From eaf7d631ad4140d78f63fd056c1749573e23d36b 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.
---
 mvcc/watchable_store.go      |  2 +-
 mvcc/watchable_store_test.go | 57 +++++++++++++++++++++---------------
 2 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/mvcc/watchable_store.go b/mvcc/watchable_store.go
index 2d8545942..14bb14ce2 100644
--- a/mvcc/watchable_store.go
+++ b/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/mvcc/watchable_store_test.go b/mvcc/watchable_store_test.go
index 52e1b90c0..84a0b6620 100644
--- a/mvcc/watchable_store_test.go
+++ b/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(testKey, nil, rev-1)
+			w := newStore.NewWatchStream()
+			w.Watch(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