MM-10502: Only cluster master should run job schedulers. (#9174)

* MM-10502: Only cluster master should run job schedulers.

* Use sync.Map for thread safety.

* Fix tests.

jobs/schedulers.go

@@ -13,12 +13,13 @@ import (
 )
 
 type Schedulers struct {
-	stop          chan bool
-	stopped       chan bool
-	configChanged chan *model.Config
-	listenerId    string
-	startOnce     sync.Once
-	jobs          *JobServer
+	stop                 chan bool
+	stopped              chan bool
+	configChanged        chan *model.Config
+	clusterLeaderChanged chan bool
+	listenerId           string
+	startOnce            sync.Once
+	jobs                 *JobServer
 
 	schedulers   []model.Scheduler
 	nextRunTimes []*time.Time
@@ -28,10 +29,11 @@ func (srv *JobServer) InitSchedulers() *Schedulers {
 	mlog.Debug("Initialising schedulers.")
 
 	schedulers := &Schedulers{
-		stop:          make(chan bool),
-		stopped:       make(chan bool),
-		configChanged: make(chan *model.Config),
-		jobs:          srv,
+		stop:                 make(chan bool),
+		stopped:              make(chan bool),
+		configChanged:        make(chan *model.Config),
+		clusterLeaderChanged: make(chan bool),
+		jobs:                 srv,
 	}
 
 	if srv.DataRetentionJob != nil {
@@ -114,6 +116,14 @@ func (schedulers *Schedulers) Start() *Schedulers {
 							schedulers.setNextRunTime(newCfg, idx, now, false)
 						}
 					}
+				case isLeader := <-schedulers.clusterLeaderChanged:
+					for idx := range schedulers.schedulers {
+						if !isLeader {
+							schedulers.nextRunTimes[idx] = nil
+						} else {
+							schedulers.setNextRunTime(schedulers.jobs.Config(), idx, now, false)
+						}
+					}
 				}
 			}
 		})
@@ -171,3 +181,11 @@ func (schedulers *Schedulers) handleConfigChange(oldConfig *model.Config, newCon
 	mlog.Debug("Schedulers received config change.")
 	schedulers.configChanged <- newConfig
 }
+
+func (schedulers *Schedulers) HandleClusterLeaderChange(isLeader bool) {
+	select {
+	case schedulers.clusterLeaderChanged <- isLeader:
+	default:
+		mlog.Debug("Did not send cluster leader change message to schedulers as no schedulers listening to notification channel.")
+	}
+}

jobs/server.go

@@ -50,11 +50,11 @@ func (srv *JobServer) Config() *model.Config {
 }
 
 func (srv *JobServer) StartWorkers() {
-	srv.Workers = srv.InitWorkers().Start()
+	srv.Workers = srv.Workers.Start()
 }
 
 func (srv *JobServer) StartSchedulers() {
-	srv.Schedulers = srv.InitSchedulers().Start()
+	srv.Schedulers = srv.Schedulers.Start()
 }
 
 func (srv *JobServer) StopWorkers() {