This is similar to using the hashmap in hashmap.c, but with an easier-to-use API. In particular, custom entry comparisons no longer need to be written, and lookups can be done without constructing a temporary entry structure.
oidset has been updated to use oidmap. Signed-off-by: Jonathan Tan <jonathanta...@google.com> --- I have been wishing for an OID map for a while, and it seems to me that Jeff Hostetler's recent patches [1] could use one too, so here it is. (Also, I wonder if some details such as grow_at, shrink_at, and do_count_items can be removed, since the applications of this are narrower than that of hashmap.) [1] https://public-inbox.org/git/20170922202632.53714-1-...@jeffhostetler.com/ --- Makefile | 1 + oidmap.c | 152 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ oidmap.h | 98 ++++++++++++++++++++++++++++++++++++++++ oidset.c | 38 ++++------------ oidset.h | 4 +- 5 files changed, 263 insertions(+), 30 deletions(-) create mode 100644 oidmap.c create mode 100644 oidmap.h diff --git a/Makefile b/Makefile index ed4ca438b..64136dde4 100644 --- a/Makefile +++ b/Makefile @@ -821,6 +821,7 @@ LIB_OBJS += notes-cache.o LIB_OBJS += notes-merge.o LIB_OBJS += notes-utils.o LIB_OBJS += object.o +LIB_OBJS += oidmap.o LIB_OBJS += oidset.o LIB_OBJS += packfile.o LIB_OBJS += pack-bitmap.o diff --git a/oidmap.c b/oidmap.c new file mode 100644 index 000000000..40e696cee --- /dev/null +++ b/oidmap.c @@ -0,0 +1,152 @@ +#include "cache.h" +#include "oidmap.h" + +#define OIDMAP_INITIAL_SIZE 64 +/* grow / shrink by 2^2 */ +#define OIDMAP_RESIZE_BITS 2 +/* load factor in percent */ +#define OIDMAP_LOAD_FACTOR 80 + +static void alloc_table(struct oidmap *map, unsigned int size) +{ + map->tablesize = size; + map->table = xcalloc(size, sizeof(struct oidmap_entry *)); + + /* calculate resize thresholds for new size */ + map->grow_at = (unsigned int) ((uint64_t) size * OIDMAP_LOAD_FACTOR / 100); + if (size <= OIDMAP_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 << OIDMAP_RESIZE_BITS) + 1); +} + +static inline unsigned int bucket(const struct oidmap *map, + const struct object_id *key) +{ + unsigned int hash; + memcpy(&hash, key->hash, sizeof(hash)); + return hash & (map->tablesize - 1); +} + +static void rehash(struct oidmap *map, unsigned int newsize) +{ + unsigned int i, oldsize = map->tablesize; + struct oidmap_entry **oldtable = map->table; + + alloc_table(map, newsize); + for (i = 0; i < oldsize; i++) { + struct oidmap_entry *e = oldtable[i]; + while (e) { + struct oidmap_entry *next = e->next; + unsigned int b = bucket(map, &e->oid); + e->next = map->table[b]; + map->table[b] = e; + e = next; + } + } + free(oldtable); +} + +static inline struct oidmap_entry **find_entry_ptr(const struct oidmap *map, + const struct object_id *key) +{ + struct oidmap_entry **e = &map->table[bucket(map, key)]; + while (*e && oidcmp(&(*e)->oid, key)) + e = &(*e)->next; + return e; +} + +void oidmap_init(struct oidmap *map, size_t initial_size) +{ + unsigned int size = OIDMAP_INITIAL_SIZE; + + memset(map, 0, sizeof(*map)); + + /* calculate initial table size and allocate the table */ + initial_size = (unsigned int) ((uint64_t) initial_size * 100 + / OIDMAP_LOAD_FACTOR); + while (initial_size > size) + size <<= OIDMAP_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 oidmap_free(struct oidmap *map, int free_entries) +{ + if (!map || !map->table) + return; + if (free_entries) { + int i; + for (i = 0; i < map->tablesize; i++) { + struct oidmap_entry *e = map->table[i]; + while (e) { + struct oidmap_entry *next = e->next; + free(e); + e = next; + } + } + } + free(map->table); + memset(map, 0, sizeof(*map)); +} + +void *oidmap_get(const struct oidmap *map, const struct object_id *key) +{ + return *find_entry_ptr(map, key); +} + +static void oidmap_add(struct oidmap *map, struct oidmap_entry *entry) +{ + unsigned int b = bucket(map, &entry->oid); + + /* add 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 << OIDMAP_RESIZE_BITS); + } +} + +void *oidmap_remove(struct oidmap *map, const struct object_id *key) +{ + struct oidmap_entry *old; + struct oidmap_entry **e = find_entry_ptr(map, key); + 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 >> OIDMAP_RESIZE_BITS); + } + + return old; +} + +void *oidmap_put(struct oidmap *map, void *entry) +{ + struct oidmap_entry *to_put = entry; + struct oidmap_entry *old = oidmap_remove(map, &to_put->oid); + oidmap_add(map, to_put); + return old; +} diff --git a/oidmap.h b/oidmap.h new file mode 100644 index 000000000..a543ed828 --- /dev/null +++ b/oidmap.h @@ -0,0 +1,98 @@ +#ifndef OIDMAP_H +#define OIDMAP_H + +/* + * struct oidmap_entry is a structure representing an entry in the hash table, + * which must be used as first member of user data structures. It must be + * zero-initialized (or use OIDMAP_ENTRY_INIT). + */ +struct oidmap_entry { + /* + * next points to the next entry in case of collisions (i.e. if + * multiple entries map to the same bucket). For oidmap's internal use + * only. + */ + struct oidmap_entry *next; + + struct object_id oid; +}; +#define OIDMAP_ENTRY_INIT { NULL } + +/* + * struct oidmap is the hash table structure. Members can be used as follows, + * but should not be modified directly. + */ +struct oidmap { + struct oidmap_entry **table; + + /* total number of entries (0 means the hashmap is empty) */ + unsigned int private_size; /* use oidmap_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; +}; + +/* oidmap functions */ + +/* + * Initializes an oidmap structure. + * + * `map` is the oidmap to initialize. + * + * 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. + */ +extern void oidmap_init(struct oidmap *map, size_t initial_size); + +/* + * Frees an oidmap structure and allocated memory. + * + * If `free_entries` is true, each oidmap_entry in the map is freed as well + * using stdlibs free(). + */ +extern void oidmap_free(struct oidmap *map, int free_entries); + +/* + * Return the number of items in the map. + */ +static inline unsigned int oidmap_get_size(struct oidmap *map) +{ + if (map->do_count_items) + return map->private_size; + + BUG("oidmap_get_size: size not set"); + return 0; +} + +/* + * Returns the oidmap entry for the specified oid, or NULL if not found. + */ +extern void *oidmap_get(const struct oidmap *map, + const struct object_id *key); + +/* + * Adds or replaces an oidmap entry. + * + * Returns the replaced entry, or NULL if not found (i.e. the entry was added). + */ +extern void *oidmap_put(struct oidmap *map, void *entry); + +/* + * Removes an oidmap entry matching the specified oid. + * + * Returns the removed entry, or NULL if not found. + */ +extern void *oidmap_remove(struct oidmap *map, const struct object_id *key); + +#endif diff --git a/oidset.c b/oidset.c index a6a08ba52..6fe7036c4 100644 --- a/oidset.c +++ b/oidset.c @@ -1,50 +1,30 @@ #include "cache.h" #include "oidset.h" -struct oidset_entry { - struct hashmap_entry hash; - struct object_id oid; -}; - -static int oidset_hashcmp(const void *unused_cmp_data, - const void *va, const void *vb, - const void *vkey) -{ - const struct oidset_entry *a = va, *b = vb; - const struct object_id *key = vkey; - return oidcmp(&a->oid, key ? key : &b->oid); -} - int oidset_contains(const struct oidset *set, const struct object_id *oid) { - struct hashmap_entry key; - - if (!set->map.cmpfn) + if (!set->map.tablesize) return 0; - - hashmap_entry_init(&key, sha1hash(oid->hash)); - return !!hashmap_get(&set->map, &key, oid); + return !!oidmap_get(&set->map, oid); } int oidset_insert(struct oidset *set, const struct object_id *oid) { - struct oidset_entry *entry; - - if (!set->map.cmpfn) - hashmap_init(&set->map, oidset_hashcmp, NULL, 0); + struct oidmap_entry *entry; - if (oidset_contains(set, oid)) + if (!set->map.tablesize) + oidmap_init(&set->map, 0); + else if (oidset_contains(set, oid)) return 1; - entry = xmalloc(sizeof(*entry)); - hashmap_entry_init(&entry->hash, sha1hash(oid->hash)); + entry = xcalloc(1, sizeof(*entry)); oidcpy(&entry->oid, oid); - hashmap_add(&set->map, entry); + oidmap_put(&set->map, entry); return 0; } void oidset_clear(struct oidset *set) { - hashmap_free(&set->map, 1); + oidmap_free(&set->map, 1); } diff --git a/oidset.h b/oidset.h index b7eaab5b8..b1ec82bfc 100644 --- a/oidset.h +++ b/oidset.h @@ -1,6 +1,8 @@ #ifndef OIDSET_H #define OIDSET_H +#include "oidmap.h" + /** * This API is similar to sha1-array, in that it maintains a set of object ids * in a memory-efficient way. The major differences are: @@ -17,7 +19,7 @@ * A single oidset; should be zero-initialized (or use OIDSET_INIT). */ struct oidset { - struct hashmap map; + struct oidmap map; }; #define OIDSET_INIT { { NULL } } -- 2.14.2.822.g60be5d43e6-goog
