Fix events timeout errors

Resetting the timeout doesn't fully cut it, as it may timeout after we
got an event and be delivered later. This should fix it well enough for
the moment. https://github.com/golang/go/issues/11513

lib/events/events.go

@@ -188,12 +188,19 @@ func (s *Subscription) Poll(timeout time.Duration) (Event, error) {
 		dl.Debugln("poll", timeout)
 	}
 
-	s.timeout.Reset(timeout)
+	if !s.timeout.Reset(timeout) {
+		select {
+		case <-s.timeout.C:
+		default:
+		}
+	}
+
 	select {
 	case e, ok := <-s.events:
 		if !ok {
 			return e, ErrClosed
 		}
+		s.timeout.Stop()
 		return e, nil
 	case <-s.timeout.C:
 		return Event{}, ErrTimeout

lib/events/events_test.go

@@ -14,7 +14,7 @@ import (
 	"github.com/syncthing/syncthing/lib/events"
 )
 
-const timeout = 500 * time.Millisecond
+const timeout = 100 * time.Millisecond
 
 func TestNewLogger(t *testing.T) {
 	l := events.NewLogger()
@@ -26,6 +26,7 @@ func TestNewLogger(t *testing.T) {
 func TestSubscriber(t *testing.T) {
 	l := events.NewLogger()
 	s := l.Subscribe(0)
+	defer l.Unsubscribe(s)
 	if s == nil {
 		t.Fatal("Unexpected nil Subscription")
 	}
@@ -34,6 +35,7 @@ func TestSubscriber(t *testing.T) {
 func TestTimeout(t *testing.T) {
 	l := events.NewLogger()
 	s := l.Subscribe(0)
+	defer l.Unsubscribe(s)
 	_, err := s.Poll(timeout)
 	if err != events.ErrTimeout {
 		t.Fatal("Unexpected non-Timeout error:", err)
@@ -45,6 +47,7 @@ func TestEventBeforeSubscribe(t *testing.T) {
 
 	l.Log(events.DeviceConnected, "foo")
 	s := l.Subscribe(0)
+	defer l.Unsubscribe(s)
 
 	_, err := s.Poll(timeout)
 	if err != events.ErrTimeout {
@@ -56,6 +59,7 @@ func TestEventAfterSubscribe(t *testing.T) {
 	l := events.NewLogger()
 
 	s := l.Subscribe(events.AllEvents)
+	defer l.Unsubscribe(s)
 	l.Log(events.DeviceConnected, "foo")
 
 	ev, err := s.Poll(timeout)
@@ -80,6 +84,7 @@ func TestEventAfterSubscribeIgnoreMask(t *testing.T) {
 	l := events.NewLogger()
 
 	s := l.Subscribe(events.DeviceDisconnected)
+	defer l.Unsubscribe(s)
 	l.Log(events.DeviceConnected, "foo")
 
 	_, err := s.Poll(timeout)
@@ -91,7 +96,8 @@ func TestEventAfterSubscribeIgnoreMask(t *testing.T) {
 func TestBufferOverflow(t *testing.T) {
 	l := events.NewLogger()
 
-	_ = l.Subscribe(events.AllEvents)
+	s := l.Subscribe(events.AllEvents)
+	defer l.Unsubscribe(s)
 
 	t0 := time.Now()
 	for i := 0; i < events.BufferSize*2; i++ {
@@ -126,6 +132,7 @@ func TestIDs(t *testing.T) {
 	l := events.NewLogger()
 
 	s := l.Subscribe(events.AllEvents)
+	defer l.Unsubscribe(s)
 	l.Log(events.DeviceConnected, "foo")
 	l.Log(events.DeviceConnected, "bar")
 
@@ -154,6 +161,7 @@ func TestBufferedSub(t *testing.T) {
 	l := events.NewLogger()
 
 	s := l.Subscribe(events.AllEvents)
+	defer l.Unsubscribe(s)
 	bs := events.NewBufferedSubscription(s, 10*events.BufferSize)
 
 	go func() {