Add logic to refrain from exporting un-updated metric instruments

sdk/include/opentelemetry/sdk/metrics/aggregator/aggregator.h

@@ -97,6 +97,14 @@ class Aggregator
    */
   virtual AggregatorKind get_aggregator_kind() final { return agg_kind_; }
 
+  /**
+   * Getter function for updated_ protected var
+   *
+   * @return A bool indicating wether or not this aggregator has been updated
+   * in the most recent collection interval.
+   */
+  virtual bool is_updated() final { return updated_; }
+
   // virtual function to be overriden for the Histogram Aggregator
   virtual std::vector<double> get_boundaries() { return std::vector<double>(); }
 
@@ -134,6 +142,7 @@ class Aggregator
   opentelemetry::metrics::InstrumentKind kind_;
   std::mutex mu_;
   AggregatorKind agg_kind_;
+  bool updated_;
 };
 
 }  // namespace metrics

sdk/include/opentelemetry/sdk/metrics/aggregator/counter_aggregator.h

@@ -36,6 +36,7 @@ class CounterAggregator final : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
+    this->updated_ = true;
     this->values_[0] += val;  // atomic operation
     this->mu_.unlock();
   }
@@ -50,6 +51,7 @@ class CounterAggregator final : public Aggregator<T>
   void checkpoint() override
   {
     this->mu_.lock();
+    this->updated_    = false;
     this->checkpoint_ = this->values_;
     this->values_[0]  = 0;
     this->mu_.unlock();

sdk/include/opentelemetry/sdk/metrics/aggregator/exact_aggregator.h

@@ -62,6 +62,7 @@ class ExactAggregator : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
+    this->updated_ = true;
     this->values_.push_back(val);
     this->mu_.unlock();
   }
@@ -74,6 +75,7 @@ class ExactAggregator : public Aggregator<T>
   void checkpoint() override
   {
     this->mu_.lock();
+    this->updated_ = false;
     if (quant_estimation_)
     {
       std::sort(this->values_.begin(), this->values_.end());

sdk/include/opentelemetry/sdk/metrics/aggregator/gauge_aggregator.h

@@ -59,6 +59,7 @@ class GaugeAggregator : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
+    this->updated_     = true;
     this->values_[0]   = val;
     current_timestamp_ = core::SystemTimestamp(std::chrono::system_clock::now());
     this->mu_.unlock();
@@ -75,6 +76,7 @@ class GaugeAggregator : public Aggregator<T>
   {
     this->mu_.lock();
 
+    this->updated_    = false;
     this->checkpoint_ = this->values_;
 
     // Reset the values to default

sdk/include/opentelemetry/sdk/metrics/aggregator/histogram_aggregator.h

@@ -63,7 +63,8 @@ class HistogramAggregator final : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
-    int bucketID = boundaries_.size();
+    this->updated_ = true;
+    int bucketID   = boundaries_.size();
     for (size_t i = 0; i < boundaries_.size(); i++)
     {
       if (val < boundaries_[i])  // concurrent read is thread-safe
@@ -93,6 +94,7 @@ class HistogramAggregator final : public Aggregator<T>
   void checkpoint() override
   {
     this->mu_.lock();
+    this->updated_     = false;
     this->checkpoint_  = this->values_;
     this->values_[0]   = 0;
     this->values_[1]   = 0;

sdk/include/opentelemetry/sdk/metrics/aggregator/min_max_sum_count_aggregator.h

@@ -60,6 +60,7 @@ class MinMaxSumCountAggregator : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
+    this->updated_ = true;
 
     if (this->values_[CountValueIndex] == 0 || val < this->values_[MinValueIndex])  // set min
       this->values_[MinValueIndex] = val;
@@ -80,6 +81,7 @@ class MinMaxSumCountAggregator : public Aggregator<T>
   void checkpoint() override
   {
     this->mu_.lock();
+    this->updated_    = false;
     this->checkpoint_ = this->values_;
     // Reset the values
     this->values_[MinValueIndex]   = 0;

sdk/include/opentelemetry/sdk/metrics/aggregator/sketch_aggregator.h

@@ -64,6 +64,7 @@ class SketchAggregator final : public Aggregator<T>
   void update(T val) override
   {
     this->mu_.lock();
+    this->updated_ = true;
     int idx;
     if (val == 0)
     {
@@ -130,6 +131,7 @@ class SketchAggregator final : public Aggregator<T>
   void checkpoint() override
   {
     this->mu_.lock();
+    this->updated_    = false;
     this->checkpoint_ = this->values_;
     checkpoint_raw_   = raw_;
     this->values_[0]  = 0;

sdk/include/opentelemetry/sdk/metrics/sync_instruments.h

@@ -149,8 +149,11 @@ class Counter final : public SynchronousInstrument<T>, public metrics_api::Count
         toDelete.push_back(x.first);
       }
       auto agg_ptr = dynamic_cast<BoundCounter<T> *>(x.second.get())->GetAggregator();
-      agg_ptr->checkpoint();
-      ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      if (agg_ptr->is_updated())
+      {
+        agg_ptr->checkpoint();
+        ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      }
     }
     for (const auto &x : toDelete)
     {
@@ -273,8 +276,11 @@ class UpDownCounter final : public SynchronousInstrument<T>, public metrics_api:
         toDelete.push_back(x.first);
       }
       auto agg_ptr = dynamic_cast<BoundUpDownCounter<T> *>(x.second.get())->GetAggregator();
-      agg_ptr->checkpoint();
-      ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      if (agg_ptr->is_updated())
+      {
+        agg_ptr->checkpoint();
+        ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      }
     }
     for (const auto &x : toDelete)
     {
@@ -396,8 +402,11 @@ class ValueRecorder final : public SynchronousInstrument<T>, public metrics_api:
         toDelete.push_back(x.first);
       }
       auto agg_ptr = dynamic_cast<BoundValueRecorder<T> *>(x.second.get())->GetAggregator();
-      agg_ptr->checkpoint();
-      ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      if (agg_ptr->is_updated())
+      {
+        agg_ptr->checkpoint();
+        ret.push_back(Record(x.second->GetName(), x.second->GetDescription(), x.first, agg_ptr));
+      }
     }
     for (const auto &x : toDelete)
     {

sdk/test/metrics/metric_instrument_test.cc

@@ -248,6 +248,7 @@ TEST(Counter, getAggsandnewupdate)
 
   auto labelkv = trace::KeyValueIterableView<decltype(labels)>{labels};
   auto beta    = alpha.bindCounter(labelkv);
+  beta->add(1);
   beta->unbind();
 
   EXPECT_EQ(alpha.boundInstruments_[KvToString(labelkv)]->get_ref(), 0);
@@ -435,7 +436,34 @@ TEST(IntValueRecorder, StressRecord)
       125);  // count
 }
 
+TEST(Instruments, NoUpdateNoRecord)
+{
+  // This test verifies that instruments that have received no updates
+  // in the last collection period are not made into records for export.
+
+  Counter<int> alpha("alpha", "no description", "unitless", true);
+
+  std::map<std::string, std::string> labels = {{"key", "value"}};
+
+  auto labelkv = trace::KeyValueIterableView<decltype(labels)>{labels};
+
+  EXPECT_EQ(alpha.GetRecords().size(), 0);
+  alpha.add(1, labelkv);
+  EXPECT_EQ(alpha.GetRecords().size(), 1);
+
+  UpDownCounter<int> beta("beta", "no description", "unitless", true);
+
+  EXPECT_EQ(beta.GetRecords().size(), 0);
+  beta.add(1, labelkv);
+  EXPECT_EQ(beta.GetRecords().size(), 1);
+
+  ValueRecorder<int> gamma("gamma", "no description", "unitless", true);
+
+  EXPECT_EQ(gamma.GetRecords().size(), 0);
+  gamma.record(1, labelkv);
+  EXPECT_EQ(gamma.GetRecords().size(), 1);
+}
+
 }  // namespace metrics
 }  // namespace sdk
-
 OPENTELEMETRY_END_NAMESPACE