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rerere: use strmap to store rerere directories

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We store a struct for each directory we access under .git/rr-cache. The
structs are kept in an array sorted by the binary hash associated with
their name (and we do lookups with a binary search).

This works OK, but there are a few small downsides:

 - the amount of code isn't huge, but it's more than we'd need using one
   of our other stock data structures

 - the insertion into a sorted array is quadratic (though in practice
   it's unlikely anybody has enough conflicts for this to matter)

 - it's intimately tied to the representation of an object hash. This
   isn't a big deal, as the conflict ids we generate use the same hash,
   but it produces a few awkward bits (e.g., we are the only user of
   hash_pos() that is not using object_id).

Let's instead just treat the directory names as strings, and store them
in a strmap. This is less code, and removes the use of hash_pos().

Insertion is now non-quadratic, though we probably use a bit more
memory. Besides the hash table overhead, and storing hex bytes instead
of a binary hash, we actually store each name twice. Other code expects
to access the name of a rerere_dir struct from the struct itself, so we
need a copy there. But strmap keeps its own copy of the name, as well.

Using a bare hashmap instead of strmap means we could use the name for
both, but at the cost of extra code (e.g., our own comparison function).
Likewise, strmap has a feature to use a pointer to the in-struct name at
the cost of a little extra code. I didn't do either here, as simple code
seemed more important than squeezing out a few bytes of efficiency.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2021-01-28 01:34:31 -05:00 committed by Junio C Hamano
parent 098c173f2b
commit 680ff910b0
1 changed files with 21 additions and 37 deletions
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58
rerere.c
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@ -11,6 +11,7 @@
#include "pathspec.h"
#include "object-store.h"
#include "hash-lookup.h"
#include "strmap.h"
#define RESOLVED 0
#define PUNTED 1
@ -23,26 +24,27 @@ static int rerere_enabled = -1;
/* automatically update cleanly resolved paths to the index */
static int rerere_autoupdate;
static int rerere_dir_nr;
static int rerere_dir_alloc;
#define RR_HAS_POSTIMAGE 1
#define RR_HAS_PREIMAGE 2
static struct rerere_dir {
unsigned char hash[GIT_MAX_HEXSZ];
struct rerere_dir {
int status_alloc, status_nr;
unsigned char *status;
} **rerere_dir;
char name[FLEX_ARRAY];
};
static struct strmap rerere_dirs = STRMAP_INIT;
static void free_rerere_dirs(void)
{
int i;
for (i = 0; i < rerere_dir_nr; i++) {
free(rerere_dir[i]->status);
free(rerere_dir[i]);
struct hashmap_iter iter;
struct strmap_entry *ent;
strmap_for_each_entry(&rerere_dirs, &iter, ent) {
struct rerere_dir *rr_dir = ent->value;
free(rr_dir->status);
free(rr_dir);
}
FREE_AND_NULL(rerere_dir);
rerere_dir_nr = rerere_dir_alloc = 0;
strmap_clear(&rerere_dirs, 0);
}
static void free_rerere_id(struct string_list_item *item)
@ -52,7 +54,7 @@ static void free_rerere_id(struct string_list_item *item)
static const char *rerere_id_hex(const struct rerere_id *id)
{
return hash_to_hex(id->collection->hash);
return id->collection->name;
}
static void fit_variant(struct rerere_dir *rr_dir, int variant)
@ -115,7 +117,7 @@ static int is_rr_file(const char *name, const char *filename, int *variant)
static void scan_rerere_dir(struct rerere_dir *rr_dir)
{
struct dirent *de;
DIR *dir = opendir(git_path("rr-cache/%s", hash_to_hex(rr_dir->hash)));
DIR *dir = opendir(git_path("rr-cache/%s", rr_dir->name));
if (!dir)
return;
@ -133,39 +135,21 @@ static void scan_rerere_dir(struct rerere_dir *rr_dir)
closedir(dir);
}
static const unsigned char *rerere_dir_hash(size_t i, void *table)
{
struct rerere_dir **rr_dir = table;
return rr_dir[i]->hash;
}
static struct rerere_dir *find_rerere_dir(const char *hex)
{
unsigned char hash[GIT_MAX_RAWSZ];
struct rerere_dir *rr_dir;
int pos;
if (get_sha1_hex(hex, hash))
BUG("cannot parse rerere dir hex?");
pos = hash_pos(hash, rerere_dir, rerere_dir_nr, rerere_dir_hash);
if (pos < 0) {
rr_dir = xmalloc(sizeof(*rr_dir));
hashcpy(rr_dir->hash, hash);
rr_dir = strmap_get(&rerere_dirs, hex);
if (!rr_dir) {
FLEX_ALLOC_STR(rr_dir, name, hex);
rr_dir->status = NULL;
rr_dir->status_nr = 0;
rr_dir->status_alloc = 0;
pos = -1 - pos;
strmap_put(&rerere_dirs, hex, rr_dir);
/* Make sure the array is big enough ... */
ALLOC_GROW(rerere_dir, rerere_dir_nr + 1, rerere_dir_alloc);
/* ... and add it in. */
rerere_dir_nr++;
MOVE_ARRAY(rerere_dir + pos + 1, rerere_dir + pos,
rerere_dir_nr - pos - 1);
rerere_dir[pos] = rr_dir;
scan_rerere_dir(rr_dir);
}
return rerere_dir[pos];
return rr_dir;
}
static int has_rerere_resolution(const struct rerere_id *id)