[metric] static summary serialize won't empty when it has observerd a… (

#898)

[metric] static summary serialize won't empty when it has observerd and refreshed

include/ylt/metric/summary.hpp

@@ -58,7 +58,10 @@ class summary_t : public static_metric {
       std::sort(quantiles_.begin(), quantiles_.end());
   }
 
-  void observe(float value) { impl_.insert(value); }
+  void observe(float value) {
+    has_refreshed_.store(true, std::memory_order_relaxed);
+    impl_.insert(value);
+  }
 
   std::vector<float> get_rates() {
     uint64_t count;
@@ -85,7 +88,7 @@ class summary_t : public static_metric {
     double sum = 0;
     uint64_t count = 0;
     auto rates = get_rates(sum, count);
-    if (count == 0) {
+    if (count == 0 && !has_refreshed_.load(std::memory_order_relaxed)) {
       return;
     }
     serialize_head(str);
@@ -121,7 +124,7 @@ class summary_t : public static_metric {
     json_summary_metric_t metric;
 
     metric.quantiles_value = get_rates(metric.sum, metric.count);
-    if (metric.count == 0) {
+    if (metric.count == 0 && !has_refreshed_.load(std::memory_order_relaxed)) {
       return;
     }
     metric.labels.reserve(labels_value_.size());
@@ -132,6 +135,7 @@ class summary_t : public static_metric {
 #endif
 
  private:
+  std::atomic<bool> has_refreshed_;
   std::vector<double> quantiles_;
   ylt::metric::detail::summary_impl<uint64_t> impl_;
 };

src/metric/tests/test_metric.cpp

@@ -978,9 +978,24 @@ TEST_CASE("test summary refresh") {
   std::random_device rd;
   std::mt19937 gen(rd());
   std::uniform_int_distribution<> distr(1, 100);
+  std::string str;
+  summary.serialize_to_json(str);
+  CHECK(str.size() == 0);
+  str = "";
+  summary.serialize(str);
+  CHECK(str.size() == 0);
+
+  std::this_thread::sleep_for(1001ms);
+  summary.serialize_to_json(str);
+  CHECK(str.size() == 0);
+  str = "";
+  summary.serialize(str);
+  CHECK(str.size() == 0);
+
   for (int i = 0; i < 50; i++) {
     summary.observe(i);
   }
+
   double sum;
   uint64_t cnt;
   summary.get_rates(sum, cnt);
@@ -1002,7 +1017,11 @@ TEST_CASE("test summary refresh") {
   CHECK(cnt == 10);
   std::this_thread::sleep_for(500ms);
   summary.get_rates(sum, cnt);
-  CHECK(cnt == 0);
+  summary.serialize_to_json(str);
+  CHECK(str.size() > 0);
+  str = "";
+  summary.serialize(str);
+  CHECK(str.size() > 0);
 }
 
 TEST_CASE("test register metric") {