From fcab10bb2daf57cd3f5e985acce4df5042519103 Mon Sep 17 00:00:00 2001
From: Iwasaki Yudai <yudai.iwasaki@ntti3.com>
Date: Mon, 5 Feb 2018 17:08:24 -0800
Subject: [PATCH] mvcc: restore unsynced watchers

In case syncWatchersLoop() starts before Restore() is called,
watchers already added by that moment are moved to s.synced by the loop.
However, there is a broken logic that moves watchers from s.synced
to s.uncyned without setting keyWatchers of the watcherGroup.
Eventually syncWatchers() fails to pickup those watchers from s.unsynced
and no events are sent to the watchers, because newWatcherBatch() called
in the function uses wg.watcherSetByKey() internally that requires
a proper keyWatchers value.
---
 internal/mvcc/watchable_store.go      |  2 +-
 internal/mvcc/watchable_store_test.go | 57 ++++++++++++++++-----------
 2 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/internal/mvcc/watchable_store.go b/internal/mvcc/watchable_store.go
index 34d4d3265..054be1034 100644
--- a/internal/mvcc/watchable_store.go
+++ b/internal/mvcc/watchable_store.go
@@ -192,7 +192,7 @@ func (s *watchableStore) Restore(b backend.Backend) error {
 	}
 
 	for wa := range s.synced.watchers {
-		s.unsynced.watchers.add(wa)
+		s.unsynced.add(wa)
 	}
 	s.synced = newWatcherGroup()
 	return nil
diff --git a/internal/mvcc/watchable_store_test.go b/internal/mvcc/watchable_store_test.go
index aa0e29954..4f21aee45 100644
--- a/internal/mvcc/watchable_store_test.go
+++ b/internal/mvcc/watchable_store_test.go
@@ -297,36 +297,45 @@ func TestWatchFutureRev(t *testing.T) {
 }
 
 func TestWatchRestore(t *testing.T) {
-	b, tmpPath := backend.NewDefaultTmpBackend()
-	s := newWatchableStore(b, &lease.FakeLessor{}, nil)
-	defer cleanup(s, b, tmpPath)
+	test := func(delay time.Duration) func(t *testing.T) {
+		return func(t *testing.T) {
+			b, tmpPath := backend.NewDefaultTmpBackend()
+			s := newWatchableStore(b, &lease.FakeLessor{}, nil)
+			defer cleanup(s, b, tmpPath)
 
-	testKey := []byte("foo")
-	testValue := []byte("bar")
-	rev := s.Put(testKey, testValue, lease.NoLease)
+			testKey := []byte("foo")
+			testValue := []byte("bar")
+			rev := s.Put(testKey, testValue, lease.NoLease)
 
-	newBackend, newPath := backend.NewDefaultTmpBackend()
-	newStore := newWatchableStore(newBackend, &lease.FakeLessor{}, nil)
-	defer cleanup(newStore, newBackend, newPath)
+			newBackend, newPath := backend.NewDefaultTmpBackend()
+			newStore := newWatchableStore(newBackend, &lease.FakeLessor{}, nil)
+			defer cleanup(newStore, newBackend, newPath)
 
-	w := newStore.NewWatchStream()
-	w.Watch(0, testKey, nil, rev-1)
+			w := newStore.NewWatchStream()
+			w.Watch(0, testKey, nil, rev-1)
 
-	newStore.Restore(b)
-	select {
-	case resp := <-w.Chan():
-		if resp.Revision != rev {
-			t.Fatalf("rev = %d, want %d", resp.Revision, rev)
+			time.Sleep(delay)
+
+			newStore.Restore(b)
+			select {
+			case resp := <-w.Chan():
+				if resp.Revision != rev {
+					t.Fatalf("rev = %d, want %d", resp.Revision, rev)
+				}
+				if len(resp.Events) != 1 {
+					t.Fatalf("failed to get events from the response")
+				}
+				if resp.Events[0].Kv.ModRevision != rev {
+					t.Fatalf("kv.rev = %d, want %d", resp.Events[0].Kv.ModRevision, rev)
+				}
+			case <-time.After(time.Second):
+				t.Fatal("failed to receive event in 1 second.")
+			}
 		}
-		if len(resp.Events) != 1 {
-			t.Fatalf("failed to get events from the response")
-		}
-		if resp.Events[0].Kv.ModRevision != rev {
-			t.Fatalf("kv.rev = %d, want %d", resp.Events[0].Kv.ModRevision, rev)
-		}
-	case <-time.After(time.Second):
-		t.Fatal("failed to receive event in 1 second.")
 	}
+
+	t.Run("Normal", test(0))
+	t.Run("RunSyncWatchLoopBeforeRestore", test(time.Millisecond*120)) // longer than default waitDuration
 }
 
 // TestWatchBatchUnsynced tests batching on unsynced watchers