Revert "agent: refactor sync loop to linear flow of control"

This reverts commit 7a2af206ea.

agent/ae/ae.go

@@ -93,67 +93,66 @@ func (s *StateSyncer) Run() {
 
 Sync:
 	for {
-		switch err := s.State.UpdateSyncState(); {
-
-		// update sync status failed
-		case err != nil:
-			s.Logger.Printf("[ERR] agent: failed to sync remote state: %v", err)
-
-			// retry updating sync status after some time or when a consul
-			// server was added.
-			select {
+		// update the sync status
+		err := s.State.UpdateSyncState()
+		if err == nil {
+			break
+		}
 
-			// consul server added to cluster.
-			// retry sooner than retryFailIntv to converge cluster sooner
-			// but stagger delay to avoid thundering herd
-			case <-s.ServerUpCh:
-				select {
-				case <-time.After(stagger(serverUpIntv)):
-				case <-s.ShutdownCh:
-					return
-				}
+		s.Logger.Printf("[ERR] agent: failed to sync remote state: %v", err)
 
-			// retry full sync after some time
-			// todo(fs): why don't we use s.Interval here?
-			case <-time.After(retryFailIntv + stagger(retryFailIntv)):
+		// retry updating sync status after some time or when a consul
+		// server was added.
+		select {
 
+		// consul server added to cluster.
+		// retry sooner than retryFailIntv to converge cluster quicker
+		// but stagger delay to avoid thundering herd
+		case <-s.ServerUpCh:
+			select {
+			case <-time.After(stagger(serverUpIntv)):
 			case <-s.ShutdownCh:
 				return
 			}
 
-		// update sync status OK
-		default:
-			// force-trigger sync to pickup any changes
-			s.triggerSync()
-
-			// do partial syncs until it is time for a full sync again
-			for {
-				select {
-				// todo(fs): why don't we honor the ServerUpCh here as well?
-				// todo(fs): by default, s.Interval is 60s which is >> 3s (serverUpIntv)
-				// case <-s.ServerUpCh:
-				// 	select {
-				// 	case <-time.After(stagger(serverUpIntv)):
-				// 		continue Sync
-				// 	case <-s.ShutdownCh:
-				// 		return
-				// 	}
-
-				case <-time.After(s.Interval + stagger(s.Interval)):
-					continue Sync
-
-				case <-s.TriggerCh:
-					if s.Paused() {
-						continue
-					}
-					if err := s.State.SyncChanges(); err != nil {
-						s.Logger.Printf("[ERR] agent: failed to sync changes: %v", err)
-					}
-
-				case <-s.ShutdownCh:
-					return
-				}
+		// retry full sync after some time
+		// todo(fs): why don't we use s.Interval here?
+		case <-time.After(retryFailIntv + stagger(retryFailIntv)):
+
+		case <-s.ShutdownCh:
+			return
+		}
+	}
+
+	// Force-trigger sync to pickup any changes
+	s.triggerSync()
+
+	// Wait for sync events
+	for {
+		select {
+		// todo(fs): why don't we honor the ServerUpCh here as well?
+		// todo(fs): by default, s.Interval is 60s which is >> 3s (serverUpIntv)
+		// case <-s.ServerUpCh:
+		// 	select {
+		// 	case <-time.After(stagger(serverUpIntv)):
+		// 		continue Sync
+		// 	case <-s.ShutdownCh:
+		// 		return
+		// 	}
+
+		case <-time.After(s.Interval + stagger(s.Interval)):
+			goto Sync
+
+		case <-s.TriggerCh:
+			if s.Paused() {
+				continue
+			}
+			if err := s.State.SyncChanges(); err != nil {
+				s.Logger.Printf("[ERR] agent: failed to sync changes: %v", err)
 			}
+
+		case <-s.ShutdownCh:
+			return
 		}
 	}
 }