Merge pull request #1309 from fjl/p2p-fix-lookup-spin

p2p: throttle all discovery lookups

p2p/dial.go

@@ -17,10 +17,9 @@ const (
 	// redialing a certain node.
 	dialHistoryExpiration = 30 * time.Second
 
-	// Discovery lookup tasks will wait for this long when
+	// Discovery lookups are throttled and can only run
-	// no results are returned. This can happen if the table
+	// once every few seconds.
-	// becomes empty (i.e. not often).
+	lookupInterval = 4 * time.Second
-	emptyLookupDelay = 10 * time.Second
 )
 
 // dialstate schedules dials and discovery lookups.
@@ -206,18 +205,19 @@ func (t *dialTask) String() string {
 func (t *discoverTask) Do(srv *Server) {
 	if t.bootstrap {
 		srv.ntab.Bootstrap(srv.BootstrapNodes)
-	} else {
+		return
+	}
+	// newTasks generates a lookup task whenever dynamic dials are
+	// necessary. Lookups need to take some time, otherwise the
+	// event loop spins too fast.
+	next := srv.lastLookup.Add(lookupInterval)
+	if now := time.Now(); now.Before(next) {
+		time.Sleep(next.Sub(now))
+	}
+	srv.lastLookup = time.Now()
 	var target discover.NodeID
 	rand.Read(target[:])
 	t.results = srv.ntab.Lookup(target)
-		// newTasks generates a lookup task whenever dynamic dials are
-		// necessary. Lookups need to take some time, otherwise the
-		// event loop spins too fast. An empty result can only be
-		// returned if the table is empty.
-		if len(t.results) == 0 {
-			time.Sleep(emptyLookupDelay)
-		}
-	}
 }
 
 func (t *discoverTask) String() (s string) {

p2p/server.go

@@ -115,6 +115,7 @@ type Server struct {
 	ntab         discoverTable
 	listener     net.Listener
 	ourHandshake *protoHandshake
+	lastLookup   time.Time
 
 	// These are for Peers, PeerCount (and nothing else).
 	peerOp     chan peerOpFunc