[PATCH 4/4] refs.c: sort the refs by new_sha1 and merge the two update/delete loops into one

[Ronnie Sahlberg <sahlberg@google.com>]

We want to make sure that we update all refs before we delete any refs
so that there is no point in time where the tips may not be reachable
from any ref in the system.
We currently acheive this by first looping over all updates and applying
them before we run a second loop and perform all the deletes.

If we sort the new sha1 for all the refs so that a deleted ref,
with sha1 0{40} comes at the end of the array, then we can just run
a single loop and still guarantee that all updates happen before
any deletes.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/refs.c b/refs.c
index 1678e12..453318e 100644
--- a/refs.c
+++ b/refs.c
@@ -3309,6 +3309,15 @@ static int ref_update_compare(const void *r1, const void *r2)
 	return strcmp((*u1)->ref_name, (*u2)->ref_name);
 }
 
+static int ref_delete_compare(const void *r1, const void *r2)
+{
+	const struct ref_update * const *u1 = r1;
+	const struct ref_update * const *u2 = r2;
+
+	/* -strcmp so that 0{40} sorts to the end */
+	return -strcmp((*u1)->new_sha1, (*u2)->new_sha1);
+}
+
 static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 					enum action_on_err onerr)
 {
@@ -3388,13 +3397,8 @@ int update_refs(const char *action, const struct ref_update **updates_orig,
 		unlink_or_warn(git_path("logs/%s", delnames[i]));
 	clear_loose_ref_cache(&ref_cache);
 
-	/* Perform updates first so live commits remain referenced */
-	for (i = 0; i < n; i++)
-		if (locks[i] && !locks[i]->delete_ref) {
-			ret |= commit_ref_lock(locks[i]);
-			locks[i] = NULL;
-		}
-	/* And finally perform all deletes */
+	/* Sort the array so that we perform all updates before any deletes */
+	qsort(updates, n, sizeof(*updates), ref_delete_compare);
 	for (i = 0; i < n; i++)
 		if (locks[i]) {
 			ret |= commit_ref_lock(locks[i]);
-- 
1.9.1.478.ga5a8238.dirty