add keep alive support

src/resource_pool.go

@@ -16,6 +16,7 @@ type ResourcePool struct {
 
 func (pool *ResourcePool) start() {
 	/* check dead nodes */
+	pool.heartBeat = map[string]time.Time{}
 	for k, v := range pool.heartBeat {
 		if v.Add(time.Second * 30).Before(time.Now()) {
 			delete(pool.nodes, k)