Speed up latest entry lookup by using the cache if it's not empty

shroom_internals/cache.go

@@ -12,6 +12,20 @@ type DataCache struct {
 	start int
 }
 
+func (dc *DataCache) LatestTime() int64 {
+	dc.Lock()
+	defer dc.Unlock()
+
+	if len(dc.data) == 0 {
+		return -1
+	}
+	if dc.start == 0 {
+		return int64(dc.data[len(dc.data)-1].Time)
+	} else {
+		return int64(dc.data[dc.start-1].Time)
+	}
+}
+
 func (dc *DataCache) Add(data *Datapoint) {
 	dc.Lock()
 	defer dc.Unlock()

shroom_server.go

@@ -106,6 +106,19 @@ func main() {
 	dumpSecond := dumpData(db, &state.Cache, 1000)
 
 	lastPoint := func(w http.ResponseWriter, _req *http.Request) {
+		var err error
+		time := state.Cache.LatestTime()
+		if time > 0 {
+			msg, err := json.Marshal(time)
+			if err != nil {
+				w.WriteHeader(500)
+				w.Write([]byte(err.Error()))
+			} else {
+				w.Write(msg)
+			}
+			return
+		}
+
 		msg, err := s.LastTime(db)
 		if err != nil {
 			w.WriteHeader(500)