discovery: allow the SyncManager to report whether the graph is synced

discovery/sync_manager.go

@@ -3,6 +3,7 @@ package discovery
 import (
 	"errors"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -100,6 +101,16 @@ type SyncManagerCfg struct {
 // attempt a historical sync to ensure we have as much of the public channel
 // graph as possible.
 type SyncManager struct {
+	// initialHistoricalSyncCompleted serves as a barrier when initializing
+	// new active GossipSyncers. If 0, the initial historical sync has not
+	// completed, so we'll defer initializing any active GossipSyncers. If
+	// 1, then we can transition the GossipSyncer immediately. We set up
+	// this barrier to ensure we have most of the graph before attempting to
+	// accept new updates at tip.
+	//
+	// NOTE: This must be used atomically.
+	initialHistoricalSyncCompleted int32
+
 	start sync.Once
 	stop  sync.Once
 
@@ -192,15 +203,6 @@ func (m *SyncManager) syncerHandler() {
 	defer m.cfg.HistoricalSyncTicker.Stop()
 
 	var (
-		// initialHistoricalSyncCompleted serves as a barrier when
-		// initializing new active GossipSyncers. If false, the initial
-		// historical sync has not completed, so we'll defer
-		// initializing any active GossipSyncers. If true, then we can
-		// transition the GossipSyncer immediately. We set up this
-		// barrier to ensure we have most of the graph before attempting
-		// to accept new updates at tip.
-		initialHistoricalSyncCompleted = false
-
 		// initialHistoricalSyncer is the syncer we are currently
 		// performing an initial historical sync with.
 		initialHistoricalSyncer *GossipSyncer
@@ -251,10 +253,10 @@ func (m *SyncManager) syncerHandler() {
 				fallthrough
 
 			// If the initial historical sync has yet to complete,
-			// then we'll declare is as passive and attempt to
+			// then we'll declare it as passive and attempt to
 			// transition it when the initial historical sync
 			// completes.
-			case !initialHistoricalSyncCompleted:
+			case !m.IsGraphSynced():
 				s.setSyncType(PassiveSync)
 				m.inactiveSyncers[s.cfg.peerPub] = s
 
@@ -279,7 +281,7 @@ func (m *SyncManager) syncerHandler() {
 			if !attemptHistoricalSync {
 				continue
 			}
-			initialHistoricalSyncCompleted = false
+			m.markGraphSyncing()
 
 			log.Debugf("Attempting initial historical sync with "+
 				"GossipSyncer(%x)", s.cfg.peerPub)
@@ -344,7 +346,7 @@ func (m *SyncManager) syncerHandler() {
 		case <-initialHistoricalSyncSignal:
 			initialHistoricalSyncer = nil
 			initialHistoricalSyncSignal = nil
-			initialHistoricalSyncCompleted = true
+			m.markGraphSynced()
 
 			log.Debug("Initial historical sync completed")
 
@@ -667,3 +669,22 @@ func (m *SyncManager) gossipSyncers() map[route.Vertex]*GossipSyncer {
 
 	return syncers
 }
+
+// markGraphSynced allows us to report that the initial historical sync has
+// completed.
+func (m *SyncManager) markGraphSynced() {
+	atomic.StoreInt32(&m.initialHistoricalSyncCompleted, 1)
+}
+
+// markGraphSyncing allows us to report that the initial historical sync is
+// still undergoing.
+func (m *SyncManager) markGraphSyncing() {
+	atomic.StoreInt32(&m.initialHistoricalSyncCompleted, 0)
+}
+
+// IsGraphSynced determines whether we've completed our initial historical sync.
+// The initial historical sync is done to ensure we've ingested as much of the
+// public graph as possible.
+func (m *SyncManager) IsGraphSynced() bool {
+	return atomic.LoadInt32(&m.initialHistoricalSyncCompleted) == 1
+}