Now that we have an efficient way to iterate, in order, over the
mmapped contents of the `packed-refs` file, we can use that directly
to implement reference iteration for the `packed_ref_store`, rather
than iterating over the `ref_cache`. This is the next step towards
getting rid of the `ref_cache` entirely.
Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
refs/packed-backend.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 106 insertions(+), 3 deletions(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 2a36dd9afb..a018a6c8ad 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -372,6 +372,27 @@ static int cmp_packed_ref_entries(const void *v1, const
void *v2)
}
}
+/*
+ * Compare a packed-refs record pointed to by `rec` to the specified
+ * NUL-terminated refname.
+ */
+static int cmp_entry_to_refname(const char *rec, const char *refname)
+{
+ const char *r1 = rec + GIT_SHA1_HEXSZ + 1;
+ const char *r2 = refname;
+
+ while (1) {
+ if (*r1 == '\n')
+ return *r2 ? -1 : 0;
+ if (!*r2)
+ return 1;
+ if (*r1 != *r2)
+ return (unsigned char)*r1 < (unsigned char)*r2 ? -1 :
+1;
+ r1++;
+ r2++;
+ }
+}
+
/*
* `packed_refs->buf` is not known to be sorted. Check whether it is,
* and if not, sort it into new memory and munmap/free the old
@@ -478,6 +499,17 @@ static const char *find_start_of_record(const char *buf,
const char *p)
return p;
}
+/*
+ * Return a pointer to the start of the record following the record
+ * that contains `*p`. If none is found before `end`, return `end`.
+ */
+static const char *find_end_of_record(const char *p, const char *end)
+{
+ while (++p < end && (p[-1] != '\n' || p[0] == '^'))
+ ;
+ return p;
+}
+
/*
* We want to be able to compare mmapped reference records quickly,
* without totally parsing them. We can do so because the records are
@@ -511,6 +543,65 @@ static void verify_buffer_safe(struct packed_ref_cache
*packed_refs)
last_line, eof - last_line);
}
+/*
+ * Find the place in `cache->buf` where the start of the record for
+ * `refname` starts. If `mustexist` is true and the reference doesn't
+ * exist, then return NULL. If `mustexist` is false and the reference
+ * doesn't exist, then return the point where that reference would be
+ * inserted. In the latter mode, `refname` doesn't have to be a proper
+ * reference name; for example, one could search for "refs/replace/"
+ * to find the start of any replace references.
+ *
+ * The record is sought using a binary search, so `cache->buf` must be
+ * sorted.
+ */
+static const char *find_reference_location(struct packed_ref_cache *cache,
+ const char *refname, int mustexist)
+{
+ /*
+ * This is not *quite* a garden-variety binary search, because
+ * the data we're searching is made up of records, and we
+ * always need to find the beginning of a record to do a
+ * comparison. A "record" here is one line for the reference
+ * itself and zero or one peel lines that start with '^'. Our
+ * loop invariant is described in the next two comments.
+ */
+
+ /*
+ * A pointer to the character at the start of a record whose
+ * preceding records all have reference names that come
+ * *before* `refname`.
+ */
+ const char *lo = cache->buf + cache->header_len;
+
+ /*
+ * A pointer to a the first character of a record whose
+ * reference name comes *after* `refname`.
+ */
+ const char *hi = cache->eof;
+
+ while (lo < hi) {
+ const char *mid, *rec;
+ int cmp;
+
+ mid = lo + (hi - lo) / 2;
+ rec = find_start_of_record(lo, mid);
+ cmp = cmp_entry_to_refname(rec, refname);
+ if (cmp < 0) {
+ lo = find_end_of_record(mid, hi);
+ } else if (cmp > 0) {
+ hi = rec;
+ } else {
+ return rec;
+ }
+ }
+
+ if (mustexist)
+ return NULL;
+ else
+ return lo;
+}
+
/*
* Read from the `packed-refs` file into a newly-allocated
* `packed_ref_cache` and return it. The return value will already
@@ -818,6 +909,8 @@ static struct ref_iterator *packed_ref_iterator_begin(
const char *prefix, unsigned int flags)
{
struct packed_ref_store *refs;
+ struct packed_ref_cache *packed_refs;
+ const char *start;
struct packed_ref_iterator *iter;
struct ref_iterator *ref_iterator;
unsigned int required_flags = REF_STORE_READ;
@@ -835,13 +928,23 @@ static struct ref_iterator *packed_ref_iterator_begin(
* the packed-ref cache is up to date with what is on disk,
* and re-reads it if not.
*/
+ iter->cache = packed_refs = get_packed_ref_cache(refs);
+ acquire_packed_ref_cache(packed_refs);
- iter->cache = get_packed_ref_cache(refs);
- acquire_packed_ref_cache(iter->cache);
- iter->iter0 = cache_ref_iterator_begin(iter->cache->cache, prefix, 0);
+ if (prefix && *prefix)
+ start = find_reference_location(packed_refs, prefix, 0);
+ else
+ start = packed_refs->buf + packed_refs->header_len;
+
+ iter->iter0 = mmapped_ref_iterator_begin(
+ packed_refs, start, packed_refs->eof);
iter->flags = flags;
+ if (prefix && *prefix)
+ /* Stop iteration after we've gone *past* prefix: */
+ ref_iterator = prefix_ref_iterator_begin(ref_iterator, prefix,
0);
+
return ref_iterator;
}
--
2.14.1
