fix(stage): fix race condition with stages.

server/channelserver/handlers_stage.go

@@ -111,10 +111,20 @@ func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
 	if !s.userEnteredStage {
 		s.userEnteredStage = true
 
+		// Lock server to safely iterate over sessions map
+		// We need to copy the session list first to avoid holding the lock during packet building
+		s.server.Lock()
+		var sessionList []*Session
 		for _, session := range s.server.sessions {
 			if s == session {
 				continue
 			}
+			sessionList = append(sessionList, session)
+		}
+		s.server.Unlock()
+
+		// Build packets for each session without holding the lock
+		for _, session := range sessionList {
 			temp = &mhfpacket.MsgSysInsertUser{CharID: session.charID}
 			newNotif.WriteUint16(uint16(temp.Opcode()))
 			temp.Build(newNotif, s.clientContext)
@@ -132,12 +142,22 @@ func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
 	if s.stage != nil { // avoids lock up when using bed for dream quests
 		// Notify the client to duplicate the existing objects.
 		s.logger.Info(fmt.Sprintf("Sending existing stage objects to %s", s.Name))
+
+		// Lock stage to safely iterate over objects map
+		// We need to copy the objects list first to avoid holding the lock during packet building
 		s.stage.RLock()
-		var temp mhfpacket.MHFPacket
+		var objectList []*Object
 		for _, obj := range s.stage.objects {
 			if obj.ownerCharID == s.charID {
 				continue
 			}
+			objectList = append(objectList, obj)
+		}
+		s.stage.RUnlock()
+
+		// Build packets for each object without holding the lock
+		var temp mhfpacket.MHFPacket
+		for _, obj := range objectList {
 			temp = &mhfpacket.MsgSysDuplicateObject{
 				ObjID:       obj.id,
 				X:           obj.x,
@@ -149,7 +169,6 @@ func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
 			newNotif.WriteUint16(uint16(temp.Opcode()))
 			temp.Build(newNotif, s.clientContext)
 		}
-		s.stage.RUnlock()
 	}
 
 	// FIX: Always send stage transfer packet, even if empty.
@@ -166,7 +185,12 @@ func destructEmptyStages(s *Session) {
 	for _, stage := range s.server.stages {
 		// Destroy empty Quest/My series/Guild stages.
 		if stage.id[3:5] == "Qs" || stage.id[3:5] == "Ms" || stage.id[3:5] == "Gs" || stage.id[3:5] == "Ls" {
-			if len(stage.reservedClientSlots) == 0 && len(stage.clients) == 0 {
+			// Lock stage to safely check its client and reservation counts
+			stage.Lock()
+			isEmpty := len(stage.reservedClientSlots) == 0 && len(stage.clients) == 0
+			stage.Unlock()
+
+			if isEmpty {
 				delete(s.server.stages, stage.id)
 				s.logger.Debug("Destructed stage", zap.String("stage.id", stage.id))
 			}
@@ -183,6 +207,7 @@ func removeSessionFromStage(s *Session) {
 	delete(s.stage.clients, s)
 
 	// Collect objects to delete while holding lock
+	// We must copy the objects to delete to avoid modifying the map while iterating
 	s.logger.Info("Sending notification to old stage clients")
 	var objectsToDelete []*Object
 	for _, object := range s.stage.objects {
@@ -209,6 +234,30 @@ func removeSessionFromStage(s *Session) {
 	destructEmptySemaphores(s)
 }
 
+func isStageFull(s *Session, StageID string) bool {
+	s.server.Lock()
+	stage, exists := s.server.stages[StageID]
+	s.server.Unlock()
+
+	if exists {
+		// Lock stage to safely check client counts
+		// Read the values we need while holding RLock, then release immediately
+		// to avoid deadlock with other functions that might hold server lock
+		stage.RLock()
+		reserved := len(stage.reservedClientSlots)
+		clients := len(stage.clients)
+		_, hasReservation := stage.reservedClientSlots[s.charID]
+		maxPlayers := stage.maxPlayers
+		stage.RUnlock()
+
+		if hasReservation {
+			return false
+		}
+		return reserved+clients >= int(maxPlayers)
+	}
+	return false
+}
+
 func handleMsgSysEnterStage(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysEnterStage)