Commit Graph

3 Commits

Author SHA1 Message Date
Elijah Newren
6ccdfc2a20 strmap: enable faster clearing and reusing of strmaps
When strmaps are used heavily, such as is done by my new merge-ort
algorithm, and strmaps need to be cleared but then re-used (because of
e.g. picking multiple commits to cherry-pick, or due to a recursive
merge having several different merges while recursing), free-ing and
reallocating map->table repeatedly can add up in time, especially since
it will likely be reallocated to a much smaller size but the previous
merge provides a good guide to the right size to use for the next merge.

Introduce strmap_partial_clear() to take advantage of this type of
situation; it will act similar to strmap_clear() except that
map->table's entries are zeroed instead of map->table being free'd.
Making use of this function reduced the cost of
clear_or_reinit_internal_opts() by about 20% in mert-ort, and dropped
the overall runtime of my rebase testcase by just under 2%.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-11-04 17:09:49 -08:00
Elijah Newren
b70c82e6ed strmap: add more utility functions
This adds a number of additional convienence functions I want/need:
  * strmap_get_size()
  * strmap_empty()
  * strmap_remove()
  * strmap_for_each_entry()
  * strmap_get_entry()

I suspect the first four are self-explanatory.

strmap_get_entry() is similar to strmap_get() except that instead of just
returning the void* value that the string maps to, it returns the
strmap_entry that contains both the string and the void* value (or
NULL if the string isn't in the map).  This is helpful because it avoids
multiple lookups, e.g. in some cases a caller would need to call:
  * strmap_contains() to check that the map has an entry for the string
  * strmap_get() to get the void* value
  * <do some work to update the value>
  * strmap_put() to update/overwrite the value
If the void* pointer returned really is a pointer, then the last step is
unnecessary, but if the void* pointer is just cast to an integer then
strmap_put() will be needed.  In contrast, one can call strmap_get_entry()
and then:
  * check if the string was in the map by whether the pointer is NULL
  * access the value via entry->value
  * directly update entry->value
meaning that we can replace two or three hash table lookups with one.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-11-04 17:09:49 -08:00
Elijah Newren
ae20bf1ad9 strmap: new utility functions
Add strmap as a new struct and associated utility functions,
specifically for hashmaps that map strings to some value.  The API is
taken directly from Peff's proposal at
https://lore.kernel.org/git/20180906191203.GA26184@sigill.intra.peff.net/

Note that similar string-list, I have a strdup_strings setting.
However, unlike string-list, strmap_init() does not take a parameter for
this setting and instead automatically sets it to 1; callers who want to
control this detail need to instead call strmap_init_with_options().
(Future patches will add additional parameters to
strmap_init_with_options()).

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-11-02 12:15:50 -08:00