refs: do not invalidate the packed-refs cache unnecessarily

Now that we keep track of the packed-refs file metadata, we can detect
when the packed-refs file has been modified since we last read it, and
we do so automatically every time that get_packed_ref_cache() is
called.  So there is no need to invalidate the cache automatically
when lock_packed_refs() is called; usually the old copy will still be
valid.

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

diff --git a/refs.c b/refs.c
index 787cc1c9bc6af558bceb18d933321e93b399f195..038e5c72d74bd11020a929204d136ccb076d4dc1 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -2136,11 +2136,14 @@ int lock_packed_refs(int flags)
 {
        struct packed_ref_cache *packed_ref_cache;
 
-       /* Discard the old cache because it might be invalid: */
-       clear_packed_ref_cache(&ref_cache);
        if (hold_lock_file_for_update(&packlock, git_path("packed-refs"), flags) < 0)
                return -1;
-       /* Read the current packed-refs while holding the lock: */
+       /*
+        * 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.
+        */
        packed_ref_cache = get_packed_ref_cache(&ref_cache);
        packed_ref_cache->lock = &packlock;
        /* Increment the reference count to prevent it from being freed: */