cluster: speed scheduler exit (#4148) (#4199)

* This is an automated cherry-pick of #4148

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

* resolv conflict

Signed-off-by: bufferflies <1045931706@qq.com>

Co-authored-by: buffer <1045931706@qq.com>

server/cluster/cluster.go

@@ -383,8 +383,8 @@ func (c *RaftCluster) Stop() {
 	}
 
 	c.running = false
-	close(c.quit)
 	c.coordinator.stop()
+	close(c.quit)
 	c.Unlock()
 	c.wg.Wait()
 	log.Info("raftcluster is stopped")

server/cluster/coordinator.go

@@ -822,6 +822,12 @@ func (s *scheduleController) Stop() {
 
 func (s *scheduleController) Schedule() []*operator.Operator {
 	for i := 0; i < maxScheduleRetries; i++ {
+		// no need to retry if schedule should stop to speed exit
+		select {
+		case <-s.ctx.Done():
+			return nil
+		default:
+		}
 		// If we have schedule, reset interval to the minimal interval.
 		if op := s.Scheduler.Schedule(s.cluster); op != nil {
 			s.nextInterval = s.Scheduler.GetMinInterval()