Support to hide metrics which hasn't update for a long time

core/CMakeLists.txt

@@ -7,6 +7,7 @@ add_library(core
   src/detail/time_window_quantiles.cc
   src/detail/utils.cc
   src/family.cc
+  src/metric.cc
   src/gauge.cc
   src/histogram.cc
   src/registry.cc

core/include/prometheus/counter.h

@@ -4,6 +4,7 @@
 #include "prometheus/detail/builder.h"  // IWYU pragma: export
 #include "prometheus/detail/core_export.h"
 #include "prometheus/gauge.h"
+#include "prometheus/metric.h"
 #include "prometheus/metric_type.h"
 
 namespace prometheus {
@@ -23,7 +24,7 @@ namespace prometheus {
 ///
 /// The class is thread-safe. No concurrent call to any API of this type causes
 /// a data race.
-class PROMETHEUS_CPP_CORE_EXPORT Counter {
+class PROMETHEUS_CPP_CORE_EXPORT Counter : public Metric {
  public:
   static const MetricType metric_type{MetricType::Counter};
 

core/include/prometheus/gauge.h

@@ -5,6 +5,7 @@
 #include "prometheus/client_metric.h"
 #include "prometheus/detail/builder.h"  // IWYU pragma: export
 #include "prometheus/detail/core_export.h"
+#include "prometheus/metric.h"
 #include "prometheus/metric_type.h"
 
 namespace prometheus {
@@ -21,7 +22,7 @@ namespace prometheus {
 ///
 /// The class is thread-safe. No concurrent call to any API of this type causes
 /// a data race.
-class PROMETHEUS_CPP_CORE_EXPORT Gauge {
+class PROMETHEUS_CPP_CORE_EXPORT Gauge : public Metric {
  public:
   static const MetricType metric_type{MetricType::Gauge};
 

core/include/prometheus/histogram.h

@@ -7,6 +7,7 @@
 #include "prometheus/detail/builder.h"  // IWYU pragma: export
 #include "prometheus/detail/core_export.h"
 #include "prometheus/gauge.h"
+#include "prometheus/metric.h"
 #include "prometheus/metric_type.h"
 
 namespace prometheus {
@@ -27,7 +28,7 @@ namespace prometheus {
 ///
 /// The class is thread-safe. No concurrent call to any API of this type causes
 /// a data race.
-class PROMETHEUS_CPP_CORE_EXPORT Histogram {
+class PROMETHEUS_CPP_CORE_EXPORT Histogram : public Metric {
  public:
   using BucketBoundaries = std::vector<double>;
 

core/include/prometheus/metric.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <ctime>
+
+#include "prometheus/detail/core_export.h"
+#include "prometheus/metric_type.h"
+
+namespace prometheus {
+
+/// \brief The base metric.
+///
+class PROMETHEUS_CPP_CORE_EXPORT Metric {
+ public:
+  static const MetricType metric_type{MetricType::Untyped};
+
+  Metric();
+  virtual ~Metric() = default;
+
+  bool Expired(time_t current_ts) const;
+
+ protected:
+  void UpdateTS();
+
+ private:
+  time_t last_update_ts_;
+};
+
+}  // namespace prometheus

core/include/prometheus/summary.h

@@ -10,6 +10,7 @@
 #include "prometheus/detail/ckms_quantiles.h"
 #include "prometheus/detail/core_export.h"
 #include "prometheus/detail/time_window_quantiles.h"
+#include "prometheus/metric.h"
 #include "prometheus/metric_type.h"
 
 namespace prometheus {
@@ -38,7 +39,7 @@ namespace prometheus {
 ///
 /// The class is thread-safe. No concurrent call to any API of this type causes
 /// a data race.
-class PROMETHEUS_CPP_CORE_EXPORT Summary {
+class PROMETHEUS_CPP_CORE_EXPORT Summary : public Metric {
  public:
   using Quantiles = std::vector<detail::CKMSQuantiles::Quantile>;
 

core/src/counter.cc

@@ -2,13 +2,17 @@
 
 namespace prometheus {
 
-void Counter::Increment() { gauge_.Increment(); }
+void Counter::Increment() {
+  gauge_.Increment();
+  UpdateTS();
+}
 
 void Counter::Increment(const double val) {
   if (val < 0.0) {
     return;
   }
   gauge_.Increment(val);
+  UpdateTS();
 }
 
 double Counter::Value() const { return gauge_.Value(); }

core/src/family.cc

@@ -96,6 +96,7 @@ const std::map<std::string, std::string> Family<T>::GetConstantLabels() const {
 
 template <typename T>
 std::vector<MetricFamily> Family<T>::Collect() const {
+  auto current_ts = std::time(nullptr);
   std::lock_guard<std::mutex> lock{mutex_};
 
   if (metrics_.empty()) {
@@ -108,7 +109,10 @@ std::vector<MetricFamily> Family<T>::Collect() const {
   family.type = T::metric_type;
   family.metric.reserve(metrics_.size());
   for (const auto& m : metrics_) {
-    family.metric.push_back(std::move(CollectMetric(m.first, m.second.get())));
+    if (!m.second->Expired(current_ts)) {
+      family.metric.push_back(
+          std::move(CollectMetric(m.first, m.second.get())));
+    }
   }
   return {family};
 }

core/src/gauge.cc

@@ -14,12 +14,16 @@ void Gauge::Decrement() { Decrement(1.0); }
 
 void Gauge::Decrement(const double value) { Change(-1.0 * value); }
 
-void Gauge::Set(const double value) { value_.store(value); }
+void Gauge::Set(const double value) {
+  value_.store(value);
+  UpdateTS();
+}
 
 void Gauge::Change(const double value) {
   auto current = value_.load();
   while (!value_.compare_exchange_weak(current, current + value))
     ;
+  UpdateTS();
 }
 
 void Gauge::SetToCurrentTime() {

core/src/histogram.cc

@@ -26,6 +26,7 @@ void Histogram::Observe(const double value) {
           [value](const double boundary) { return boundary >= value; })));
   sum_.Increment(value);
   bucket_counts_[bucket_index].Increment();
+  UpdateTS();
 }
 
 void Histogram::ObserveMultiple(const std::vector<double>& bucket_increments,
@@ -41,6 +42,7 @@ void Histogram::ObserveMultiple(const std::vector<double>& bucket_increments,
   for (std::size_t i{0}; i < bucket_counts_.size(); ++i) {
     bucket_counts_[i].Increment(bucket_increments[i]);
   }
+  UpdateTS();
 }
 
 ClientMetric Histogram::Collect() const {

core/src/metric.cc

@@ -0,0 +1,19 @@
+#include "prometheus/metric.h"
+
+#include <ctime>
+
+namespace prometheus {
+
+Metric::Metric() : last_update_ts_(std::time(nullptr)) {
+}
+
+bool Metric::Expired(time_t current_ts) const {
+  static const double retire_time = 600;
+  return difftime(current_ts, last_update_ts_) > retire_time;
+}
+
+void Metric::UpdateTS() {
+  last_update_ts_ = std::time(nullptr);
+}
+
+}  // namespace prometheus

core/src/summary.cc

@@ -17,6 +17,7 @@ void Summary::Observe(const double value) {
   count_ += 1;
   sum_ += value;
   quantile_values_.insert(value);
+  UpdateTS();
 }
 
 ClientMetric Summary::Collect() const {