Merge pull request #290 from Metaswitch/histogram-observe-multiple

Allow more than one histogram observation at a time

core/include/prometheus/histogram.h

@@ -31,7 +31,7 @@ class Histogram {
 
   static const MetricType metric_type{MetricType::Histogram};
 
-  /// \brief Create a histogram with manually choosen buckets.
+  /// \brief Create a histogram with manually chosen buckets.
   ///
   /// The BucketBoundaries are a list of monotonically increasing values
   /// representing the bucket boundaries. Each consecutive pair of values is
@@ -51,6 +51,14 @@ class Histogram {
   /// sum of all observations is incremented.
   void Observe(double value);
 
+  /// \brief Observe multiple data points.
+  ///
+  /// Increments counters given a count for each bucket. (i.e. the caller of
+  /// this function must have already sorted the values into buckets).
+  /// Also increments the total sum of all observations by the given value.
+  void ObserveMultiple(const std::vector<double> bucket_increments,
+                       const double sum_of_values);
+
   /// \brief Get the current value of the counter.
   ///
   /// Collect is called by the Registry when collecting metrics.

core/src/histogram.cc

@@ -24,6 +24,15 @@ void Histogram::Observe(const double value) {
   bucket_counts_[bucket_index].Increment();
 }
 
+void Histogram::ObserveMultiple(const std::vector<double> bucket_increments,
+                                const double sum_of_values) {
+  sum_.Increment(sum_of_values);
+
+  for (std::size_t i{0}; i < bucket_counts_.size(); ++i) {
+    { bucket_counts_[i].Increment(bucket_increments[i]); }
+  }
+}
+
 ClientMetric Histogram::Collect() const {
   auto metric = ClientMetric{};
 

core/tests/histogram_test.cc

@@ -79,5 +79,27 @@ TEST(HistogramTest, cumulative_bucket_count) {
   EXPECT_EQ(h.bucket.at(2).cumulative_count, 7U);
 }
 
+TEST(HistogramTest, observe_multiple_test_bucket_counts) {
+  Histogram histogram{{1, 2}};
+  histogram.ObserveMultiple({5, 9, 3}, 20);
+  histogram.ObserveMultiple({0, 20, 6}, 34);
+  auto metric = histogram.Collect();
+  auto h = metric.histogram;
+  ASSERT_EQ(h.bucket.size(), 3U);
+  EXPECT_EQ(h.bucket.at(0).cumulative_count, 5U);
+  EXPECT_EQ(h.bucket.at(1).cumulative_count, 34U);
+  EXPECT_EQ(h.bucket.at(2).cumulative_count, 43U);
+}
+
+TEST(HistogramTest, observe_multiple_test_total_sum) {
+  Histogram histogram{{1, 2}};
+  histogram.ObserveMultiple({5, 9, 3}, 20);
+  histogram.ObserveMultiple({0, 20, 6}, 34);
+  auto metric = histogram.Collect();
+  auto h = metric.histogram;
+  EXPECT_EQ(h.sample_count, 43U);
+  EXPECT_EQ(h.sample_sum, 54);
+}
+
 }  // namespace
 }  // namespace prometheus