graph/db: let ChannelGraph init the graphCache

In this commit, we let the ChannelGraph be responsible for populating
the graphCache and then passing it to the KVStore. This is a first step
in moving the graphCache completely out of the KVStore layer.

graph/db/graph.go

@@ -1,6 +1,13 @@
 package graphdb
 
-import "github.com/lightningnetwork/lnd/kvdb"
+import (
+	"time"
+
+	"github.com/lightningnetwork/lnd/graph/db/models"
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/routing/route"
+)
 
 // Config is a struct that holds all the necessary dependencies for a
 // ChannelGraph.
@@ -20,17 +27,67 @@ type Config struct {
 // KVStore. Upcoming commits will move the graph cache out of the KVStore and
 // into this layer so that the KVStore is only responsible for CRUD operations.
 type ChannelGraph struct {
+	graphCache *GraphCache
+
 	*KVStore
 }
 
 // NewChannelGraph creates a new ChannelGraph instance with the given backend.
-func NewChannelGraph(cfg *Config) (*ChannelGraph, error) {
+func NewChannelGraph(cfg *Config, options ...ChanGraphOption) (*ChannelGraph,
+	error) {
+
+	opts := defaultChanGraphOptions()
+	for _, o := range options {
+		o(opts)
+	}
+
 	store, err := NewKVStore(cfg.KVDB, cfg.KVStoreOpts...)
 	if err != nil {
 		return nil, err
 	}
 
+	if !opts.useGraphCache {
+		return &ChannelGraph{
+			KVStore: store,
+		}, nil
+	}
+
+	// The graph cache can be turned off (e.g. for mobile users) for a
+	// speed/memory usage tradeoff.
+	graphCache := NewGraphCache(opts.preAllocCacheNumNodes)
+	startTime := time.Now()
+	log.Debugf("Populating in-memory channel graph, this might take a " +
+		"while...")
+
+	err = store.ForEachNodeCacheable(func(node route.Vertex,
+		features *lnwire.FeatureVector) error {
+
+		graphCache.AddNodeFeatures(node, features)
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	err = store.ForEachChannel(func(info *models.ChannelEdgeInfo,
+		policy1, policy2 *models.ChannelEdgePolicy) error {
+
+		graphCache.AddChannel(info, policy1, policy2)
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	log.Debugf("Finished populating in-memory channel graph (took %v, %s)",
+		time.Since(startTime), graphCache.Stats())
+
+	store.setGraphCache(graphCache)
+
 	return &ChannelGraph{
-		KVStore: store,
+		KVStore:    store,
+		graphCache: graphCache,
 	}, nil
 }