[PATCH v3 04/13] hashmap: introduce a new hashmap_partial_clear()
- From
Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>
- Date
- Nov 2, 2020, 18:55 UTC
- Message-ID
- <61f1da3c51b521035ba728c025cd6a28397f8051.1604343314.git.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.835.v3.git.git.1604343313.gitgitgadget@gmail.com>
From: Elijah Newren <newren@gmail.com>
merge-ort is a heavy user of strmaps, which are built on hashmap.[ch]. clear_or_reinit_internal_opts() in merge-ort was taking about 12% of overall runtime in my testcase involving rebasing 35 patches of linux.git across a big rename. clear_or_reinit_internal_opts() was calling hashmap_free() followed by hashmap_init(), meaning that not only was it freeing all the memory associated with each of the strmaps just to immediately allocate a new array again, it was allocating a new array that was likely smaller than needed (thus resulting in later need to rehash things). The ending size of the map table on the previous commit was likely almost perfectly sized for the next commit we wanted to pick, and not dropping and reallocating the table immediately is a win.
Add some new API to hashmap to clear a hashmap of entries without freeing map->table (and instead only zeroing it out like alloc_table() would do, along with zeroing the count of items in the table and the shrink_at field).
Signed-off-by: Elijah Newren <newren@gmail.com> --- hashmap.c | 39 +++++++++++++++++++++++++++------------ hashmap.h | 13 ++++++++++++- 2 files changed, 39 insertions(+), 13 deletions(-)
diff --git a/hashmap.c b/hashmap.c index bb7c9979b8..922ed07954 100644 --- a/hashmap.c +++ b/hashmap.c @@ -174,22 +174,37 @@ void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function, map->do_count_items = 1; } +static void free_individual_entries(struct hashmap *map, ssize_t entry_offset) +{ + struct hashmap_iter iter; + struct hashmap_entry *e; + + hashmap_iter_init(map, &iter); + while ((e = hashmap_iter_next(&iter))) + /* + * like container_of, but using caller-calculated + * offset (caller being hashmap_free_entries) + */ + free((char *)e - entry_offset); +} + +void hashmap_partial_clear_(struct hashmap *map, ssize_t entry_offset) +{ + if (!map || !map->table) + return; + if (entry_offset >= 0) /* called by hashmap_clear_entries */ + free_individual_entries(map, entry_offset); + memset(map->table, 0, map->tablesize * sizeof(struct hashmap_entry *)); + map->shrink_at = 0; + map->private_size = 0; +} + void hashmap_free_(struct hashmap *map, ssize_t entry_offset) { if (!map || !map->table) return; - if (entry_offset >= 0) { /* called by hashmap_free_entries */ - struct hashmap_iter iter; - struct hashmap_entry *e; - - hashmap_iter_init(map, &iter); - while ((e = hashmap_iter_next(&iter))) - /* - * like container_of, but using caller-calculated - * offset (caller being hashmap_free_entries) - */ - free((char *)e - entry_offset); - } + if (entry_offset >= 0) /* called by hashmap_free_entries */ + free_individual_entries(map, entry_offset); free(map->table); memset(map, 0, sizeof(*map)); } diff --git a/hashmap.h b/hashmap.h index 3b0f2bcade..e9430d582a 100644 --- a/hashmap.h +++ b/hashmap.h @@ -235,7 +235,8 @@ void hashmap_init(struct hashmap *map, const void *equals_function_data, size_t initial_size); -/* internal function for freeing hashmap */ +/* internal functions for clearing or freeing hashmap */ +void hashmap_partial_clear_(struct hashmap *map, ssize_t offset); void hashmap_free_(struct hashmap *map, ssize_t offset); /* @@ -268,6 +269,16 @@ void hashmap_free_(struct hashmap *map, ssize_t offset); */ #define hashmap_free(map) hashmap_free_(map, -1) +/* + * Basically the same as calling hashmap_free() followed by hashmap_init(), + * but doesn't incur the overhead of deallocating and reallocating + * map->table; it leaves map->table allocated and the same size but zeroes + * it out so it's ready for use again as an empty map. As with + * hashmap_free(), you may need to free the entries yourself before calling + * this function. + */ +#define hashmap_partial_clear(map) hashmap_partial_clear_(map, -1) + /* * Frees @map and all entries. @type is the struct type of the entry * where @member is the hashmap_entry struct used to associate with @map.
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