discovery: simplify chooseRandomSyncer helper

discovery/sync_manager.go

@@ -318,17 +318,13 @@ func (m *SyncManager) removeGossipSyncer(peer routing.Vertex) {
 
 	// Otherwise, we'll need find a new one to replace it, if any.
 	delete(m.activeSyncers, peer)
-	newActiveSyncer := m.chooseRandomSyncer(nil, false)
+	newActiveSyncer := chooseRandomSyncer(
+		m.inactiveSyncers, m.transitionPassiveSyncer,
+	)
 	if newActiveSyncer == nil {
 		return
 	}
 
-	if err := m.transitionPassiveSyncer(newActiveSyncer); err != nil {
-		log.Errorf("Unable to transition passive GossipSyncer(%x): %v",
-			newActiveSyncer.cfg.peerPub, err)
-		return
-	}
-
 	log.Debugf("Replaced active GossipSyncer(%x) with GossipSyncer(%x)",
 		peer, newActiveSyncer.cfg.peerPub)
 }
@@ -340,30 +336,19 @@ func (m *SyncManager) rotateActiveSyncerCandidate() {
 	m.syncersMu.Lock()
 	defer m.syncersMu.Unlock()
 
-	// If we don't have a candidate to rotate with, we can return early.
-	candidate := m.chooseRandomSyncer(nil, false)
-	if candidate == nil {
-		log.Debug("No eligible candidate to rotate active syncer")
+	// If we couldn't find an eligible active syncer to rotate, we can
+	// return early.
+	activeSyncer := chooseRandomSyncer(m.activeSyncers, nil)
+	if activeSyncer == nil {
+		log.Debug("No eligible active syncer to rotate")
 		return
 	}
 
-	// We'll choose an active syncer at random that's within a chansSynced
-	// state to rotate.
-	var activeSyncer *GossipSyncer
-	for _, s := range m.activeSyncers {
-		// The active syncer must be in a chansSynced state in order to
-		// process sync transitions.
-		if s.syncState() != chansSynced {
-			continue
-		}
-
-		activeSyncer = s
-		break
-	}
-
-	// If we couldn't find an eligible one, we can return early.
-	if activeSyncer == nil {
-		log.Debug("No eligible active syncer to rotate")
+	// Similarly, if we don't have a candidate to rotate with, we can return
+	// early as well.
+	candidate := chooseRandomSyncer(m.inactiveSyncers, nil)
+	if candidate == nil {
+		log.Debug("No eligible candidate to rotate active syncer")
 		return
 	}
 
@@ -425,72 +410,39 @@ func (m *SyncManager) forceHistoricalSync() {
 	m.syncersMu.Lock()
 	defer m.syncersMu.Unlock()
 
-	// We'll choose a random peer with whom we can perform a historical sync
-	// with. We'll set useActive to true to make sure we can still do one if
-	// we don't happen to have any non-active syncers.
-	candidatesChosen := make(map[routing.Vertex]struct{})
-	s := m.chooseRandomSyncer(candidatesChosen, true)
-	for s != nil {
-		// Ensure we properly handle a shutdown signal.
-		select {
-		case <-m.quit:
-			return
-		default:
-		}
-
-		// Blacklist the candidate to ensure it's not chosen again.
-		candidatesChosen[s.cfg.peerPub] = struct{}{}
-
-		err := s.historicalSync()
-		if err == nil {
-			return
-		}
-
-		log.Errorf("Unable to perform historical sync with "+
-			"GossipSyncer(%x): %v", s.cfg.peerPub, err)
-
-		s = m.chooseRandomSyncer(candidatesChosen, true)
-	}
+	// We'll sample from both sets of active and inactive syncers in the
+	// event that we don't have any inactive syncers.
+	_ = chooseRandomSyncer(m.gossipSyncers(), func(s *GossipSyncer) error {
+		return s.historicalSync()
+	})
 }
 
-// chooseRandomSyncer returns a random non-active syncer that's eligible for a
-// sync transition. A blacklist can be used to skip any previously chosen
-// candidates. The useActive boolean can be used to also filter active syncers.
+// chooseRandomSyncer iterates through the set of syncers given and returns the
+// first one which was able to successfully perform the action enclosed in the
+// function closure.
 //
 // NOTE: It's possible for a nil value to be returned if there are no eligible
 // candidate syncers.
-//
-// NOTE: This method must be called with the syncersMtx lock held.
-func (m *SyncManager) chooseRandomSyncer(blacklist map[routing.Vertex]struct{},
-	useActive bool) *GossipSyncer {
-
-	eligible := func(s *GossipSyncer) bool {
-		// Skip any syncers that exist within the blacklist.
-		if blacklist != nil {
-			if _, ok := blacklist[s.cfg.peerPub]; ok {
-				return false
-			}
-		}
+func chooseRandomSyncer(syncers map[routing.Vertex]*GossipSyncer,
+	action func(*GossipSyncer) error) *GossipSyncer {
 
+	for _, s := range syncers {
 		// Only syncers in a chansSynced state are viable for sync
 		// transitions, so skip any that aren't.
-		return s.syncState() == chansSynced
-	}
-
-	for _, s := range m.inactiveSyncers {
-		if !eligible(s) {
+		if s.syncState() != chansSynced {
 			continue
 		}
-		return s
-	}
 
-	if useActive {
-		for _, s := range m.activeSyncers {
-			if !eligible(s) {
+		if action != nil {
+			if err := action(s); err != nil {
+				log.Debugf("Skipping eligible candidate "+
+					"GossipSyncer(%x): %v", s.cfg.peerPub,
+					err)
 				continue
 			}
-			return s
 		}
+
+		return s
 	}
 
 	return nil
@@ -573,7 +525,11 @@ func (m *SyncManager) gossipSyncer(peer routing.Vertex) (*GossipSyncer, bool) {
 func (m *SyncManager) GossipSyncers() map[routing.Vertex]*GossipSyncer {
 	m.syncersMu.Lock()
 	defer m.syncersMu.Unlock()
+	return m.gossipSyncers()
+}
 
+// gossipSyncers returns all of the currently initialized gossip syncers.
+func (m *SyncManager) gossipSyncers() map[routing.Vertex]*GossipSyncer {
 	numSyncers := len(m.inactiveSyncers) + len(m.activeSyncers)
 	syncers := make(map[routing.Vertex]*GossipSyncer, numSyncers)