- hide cdf and percentiles in LatencyRecorder::hide

- fix divide by zero error caused by output struct Stat while changing by sampling thread

src/bvar/latency_recorder.cpp

@@ -265,6 +265,8 @@ void LatencyRecorder::hide() {
     _latency_p3.hide();
     _latency_999.hide();
     _latency_9999.hide();
+    _latency_cdf.hide();
+    _latency_percentiles.hide();
 }
 
 LatencyRecorder& LatencyRecorder::operator<<(int64_t latency) {

src/bvar/recorder.h

@@ -35,16 +35,19 @@ struct Stat {
     int64_t num;
         
     int64_t get_average_int() const {
-        if (num == 0) {
+        //num can be changed by sampling thread, use tmp_num
+        int64_t tmp_num = num;
+        if (tmp_num == 0) {
             return 0;
         }
-        return sum / (int64_t)num;
+        return sum / (int64_t)tmp_num;
     }
     double get_average_double() const {
-        if (num == 0) {
+        int64_t tmp_num = num;
+        if (tmp_num == 0) {
             return 0.0;
         }
-        return (double)sum / (double)num;
+        return (double)sum / (double)tmp_num;
     }
     Stat operator-(const Stat& rhs) const {
         return Stat(sum - rhs.sum, num - rhs.num);