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pseudo-merge: implement support for reading pseudo-merge commits

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Implement the basic API for reading pseudo-merge bitmaps, which consists
of four basic functions:

  - pseudo_merge_bitmap()
  - use_pseudo_merge()
  - apply_pseudo_merges_for_commit()
  - cascade_pseudo_merges()

These functions are all documented in pseudo-merge.h, but their rough
descriptions are as follows:

  - pseudo_merge_bitmap() reads and inflates the objects EWAH bitmap for
    a given pseudo-merge

  - use_pseudo_merge() does the same as pseudo_merge_bitmap(), but on
    the commits EWAH bitmap, not the objects bitmap

  - apply_pseudo_merges_for_commit() applies all satisfied pseudo-merge
    commits for a given result set, and cascades any yet-unsatisfied
    pseudo-merges if any were applied in the previous step

  - cascade_pseudo_merges() applies all pseudo-merges which are
    satisfied but have not been previously applied, repeating this
    process until no more pseudo-merges can be applied

The core of the API is the latter two functions, which are responsible
for applying pseudo-merges during the object traversal implemented in
the pack-bitmap machinery.

The other two functions (pseudo_merge_bitmap(), and use_pseudo_merge())
are low-level ways to interact with the pseudo-merge machinery, which
will be useful in future commits.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
2024-05-23 17:26:58 -04:00
committed by Junio C Hamano
parent 7c0fae8844
commit 955747b4da
2 changed files with 279 additions and 0 deletions
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235
pseudo-merge.c
View File

@@ -10,6 +10,7 @@
#include "commit.h"
#include "alloc.h"
#include "progress.h"
#include "hex.h"
#define DEFAULT_PSEUDO_MERGE_DECAY 1.0
#define DEFAULT_PSEUDO_MERGE_MAX_MERGES 64
@@ -464,3 +465,237 @@ void free_pseudo_merge_map(struct pseudo_merge_map *pm)
}
free(pm->v);
}
struct pseudo_merge_commit_ext {
uint32_t nr;
const unsigned char *ptr;
};
static int pseudo_merge_ext_at(const struct pseudo_merge_map *pm,
struct pseudo_merge_commit_ext *ext, size_t at)
{
if (at >= pm->map_size)
return error(_("extended pseudo-merge read out-of-bounds "
"(%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)at, (uintmax_t)pm->map_size);
if (at + 4 >= pm->map_size)
return error(_("extended pseudo-merge entry is too short "
"(%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)(at + 4), (uintmax_t)pm->map_size);
ext->nr = get_be32(pm->map + at);
ext->ptr = pm->map + at + sizeof(uint32_t);
return 0;
}
struct ewah_bitmap *pseudo_merge_bitmap(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge)
{
if (!merge->loaded_commits)
BUG("cannot use unloaded pseudo-merge bitmap");
if (!merge->loaded_bitmap) {
size_t at = merge->bitmap_at;
merge->bitmap = read_bitmap(pm->map, pm->map_size, &at);
merge->loaded_bitmap = 1;
}
return merge->bitmap;
}
struct pseudo_merge *use_pseudo_merge(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge)
{
if (!merge->loaded_commits) {
size_t pos = merge->at;
merge->commits = read_bitmap(pm->map, pm->map_size, &pos);
merge->bitmap_at = pos;
merge->loaded_commits = 1;
}
return merge;
}
static struct pseudo_merge *pseudo_merge_at(const struct pseudo_merge_map *pm,
struct object_id *oid,
size_t want)
{
size_t lo = 0;
size_t hi = pm->nr;
while (lo < hi) {
size_t mi = lo + (hi - lo) / 2;
size_t got = pm->v[mi].at;
if (got == want)
return use_pseudo_merge(pm, &pm->v[mi]);
else if (got < want)
hi = mi;
else
lo = mi + 1;
}
warning(_("could not find pseudo-merge for commit %s at offset %"PRIuMAX),
oid_to_hex(oid), (uintmax_t)want);
return NULL;
}
struct pseudo_merge_commit {
uint32_t commit_pos;
uint64_t pseudo_merge_ofs;
};
#define PSEUDO_MERGE_COMMIT_RAWSZ (sizeof(uint32_t)+sizeof(uint64_t))
static void read_pseudo_merge_commit_at(struct pseudo_merge_commit *merge,
const unsigned char *at)
{
merge->commit_pos = get_be32(at);
merge->pseudo_merge_ofs = get_be64(at + sizeof(uint32_t));
}
static int nth_pseudo_merge_ext(const struct pseudo_merge_map *pm,
struct pseudo_merge_commit_ext *ext,
struct pseudo_merge_commit *merge,
uint32_t n)
{
size_t ofs;
if (n >= ext->nr)
return error(_("extended pseudo-merge lookup out-of-bounds "
"(%"PRIu32" >= %"PRIu32")"), n, ext->nr);
ofs = get_be64(ext->ptr + st_mult(n, sizeof(uint64_t)));
if (ofs >= pm->map_size)
return error(_("out-of-bounds read: (%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)ofs, (uintmax_t)pm->map_size);
read_pseudo_merge_commit_at(merge, pm->map + ofs);
return 0;
}
static unsigned apply_pseudo_merge(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge,
struct bitmap *result,
struct bitmap *roots)
{
if (merge->satisfied)
return 0;
if (!ewah_bitmap_is_subset(merge->commits, roots ? roots : result))
return 0;
bitmap_or_ewah(result, pseudo_merge_bitmap(pm, merge));
if (roots)
bitmap_or_ewah(roots, pseudo_merge_bitmap(pm, merge));
merge->satisfied = 1;
return 1;
}
static int pseudo_merge_commit_cmp(const void *va, const void *vb)
{
struct pseudo_merge_commit merge;
uint32_t key = *(uint32_t*)va;
read_pseudo_merge_commit_at(&merge, vb);
if (key < merge.commit_pos)
return -1;
if (key > merge.commit_pos)
return 1;
return 0;
}
static struct pseudo_merge_commit *find_pseudo_merge(const struct pseudo_merge_map *pm,
uint32_t pos)
{
if (!pm->commits_nr)
return NULL;
return bsearch(&pos, pm->commits, pm->commits_nr,
PSEUDO_MERGE_COMMIT_RAWSZ, pseudo_merge_commit_cmp);
}
int apply_pseudo_merges_for_commit(const struct pseudo_merge_map *pm,
struct bitmap *result,
struct commit *commit, uint32_t commit_pos)
{
struct pseudo_merge *merge;
struct pseudo_merge_commit *merge_commit;
int ret = 0;
merge_commit = find_pseudo_merge(pm, commit_pos);
if (!merge_commit)
return 0;
if (merge_commit->pseudo_merge_ofs & ((uint64_t)1<<63)) {
struct pseudo_merge_commit_ext ext = { 0 };
off_t ofs = merge_commit->pseudo_merge_ofs & ~((uint64_t)1<<63);
uint32_t i;
if (pseudo_merge_ext_at(pm, &ext, ofs) < -1) {
warning(_("could not read extended pseudo-merge table "
"for commit %s"),
oid_to_hex(&commit->object.oid));
return ret;
}
for (i = 0; i < ext.nr; i++) {
if (nth_pseudo_merge_ext(pm, &ext, merge_commit, i) < 0)
return ret;
merge = pseudo_merge_at(pm, &commit->object.oid,
merge_commit->pseudo_merge_ofs);
if (!merge)
return ret;
if (apply_pseudo_merge(pm, merge, result, NULL))
ret++;
}
} else {
merge = pseudo_merge_at(pm, &commit->object.oid,
merge_commit->pseudo_merge_ofs);
if (!merge)
return ret;
if (apply_pseudo_merge(pm, merge, result, NULL))
ret++;
}
if (ret)
cascade_pseudo_merges(pm, result, NULL);
return ret;
}
int cascade_pseudo_merges(const struct pseudo_merge_map *pm,
struct bitmap *result,
struct bitmap *roots)
{
unsigned any_satisfied;
int ret = 0;
do {
struct pseudo_merge *merge;
uint32_t i;
any_satisfied = 0;
for (i = 0; i < pm->nr; i++) {
merge = use_pseudo_merge(pm, &pm->v[i]);
if (apply_pseudo_merge(pm, merge, result, roots)) {
any_satisfied |= 1;
ret++;
}
}
} while (any_satisfied);
return ret;
}