get_packed_ref_cache(): assume "packed-refs" won't change while locked

If we've got the "packed-refs" file locked, then it can't change;
there's no need to keep calling `stat_validity_check()` on it.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 2951439..c4bc955 100644 (file)
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -342,13 +342,18 @@ static void files_ref_path(struct files_ref_store *refs,
 
 /*
  * Get the packed_ref_cache for the specified files_ref_store,
- * creating it if necessary.
+ * creating and populating it if it hasn't been read before or if the
+ * file has been changed (according to its `validity` field) since it
+ * was last read. On the other hand, if we hold the lock, then assume
+ * that the file hasn't been changed out from under us, so skip the
+ * extra `stat()` call in `stat_validity_check()`.
  */
 static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *refs)
 {
        const char *packed_refs_file = files_packed_refs_path(refs);
 
        if (refs->packed &&
+           !is_lock_file_locked(&refs->packed_refs_lock) &&
            !stat_validity_check(&refs->packed->validity, packed_refs_file))
                clear_packed_ref_cache(refs);
 
@@ -1288,10 +1293,11 @@ static int lock_packed_refs(struct files_ref_store *refs, int flags)
                            flags, timeout_value) < 0)
                return -1;
        /*
-        * Get the current packed-refs while holding the lock.  If the
-        * packed-refs file has been modified since we last read it,
-        * this will automatically invalidate the cache and re-read
-        * the packed-refs file.
+        * Get the current packed-refs while holding the lock. It is
+        * important that we call `get_packed_ref_cache()` before
+        * setting `packed_ref_cache->lock`, because otherwise the
+        * former will see that the file is locked and assume that the
+        * cache can't be stale.
         */
        packed_ref_cache = get_packed_ref_cache(refs);
        /* Increment the reference count to prevent it from being freed: */