Minor refactor to campaign manager.

- Remove external invocation of worker goroutines into Run()
- Split Run() into smaller functions.

internal/manager/manager.go

@@ -181,65 +181,19 @@ func (m *Manager) HasMessenger(id string) bool {
 	return ok
 }
 
-// Run is a blocking function (and hence should be invoked as a goroutine)
-// that scans the source db at regular intervals for pending campaigns,
+// Run is a blocking function (that should be invoked as a goroutine)
+// that scans the data source at regular intervals for pending campaigns,
 // and queues them for processing. The process queue fetches batches of
 // subscribers and pushes messages to them for each queued campaign
 // until all subscribers are exhausted, at which point, a campaign is marked
 // as "finished".
 func (m *Manager) Run(tick time.Duration) {
-	go func() {
-		t := time.NewTicker(tick)
-		for {
-			select {
-			// Periodically scan the data source for campaigns to process.
-			case <-t.C:
-				campaigns, err := m.src.NextCampaigns(m.getPendingCampaignIDs())
-				if err != nil {
-					m.logger.Printf("error fetching campaigns: %v", err)
-					continue
-				}
-
-				for _, c := range campaigns {
-					if err := m.addCampaign(c); err != nil {
-						m.logger.Printf("error processing campaign (%s): %v", c.Name, err)
-						continue
-					}
-					m.logger.Printf("start processing campaign (%s)", c.Name)
-
-					// If subscriber processing is busy, move on. Blocking and waiting
-					// can end up in a race condition where the waiting campaign's
-					// state in the data source has changed.
-					select {
-					case m.subFetchQueue <- c:
-					default:
-					}
-				}
+	go m.scanCampaigns(tick)
 
-				// Aggregate errors from sending messages to check against the error threshold
-				// after which a campaign is paused.
-			case e := <-m.campMsgErrorQueue:
-				if m.cfg.MaxSendErrors < 1 {
-					continue
-				}
-
-				// If the error threshold is met, pause the campaign.
-				m.campMsgErrorCounts[e.camp.ID]++
-				if m.campMsgErrorCounts[e.camp.ID] >= m.cfg.MaxSendErrors {
-					m.logger.Printf("error counted exceeded %d. pausing campaign %s",
-						m.cfg.MaxSendErrors, e.camp.Name)
-
-					if m.isCampaignProcessing(e.camp.ID) {
-						m.exhaustCampaign(e.camp, models.CampaignStatusPaused)
-					}
-					delete(m.campMsgErrorCounts, e.camp.ID)
-
-					// Notify admins.
-					m.sendNotif(e.camp, models.CampaignStatusPaused, "Too many errors")
-				}
-			}
-		}
-	}()
+	// Spawn N message workers.
+	for i := 0; i < m.cfg.Concurrency; i++ {
+		go m.messageWorker()
+	}
 
 	// Fetch the next set of subscribers for a campaign and process them.
 	for c := range m.subFetchQueue {
@@ -265,45 +219,41 @@ func (m *Manager) Run(tick time.Duration) {
 	}
 }
 
-// SpawnWorkers spawns workers goroutines that push out messages.
-func (m *Manager) SpawnWorkers() {
-	for i := 0; i < m.cfg.Concurrency; i++ {
-		go func() {
-			// Counter to keep track of the message / sec rate limit.
-			numMsg := 0
+// messageWorker is a blocking function that listens to the message queue
+// and pushes out incoming messages on it to the messenger.
+func (m *Manager) messageWorker() {
+	// Counter to keep track of the message / sec rate limit.
+	numMsg := 0
+	for {
+		select {
+		// Campaign message.
+		case msg := <-m.campMsgQueue:
+			// Pause on hitting the message rate.
+			if numMsg >= m.cfg.MessageRate {
+				time.Sleep(time.Second)
+				numMsg = 0
+			}
+			numMsg++
+
+			err := m.messengers[msg.Campaign.MessengerID].Push(
+				msg.from, []string{msg.to}, msg.subject, msg.body, nil)
+			if err != nil {
+				m.logger.Printf("error sending message in campaign %s: %v", msg.Campaign.Name, err)
 
-			for {
 				select {
-				// Campaign message.
-				case msg := <-m.campMsgQueue:
-					// Pause on hitting the message rate.
-					if numMsg >= m.cfg.MessageRate {
-						time.Sleep(time.Second)
-						numMsg = 0
-					}
-					numMsg++
-
-					err := m.messengers[msg.Campaign.MessengerID].Push(
-						msg.from, []string{msg.to}, msg.subject, msg.body, nil)
-					if err != nil {
-						m.logger.Printf("error sending message in campaign %s: %v", msg.Campaign.Name, err)
-
-						select {
-						case m.campMsgErrorQueue <- msgError{camp: msg.Campaign, err: err}:
-						default:
-						}
-					}
-
-				// Arbitrary message.
-				case msg := <-m.msgQueue:
-					err := m.messengers[msg.Messenger].Push(
-						msg.From, msg.To, msg.Subject, msg.Body, nil)
-					if err != nil {
-						m.logger.Printf("error sending message '%s': %v", msg.Subject, err)
-					}
+				case m.campMsgErrorQueue <- msgError{camp: msg.Campaign, err: err}:
+				default:
 				}
 			}
-		}()
+
+		// Arbitrary message.
+		case msg := <-m.msgQueue:
+			err := m.messengers[msg.Messenger].Push(
+				msg.From, msg.To, msg.Subject, msg.Body, nil)
+			if err != nil {
+				m.logger.Printf("error sending message '%s': %v", msg.Subject, err)
+			}
+		}
 	}
 }
 
@@ -338,6 +288,61 @@ func (m *Manager) TemplateFuncs(c *models.Campaign) template.FuncMap {
 	}
 }
 
+// scanCampaigns is a blocking function that periodically scans the data source
+// for campaigns to process and dispatches them to the manager.
+func (m *Manager) scanCampaigns(tick time.Duration) {
+	t := time.NewTicker(tick)
+	for {
+		select {
+		// Periodically scan the data source for campaigns to process.
+		case <-t.C:
+			campaigns, err := m.src.NextCampaigns(m.getPendingCampaignIDs())
+			if err != nil {
+				m.logger.Printf("error fetching campaigns: %v", err)
+				continue
+			}
+
+			for _, c := range campaigns {
+				if err := m.addCampaign(c); err != nil {
+					m.logger.Printf("error processing campaign (%s): %v", c.Name, err)
+					continue
+				}
+				m.logger.Printf("start processing campaign (%s)", c.Name)
+
+				// If subscriber processing is busy, move on. Blocking and waiting
+				// can end up in a race condition where the waiting campaign's
+				// state in the data source has changed.
+				select {
+				case m.subFetchQueue <- c:
+				default:
+				}
+			}
+
+			// Aggregate errors from sending messages to check against the error threshold
+			// after which a campaign is paused.
+		case e := <-m.campMsgErrorQueue:
+			if m.cfg.MaxSendErrors < 1 {
+				continue
+			}
+
+			// If the error threshold is met, pause the campaign.
+			m.campMsgErrorCounts[e.camp.ID]++
+			if m.campMsgErrorCounts[e.camp.ID] >= m.cfg.MaxSendErrors {
+				m.logger.Printf("error counted exceeded %d. pausing campaign %s",
+					m.cfg.MaxSendErrors, e.camp.Name)
+
+				if m.isCampaignProcessing(e.camp.ID) {
+					m.exhaustCampaign(e.camp, models.CampaignStatusPaused)
+				}
+				delete(m.campMsgErrorCounts, e.camp.ID)
+
+				// Notify admins.
+				m.sendNotif(e.camp, models.CampaignStatusPaused, "Too many errors")
+			}
+		}
+	}
+}
+
 // addCampaign adds a campaign to the process queue.
 func (m *Manager) addCampaign(c *models.Campaign) error {
 	// Validate messenger.

main.go

@@ -142,7 +142,6 @@ func main() {
 	// Start the campaign workers. The campaign batches (fetch from DB, push out
 	// messages) get processed at the specified interval.
 	go app.manager.Run(time.Second * 5)
-	app.manager.SpawnWorkers()
 
 	// Start and run the app server.
 	initHTTPServer(app)