From b6373f16255f88314a29932c58b0c143e4eeae77 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 028e05b9a..7be9641d4 100644
--- a/mvcc/watchable_store.go
+++ b/mvcc/watchable_store.go
@@ -267,7 +267,7 @@ 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 42d2ae571..25639fa8a 100644
--- a/mvcc/watchable_store_test.go
+++ b/mvcc/watchable_store_test.go
@@ -295,36 +295,45 @@ 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(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