index-pack: restore "resolving deltas" progress meter

Commit f08cbf60fe (index-pack: make quantum of work smaller, 2020-09-08)
refactored the main loop in threaded_second_pass(), but also deleted the
call to display_progress() at the top of the loop. This means that users
typically see no progress at all during the delta resolution phase (and
for large repositories, Git appears to hang).

This looks like an accident that was unrelated to the intended change of
that commit, since we continue to update nr_resolved_deltas in
resolve_delta(). Let's restore the call to get that progress back.

We'll also add a test that confirms we generate the expected progress.
This isn't perfect, as it wouldn't catch a bug where progress was
delayed to the end. That was probably possible to trigger when receiving
a thin pack, because we'd eventually call display_progress() from
fix_unresolved_deltas(), but only once after doing all the work.
However, since our test case generates a complete pack, it reliably
demonstrates this particular bug and its fix. And we can't do better
without making the test racy.

Signed-off-by: Jeff King <peff@peff.net>
Acked-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 8da4031e72..0f05533902 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -1028,6 +1028,10 @@ static void *threaded_second_pass(void *data)
 		struct object_entry *child_obj;
 		struct base_data *child;
 
+		counter_lock();
+		display_progress(progress, nr_resolved_deltas);
+		counter_unlock();
+
 		work_lock();
 		if (list_empty(&work_head)) {
 			/*