Reduce allocs in AddPeer (#81)

* reduce allocs while adding peer

bucket.go

@@ -43,7 +43,7 @@ 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)
@@ -51,6 +51,28 @@ func (b *bucket) peers() []PeerInfo {
 	return ps
 }
 
+// returns the "minimum" peer in the bucket based on the `lessThan` comparator passed to it.
+// It is NOT safe for the comparator to mutate the given `PeerInfo`
+// as we pass in a pointer to it.
+// It is NOT safe to modify the returned value.
+func (b *bucket) min(lessThan func(p1 *PeerInfo, p2 *PeerInfo) bool) *PeerInfo {
+	if b.list.Len() == 0 {
+		return nil
+	}
+
+	minVal := b.list.Front().Value.(*PeerInfo)
+
+	for e := b.list.Front().Next(); e != nil; e = e.Next() {
+		val := e.Value.(*PeerInfo)
+
+		if lessThan(val, minVal) {
+			minVal = val
+		}
+	}
+
+	return minVal
+}
+
 // return the Ids of all the peers in the bucket.
 func (b *bucket) peerIds() []peer.ID {
 	ps := make([]peer.ID, 0, b.list.Len())

bucket_test.go

+package kbucket
+
+import (
+	"testing"
+	"time"
+
+	"github.com/libp2p/go-libp2p-core/test"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestBucketMinimum(t *testing.T) {
+	t.Parallel()
+
+	b := newBucket()
+	require.Nil(t, b.min(func(p1 *PeerInfo, p2 *PeerInfo) bool { return true }))
+
+	pid1 := test.RandPeerIDFatal(t)
+	pid2 := test.RandPeerIDFatal(t)
+	pid3 := test.RandPeerIDFatal(t)
+
+	// first is min
+	b.pushFront(&PeerInfo{Id: pid1, LastUsefulAt: time.Now()})
+	require.Equal(t, pid1, b.min(func(first *PeerInfo, second *PeerInfo) bool {
+		return first.LastUsefulAt.Before(second.LastUsefulAt)
+	}).Id)
+
+	// first is till min
+	b.pushFront(&PeerInfo{Id: pid2, LastUsefulAt: time.Now().AddDate(1, 0, 0)})
+	require.Equal(t, pid1, b.min(func(first *PeerInfo, second *PeerInfo) bool {
+		return first.LastUsefulAt.Before(second.LastUsefulAt)
+	}).Id)
+
+	// second is the min
+	b.pushFront(&PeerInfo{Id: pid3, LastUsefulAt: time.Now().AddDate(-1, 0, 0)})
+	require.Equal(t, pid3, b.min(func(first *PeerInfo, second *PeerInfo) bool {
+		return first.LastUsefulAt.Before(second.LastUsefulAt)
+	}).Id)
+}

table.go

@@ -183,18 +183,19 @@ 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 {
+	minLast := bucket.min(func(first *PeerInfo, second *PeerInfo) bool {
+		return first.LastUsefulAt.Before(second.LastUsefulAt)
+	})
+
+	if time.Since(minLast.LastUsefulAt) > rt.usefulnessGracePeriod {
 		// let's evict it and add the new peer
-			if bucket.remove(pc.Id) {
+		if bucket.remove(minLast.Id) {
 			bucket.pushFront(&PeerInfo{Id: p, LastUsefulAt: lastUsefulAt, LastSuccessfulOutboundQueryAt: time.Now(),
 				dhtId: ConvertPeerID(p)})
 			rt.PeerAdded(p)
 			return true, nil
 		}
 	}
-	}
 
 	return false, ErrPeerRejectedNoCapacity
 }

table_test.go

@@ -78,6 +78,7 @@ func TestBucket(t *testing.T) {
 			t.Fatalf("split failed. found id with cpl == 0 in non 0 bucket")
 		}
 	}
+
 }
 
 func TestNPeersForCpl(t *testing.T) {