cluster: speed scheduler exit (#4148) (#4198)

* This is an automated cherry-pick of #4148

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

server/cluster/cluster.go

@@ -359,8 +359,8 @@ 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

@@ -775,6 +775,12 @@ 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()