, it is probably simpler to avoid the explicit loop and just call
* hashmap_clear_and_free().
*/
#define hashmap_clear(map) hashmap_clear_(map, -1)
/*
* Similar to hashmap_clear(), except that the table is no deallocated; it
* is merely zeroed out but left the same size as before. If the hashmap
* will be reused, this avoids the overhead of deallocating and
* reallocating map->table. As with hashmap_clear(), you may need to free
* the entries yourself before calling this function.
*/
#define hashmap_partial_clear(map) hashmap_partial_clear_(map, -1)
/*
* Similar to hashmap_clear() but also frees all entries. @type is the
* struct type of the entry where @member is the hashmap_entry struct used
* to associate with @map.
*
* See usage note above hashmap_clear().
*/
#define hashmap_clear_and_free(map, type, member) \
hashmap_clear_(map, offsetof(type, member))
/*
* Similar to hashmap_partial_clear() but also frees all entries. @type is
* the struct type of the entry where @member is the hashmap_entry struct
* used to associate with @map.
*
* See usage note above hashmap_clear().
*/
#define hashmap_partial_clear_and_free(map, type, member) \
hashmap_partial_clear_(map, offsetof(type, member))
/* hashmap_entry functions */
/*
* Initializes a hashmap_entry structure.
*
* `entry` points to the entry to initialize.
* `hash` is the hash code of the entry.
*
* The hashmap_entry structure does not hold references to external resources,
* and it is safe to just discard it once you are done with it (i.e. if
* your structure was allocated with xmalloc(), you can just free(3) it,
* and if it is on stack, you can just let it go out of scope).
*/
static inline void hashmap_entry_init(struct hashmap_entry *e,
unsigned int hash)
{
e->hash = hash;
e->next = NULL;
}
/*
* Return the number of items in the map.
*/
static inline unsigned int hashmap_get_size(struct hashmap *map)
{
if (map->do_count_items)
return map->private_size;
BUG("hashmap_get_size: size not set");
return 0;
}
/*
* Returns the hashmap entry for the specified key, or NULL if not found.
*
* `map` is the hashmap structure.
*
* `key` is a user data structure that starts with hashmap_entry that has at
* least been initialized with the proper hash code (via `hashmap_entry_init`).
*
* `keydata` is a data structure that holds just enough information to check
* for equality to a given entry.
*
* If the key data is variable-sized (e.g. a FLEX_ARRAY string) or quite large,
* it is undesirable to create a full-fledged entry structure on the heap and
* copy all the key data into the structure.
*
* In this case, the `keydata` parameter can be used to pass
* variable-sized key data directly to the comparison function, and the `key`
* parameter can be a stripped-down, fixed size entry structure allocated on the
* stack.
*
* If an entry with matching hash code is found, `key` and `keydata` are passed
* to `hashmap_cmp_fn` to decide whether the entry matches the key.
*/
struct hashmap_entry *hashmap_get(const struct hashmap *map,
const struct hashmap_entry *key,
const void *keydata);
/*
* Returns the hashmap entry for the specified hash code and key data,
* or NULL if not found.
*
* `map` is the hashmap structure.
* `hash` is the hash code of the entry to look up.
*
* If an entry with matching hash code is found, `keydata` is passed to
* `hashmap_cmp_fn` to decide whether the entry matches the key. The
* `entry_or_key` parameter of `hashmap_cmp_fn` points to a hashmap_entry
* structure that should not be used in the comparison.
*/
static inline struct hashmap_entry *hashmap_get_from_hash(
const struct hashmap *map,
unsigned int hash,
const void *keydata)
{
struct hashmap_entry key;
hashmap_entry_init(&key, hash);
return hashmap_get(map, &key, keydata);
}
/*
* Returns the next equal hashmap entry, or NULL if not found. This can be
* used to iterate over duplicate entries (see `hashmap_add`).
*
* `map` is the hashmap structure.
* `entry` is the hashmap_entry to start the search from, obtained via a previous
* call to `hashmap_get` or `hashmap_get_next`.
*/
struct hashmap_entry *hashmap_get_next(const struct hashmap *map,
const struct hashmap_entry *entry);
/*
* Adds a hashmap entry. This allows to add duplicate entries (i.e.
* separate values with the same key according to hashmap_cmp_fn).
*
* `map` is the hashmap structure.
* `entry` is the entry to add.
*/
void hashmap_add(struct hashmap *map, struct hashmap_entry *entry);
/*
* Adds or replaces a hashmap entry. If the hashmap contains duplicate
* entries equal to the specified entry, only one of them will be replaced.
*
* `map` is the hashmap structure.
* `entry` is the entry to add or replace.
* Returns the replaced entry, or NULL if not found (i.e. the entry was added).
*/
struct hashmap_entry *hashmap_put(struct hashmap *map,
struct hashmap_entry *entry);
/*
* Adds or replaces a hashmap entry contained within @keyvar,
* where @keyvar is a pointer to a struct containing a
* "struct hashmap_entry" @member.
*
* Returns the replaced pointer which is of the same type as @keyvar,
* or NULL if not found.
*/
#define hashmap_put_entry(map, keyvar, member) \
container_of_or_null_offset(hashmap_put(map, &(keyvar)->member), \
OFFSETOF_VAR(keyvar, member))
/*
* Removes a hashmap entry matching the specified key. If the hashmap contains
* duplicate entries equal to the specified key, only one of them will be
* removed. Returns the removed entry, or NULL if not found.
*
* Argument explanation is the same as in `hashmap_get`.
*/
struct hashmap_entry *hashmap_remove(struct hashmap *map,
const struct hashmap_entry *key,
const void *keydata);
/*
* Removes a hashmap entry contained within @keyvar,
* where @keyvar is a pointer to a struct containing a
* "struct hashmap_entry" @member.
*
* See `hashmap_get` for an explanation of @keydata
*
* Returns the replaced pointer which is of the same type as @keyvar,
* or NULL if not found.
*/
#define hashmap_remove_entry(map, keyvar, member, keydata) \
container_of_or_null_offset( \
hashmap_remove(map, &(keyvar)->member, keydata), \
OFFSETOF_VAR(keyvar, member))
/*
* Returns the `bucket` an entry is stored in.
* Useful for multithreaded read access.
*/
int hashmap_bucket(const struct hashmap *map, unsigned int hash);
/*
* Used to iterate over all entries of a hashmap. Note that it is
* not safe to add or remove entries to the hashmap while
* iterating.
*/
struct hashmap_iter {
struct hashmap *map;
struct hashmap_entry *next;
unsigned int tablepos;
};
/* Initializes a `hashmap_iter` structure. */
void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter);
/* Returns the next hashmap_entry, or NULL if there are no more entries. */
struct hashmap_entry *hashmap_iter_next(struct hashmap_iter *iter);
/* Initializes the iterator and returns the first entry, if any. */
static inline struct hashmap_entry *hashmap_iter_first(struct hashmap *map,
struct hashmap_iter *iter)
{
hashmap_iter_init(map, iter);
return hashmap_iter_next(iter);
}
/*
* returns the first entry in @map using @iter, where the entry is of
* @type (e.g. "struct foo") and @member is the name of the
* "struct hashmap_entry" in @type
*/
#define hashmap_iter_first_entry(map, iter, type, member) \
container_of_or_null(hashmap_iter_first(map, iter), type, member)
/* internal macro for hashmap_for_each_entry */
#define hashmap_iter_next_entry_offset(iter, offset) \
container_of_or_null_offset(hashmap_iter_next(iter), offset)
/* internal macro for hashmap_for_each_entry */
#define hashmap_iter_first_entry_offset(map, iter, offset) \
container_of_or_null_offset(hashmap_iter_first(map, iter), offset)
/*
* iterate through @map using @iter, @var is a pointer to a type
* containing a @member which is a "struct hashmap_entry"
*/
#define hashmap_for_each_entry(map, iter, var, member) \
for (var = NULL, /* for systems without typeof */ \
var = hashmap_iter_first_entry_offset(map, iter, \
OFFSETOF_VAR(var, member)); \
var; \
var = hashmap_iter_next_entry_offset(iter, \
OFFSETOF_VAR(var, member)))
/*
* returns a pointer of type matching @keyvar, or NULL if nothing found.
* @keyvar is a pointer to a struct containing a
* "struct hashmap_entry" @member.
*/
#define hashmap_get_entry(map, keyvar, member, keydata) \
container_of_or_null_offset( \
hashmap_get(map, &(keyvar)->member, keydata), \
OFFSETOF_VAR(keyvar, member))
#define hashmap_get_entry_from_hash(map, hash, keydata, type, member) \
container_of_or_null(hashmap_get_from_hash(map, hash, keydata), \
type, member)
/*
* returns the next equal pointer to @var, or NULL if not found.
* @var is a pointer of any type containing "struct hashmap_entry"
* @member is the name of the "struct hashmap_entry" field
*/
#define hashmap_get_next_entry(map, var, member) \
container_of_or_null_offset(hashmap_get_next(map, &(var)->member), \
OFFSETOF_VAR(var, member))
/*
* iterate @map starting from @var, where @var is a pointer of @type
* and @member is the name of the "struct hashmap_entry" field in @type
*/
#define hashmap_for_each_entry_from(map, var, member) \
for (; \
var; \
var = hashmap_get_next_entry(map, var, member))
/*
* Disable item counting and automatic rehashing when adding/removing items.
*
* Normally, the hashmap keeps track of the number of items in the map
* and uses it to dynamically resize it. This (both the counting and
* the resizing) can cause problems when the map is being used by
* threaded callers (because the hashmap code does not know about the
* locking strategy used by the threaded callers and therefore, does
* not know how to protect the "private_size" counter).
*/
static inline void hashmap_disable_item_counting(struct hashmap *map)
{
map->do_count_items = 0;
}
/*
* Re-enable item counting when adding/removing items.
* If counting is currently disabled, it will force count them.
* It WILL NOT automatically rehash them.
*/
static inline void hashmap_enable_item_counting(struct hashmap *map)
{
unsigned int n = 0;
struct hashmap_iter iter;
if (map->do_count_items)
return;
hashmap_iter_init(map, &iter);
while (hashmap_iter_next(&iter))
n++;
map->do_count_items = 1;
map->private_size = n;
}
/* String interning */
/*
* Returns the unique, interned version of the specified string or data,
* similar to the `String.intern` API in Java and .NET, respectively.
* Interned strings remain valid for the entire lifetime of the process.
*
* Can be used as `[x]strdup()` or `xmemdupz` replacement, except that interned
* strings / data must not be modified or freed.
*
* Interned strings are best used for short strings with high probability of
* duplicates.
*
* Uses a hashmap to store the pool of interned strings.
*/
const void *memintern(const void *data, size_t len);
static inline const char *strintern(const char *string)
{
return memintern(string, strlen(string));
}
#endif