Fix race condition on service stop

Jenkinsfile

@@ -1,2 +1,3 @@
 buildDebGolangWbgo defaultTargets: 'bullseye-armhf bullseye-arm64',
+                   defaultWbGoSoBranch: 'feature/amd64-build-race',
                    defaultRunLintian: true

Makefile

@@ -19,7 +19,7 @@ GOTEST ?= $(GO) test
 GCFLAGS :=
 LDFLAGS := -X main.version=`git describe --tags --always --dirty`
 GO_FLAGS := -buildvcs=false
-GO_TEST_FLAGS := -v -cover
+GO_TEST_FLAGS := -v -cover -race
 
 ifeq ($(DEBUG),)
 	LDFLAGS += -s -w

debian/changelog

@@ -1,3 +1,9 @@
+wb-rules (2.40.1) stable; urgency=medium
+
+  * Fix race condition on service stop
+
+ -- Nikolay Korotkiy <nikolay.korotkiy@wirenboard.com>  Wed, 13 May 2026 17:00:00 +0400
+
 wb-rules (2.40.0) stable; urgency=medium
 
   * Move notify/alarms to modules

wbrules/engine.go

@@ -628,6 +628,7 @@ type RuleEngine struct {
 	syncQueueActive bool
 	syncQueue       chan func()
 	syncQuitCh      chan chan struct{}
+	mainLoopDone    chan struct{}
 	mqttClient      wbgong.MQTTClient // for service
 	driver          wbgong.Driver
 	driverReadyCh   chan struct{}
@@ -689,6 +690,7 @@ func NewRuleEngine(driver wbgong.Driver, mqtt wbgong.MQTTClient, options *RuleEn
 		syncQueue:             make(chan func(), SYNC_QUEUE_LEN),
 		syncQueueActive:       true,
 		syncQuitCh:            make(chan chan struct{}, 1),
+		mainLoopDone:          nil,
 		mqttClient:            mqtt,
 		driver:                driver,
 		driverReadyCh:         nil,
@@ -983,6 +985,14 @@ func (engine *RuleEngine) driverEventHandler(event wbgong.DriverEvent) {
 }
 
 func (engine *RuleEngine) CallSync(thunk func()) {
+	engine.statusMtx.Lock()
+	syncQueueActive := engine.syncQueueActive
+	engine.statusMtx.Unlock()
+
+	if !syncQueueActive {
+		return
+	}
+
 	if atomic.LoadUint32(&engine.debugEnabled) == ATOMIC_TRUE {
 		delay := time.NewTimer(ENGINE_CALLSYNC_TIMEOUT)
 		select {
@@ -999,7 +1009,11 @@ func (engine *RuleEngine) CallSync(thunk func()) {
 }
 
 func (engine *RuleEngine) MaybeCallSync(thunk func()) {
-	if engine.syncQueueActive {
+	engine.statusMtx.Lock()
+	syncQueueActive := engine.syncQueueActive
+	engine.statusMtx.Unlock()
+
+	if syncQueueActive {
 		engine.CallSync(thunk)
 	} else {
 		thunk()
@@ -1281,6 +1295,11 @@ func (engine *RuleEngine) setupCron() {
 func (engine *RuleEngine) handleStop() {
 	wbgong.Debug.Printf("engine stopped")
 
+	if engine.cron != nil {
+		engine.cron.Stop()
+		engine.cron = nil
+	}
+
 	engine.timersMutex.Lock()
 	timerEntries := make([]*TimerEntry, 0, len(engine.timers))
 	for _, entry := range engine.timers {
@@ -1297,7 +1316,6 @@ func (engine *RuleEngine) handleStop() {
 	engine.readyCh = nil
 	engine.driverReadyCh = nil
 	engine.syncQueueActive = false
-	close(engine.syncQueue)
 	engine.statusMtx.Unlock()
 }
 
@@ -1339,18 +1357,25 @@ func (engine *RuleEngine) updateDebugEnabled() {
 }
 
 func (engine *RuleEngine) Start() {
+	engine.statusMtx.Lock()
 	engine.readyCh = make(chan struct{})
 	engine.driverReadyCh = make(chan struct{}, 1)
+	engine.syncQueueActive = true
+	engine.mainLoopDone = make(chan struct{})
+	engine.statusMtx.Unlock()
+
 	engine.eventBuffer = NewEventBuffer()
 
 	engine.driver.OnDriverEvent(engine.driverEventHandler)
 	engine.driver.OnRetainReady(func(tx wbgong.DriverTx) {
 		engine.driverReadyCh <- struct{}{}
 	})
-	engine.syncQueueActive = true
 	atomic.StoreUint32(&engine.active, ENGINE_ACTIVE)
 
-	go engine.mainLoop()
+	go func() {
+		defer close(engine.mainLoopDone)
+		engine.mainLoop()
+	}()
 	go engine.syncLoop()
 }
 
@@ -1365,13 +1390,18 @@ func (engine *RuleEngine) Stop() {
 
 	engine.eventBuffer.Close()
 
+	// wait for main loop shutdown sequence to finish
+	engine.statusMtx.Lock()
+	mainLoopDone := engine.mainLoopDone
+	engine.statusMtx.Unlock()
+	if mainLoopDone != nil {
+		<-mainLoopDone
+	}
+
 	// stop sync loop
 	q := make(chan struct{})
 	engine.syncQuitCh <- q
 	<-q
-
-	// wait for main loop to release sync queue
-	<-engine.syncQueue
 }
 
 func (engine *RuleEngine) IsActive() bool {