core, p2p/discv5: fix leaked goroutines

similar to ethereum#15696

Author: ferhatelmas

core/blockchain.go

@@ -1196,10 +1196,11 @@ func (bc *BlockChain) PostChainEvents(events []interface{}, logs []*types.Log) {
 }
 
 func (bc *BlockChain) update() {
-	futureTimer := time.Tick(5 * time.Second)
+	futureTimer := time.NewTicker(5 * time.Second)
+	defer futureTimer.Stop()
 	for {
 		select {
-		case <-futureTimer:
+		case <-futureTimer.C:
 			bc.procFutureBlocks()
 		case <-bc.quit:
 			return

p2p/discv5/database.go

@@ -239,14 +239,14 @@ func (db *nodeDB) ensureExpirer() {
 // expirer should be started in a go routine, and is responsible for looping ad
 // infinitum and dropping stale data from the database.
 func (db *nodeDB) expirer() {
-	tick := time.Tick(nodeDBCleanupCycle)
+	tick := time.NewTicker(nodeDBCleanupCycle)
+	defer tick.Stop()
 	for {
 		select {
-		case <-tick:
+		case <-tick.C:
 			if err := db.expireNodes(); err != nil {
 				log.Error(fmt.Sprintf("Failed to expire nodedb items: %v", err))
 			}
-
 		case <-db.quit:
 			return
 		}