Fix: free s.Cron on proper opportunity to avoid unexpected crash.

dkron/agent.go

@@ -240,6 +240,7 @@ func (a *Agent) Stop() error {
 
 	if a.config.Server && a.sched.Started {
 		a.sched.Stop()
+		a.sched.ClearCron()
 	}
 
 	if err := a.serf.Leave(); err != nil {

dkron/scheduler.go

@@ -60,7 +60,10 @@ func (s *Scheduler) Stop() {
 		log.Debug("scheduler: Stopping scheduler")
 		s.Cron.Stop()
 		s.Started = false
-		s.Cron = nil
+		// Keep Cron exists and let the jobs which have been scheduled can continue to finish,
+		// even the node's leadership will be revoked.
+		// Ignore the running jobs and make s.Cron to nil may cause whole process crashed.
+		//s.Cron = nil
 
 		// expvars
 		cronInspect.Do(func(kv expvar.KeyValue) {
@@ -73,9 +76,15 @@ func (s *Scheduler) Stop() {
 // Restart the scheduler
 func (s *Scheduler) Restart(jobs []*Job, agent *Agent) {
 	s.Stop()
+	s.ClearCron()
 	s.Start(jobs, agent)
 }
 
+// Clear cron separately, this can only be called when agent will be stop.
+func (s *Scheduler) ClearCron() {
+	s.Cron = nil
+}
+
 // GetEntry returns a scheduler entry from a snapshot in
 // the current time, and whether or not the entry was found.
 func (s *Scheduler) GetEntry(jobName string) (cron.Entry, bool) {