Reduce allocs in AddPeer

bucket.go

@@ -43,14 +43,27 @@ func newBucket() *bucket {
 // returns all peers in the bucket
 // it is safe for the caller to modify the returned objects as it is a defensive copy
 func (b *bucket) peers() []PeerInfo {
-	var ps []PeerInfo
+	ps := make([]PeerInfo, 0, b.len())
 	for e := b.list.Front(); e != nil; e = e.Next() {
 		p := e.Value.(*PeerInfo)
 		ps = append(ps, *p)
 	}
 	return ps
 }
 
+// returns the first peer in the bucket that satisfies the given predicate.
+// It is NOT safe for the predicate to mutate the given `PeerInfo`
+// as we pass in a pointer to it.
+func (b *bucket) selectFirst(predicate func(p *PeerInfo) bool) peer.ID {
+	for e := b.list.Front(); e != nil; e = e.Next() {
+		p := e.Value.(*PeerInfo)
+		if predicate(p) {
+			return p.Id
+		}
+	}
+	return ""
+}
+
 // return the Ids of all the peers in the bucket.
 func (b *bucket) peerIds() []peer.ID {
 	ps := make([]peer.ID, 0, b.list.Len())

table.go

@@ -152,16 +152,16 @@ func (rt *RoutingTable) addPeer(p peer.ID, queryPeer bool) (bool, error) {
 
 	// the bucket to which the peer belongs is full. Let's try to find a peer
 	// in that bucket with a LastSuccessfulOutboundQuery value above the maximum threshold and replace it.
-	allPeers := bucket.peers()
-	for _, pc := range allPeers {
-		if time.Since(pc.LastUsefulAt) > rt.usefulnessGracePeriod {
-			// let's evict it and add the new peer
-			if bucket.remove(pc.Id) {
-				bucket.pushFront(&PeerInfo{Id: p, LastUsefulAt: lastUsefulAt, LastSuccessfulOutboundQueryAt: time.Now(),
-					dhtId: ConvertPeerID(p)})
-				rt.PeerAdded(p)
-				return true, nil
-			}
+	pid := bucket.selectFirst(func(pi *PeerInfo) bool {
+		return time.Since(pi.LastUsefulAt) > rt.usefulnessGracePeriod
+	})
+	if pid != "" {
+		// let's evict it and add the new peer
+		if bucket.remove(pid) {
+			bucket.pushFront(&PeerInfo{Id: p, LastUsefulAt: lastUsefulAt, LastSuccessfulOutboundQueryAt: time.Now(),
+				dhtId: ConvertPeerID(p)})
+			rt.PeerAdded(p)
+			return true, nil
 		}
 	}
 

table_test.go

@@ -60,6 +60,11 @@ func TestBucket(t *testing.T) {
 	require.EqualValues(t, t2, p.LastSuccessfulOutboundQueryAt)
 	require.EqualValues(t, t3, p.LastUsefulAt)
 
+	p.Id = peer.ID("randid")
+	require.EqualValues(t, "randid", b.selectFirst(func(pi *PeerInfo) bool {
+		return pi.Id == "randid"
+	}))
+
 	spl := b.split(0, ConvertPeerID(local))
 	llist := b.list
 	for e := llist.Front(); e != nil; e = e.Next() {
@@ -78,6 +83,7 @@ func TestBucket(t *testing.T) {
 			t.Fatalf("split failed. found id with cpl == 0 in non 0 bucket")
 		}
 	}
+
 }
 
 func TestRemovePeer(t *testing.T) {