Histogram Aggregation - core SDK implementation

exporters/otlp/common/src/main/java/io/opentelemetry/exporter/otlp/internal/MetricAdapter.java

@@ -149,6 +149,9 @@ static Metric toProtoMetric(MetricData metricData) {
                 .addAllDataPoints(toDoubleDataPoints(doubleGaugeData.getPoints()))
                 .build());
         break;
+      case HISTOGRAM:
+        // TODO: no-op, will add in the following PRs
+        break;
     }
     return builder.build();
   }

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/MetricAdapter.java

@@ -85,6 +85,8 @@ static Collector.Type toMetricFamilyType(MetricData metricData) {
         return Collector.Type.GAUGE;
       case SUMMARY:
         return Collector.Type.SUMMARY;
+      case HISTOGRAM:
+        return Collector.Type.HISTOGRAM;
     }
     return Collector.Type.UNKNOWN;
   }
@@ -122,6 +124,9 @@ static List<Sample> toSamples(
           addSummarySamples(
               (DoubleSummaryPointData) pointData, name, labelNames, labelValues, samples);
           break;
+        case HISTOGRAM:
+          // TODO: no-op, will add in the following PRs
+          break;
       }
     }
     return samples;
@@ -189,6 +194,8 @@ private static Collection<? extends PointData> getPoints(MetricData metricData)
         return metricData.getLongSumData().getPoints();
       case SUMMARY:
         return metricData.getDoubleSummaryData().getPoints();
+      case HISTOGRAM:
+        return metricData.getDoubleHistogramData().getPoints();
     }
     return Collections.emptyList();
   }

sdk/metrics/src/jmh/java/io/opentelemetry/sdk/metrics/aggregator/DoubleHistogramBenchmark.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.aggregator;
+
+import io.opentelemetry.sdk.common.InstrumentationLibraryInfo;
+import io.opentelemetry.sdk.metrics.common.InstrumentDescriptor;
+import io.opentelemetry.sdk.metrics.common.InstrumentType;
+import io.opentelemetry.sdk.metrics.common.InstrumentValueType;
+import io.opentelemetry.sdk.resources.Resource;
+import java.util.concurrent.TimeUnit;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+@State(Scope.Benchmark)
+public class DoubleHistogramBenchmark {
+  private static final Aggregator<HistogramAccumulation> aggregator =
+      AggregatorFactory.histogram(new double[] {10, 100, 1_000}, /* stateful= */ false)
+          .create(
+              Resource.getDefault(),
+              InstrumentationLibraryInfo.empty(),
+              InstrumentDescriptor.create(
+                  "name",
+                  "description",
+                  "1",
+                  InstrumentType.VALUE_RECORDER,
+                  InstrumentValueType.DOUBLE));
+  private AggregatorHandle<HistogramAccumulation> aggregatorHandle;
+
+  @Setup(Level.Trial)
+  public final void setup() {
+    aggregatorHandle = aggregator.createHandle();
+  }
+
+  @Benchmark
+  @Fork(1)
+  @Warmup(iterations = 5, time = 1)
+  @Measurement(iterations = 10, time = 1)
+  @OutputTimeUnit(TimeUnit.MILLISECONDS)
+  @Threads(value = 10)
+  public void aggregate_10Threads() {
+    aggregatorHandle.recordDouble(100.0056);
+  }
+
+  @Benchmark
+  @Fork(1)
+  @Warmup(iterations = 5, time = 1)
+  @Measurement(iterations = 10, time = 1)
+  @OutputTimeUnit(TimeUnit.MILLISECONDS)
+  @Threads(value = 5)
+  public void aggregate_5Threads() {
+    aggregatorHandle.recordDouble(100.0056);
+  }
+
+  @Benchmark
+  @Fork(1)
+  @Warmup(iterations = 5, time = 1)
+  @Measurement(iterations = 10, time = 1)
+  @OutputTimeUnit(TimeUnit.MILLISECONDS)
+  @Threads(value = 1)
+  public void aggregate_1Threads() {
+    aggregatorHandle.recordDouble(100.0056);
+  }
+}

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/aggregator/AggregatorFactory.java

@@ -45,6 +45,18 @@ static AggregatorFactory count(AggregationTemporality temporality) {
     return new CountAggregatorFactory(temporality);
   }
 
+  /**
+   * Returns an {@code AggregatorFactory} that calculates an approximation of the distribution of
+   * the measurements taken.
+   *
+   * @param stateful configures if the aggregator is stateful.
+   * @param boundaries configures the fixed bucket boundaries.
+   * @return an {@code AggregationFactory} that calculates histogram of recorded measurements.
+   */
+  static AggregatorFactory histogram(double[] boundaries, boolean stateful) {
+    return new HistogramAggregatorFactory(boundaries, stateful);
+  }
+
   /**
    * Returns an {@code AggregationFactory} that calculates the last value of all recorded
    * measurements.

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/aggregator/DoubleHistogramAggregator.java

@@ -0,0 +1,168 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.aggregator;
+
+import io.opentelemetry.api.metrics.common.Labels;
+import io.opentelemetry.sdk.common.InstrumentationLibraryInfo;
+import io.opentelemetry.sdk.metrics.common.InstrumentDescriptor;
+import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
+import io.opentelemetry.sdk.metrics.data.DoubleHistogramData;
+import io.opentelemetry.sdk.metrics.data.MetricData;
+import io.opentelemetry.sdk.resources.Resource;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
+import javax.annotation.concurrent.GuardedBy;
+
+final class DoubleHistogramAggregator extends AbstractAggregator<HistogramAccumulation> {
+  private final ImmutableDoubleArray boundaries;
+
+  DoubleHistogramAggregator(
+      Resource resource,
+      InstrumentationLibraryInfo instrumentationLibraryInfo,
+      InstrumentDescriptor instrumentDescriptor,
+      ImmutableDoubleArray boundaries,
+      boolean stateful) {
+    super(resource, instrumentationLibraryInfo, instrumentDescriptor, stateful);
+    this.boundaries = boundaries;
+  }
+
+  @Override
+  public AggregatorHandle<HistogramAccumulation> createHandle() {
+    return new Handle(this.boundaries);
+  }
+
+  /**
+   * Return the result of the merge of two histogram accumulations. As long as one Aggregator
+   * instance produces all Accumulations with constant boundaries we don't need to worry about
+   * merging accumulations with different boundaries.
+   */
+  @Override
+  public final HistogramAccumulation merge(HistogramAccumulation x, HistogramAccumulation y) {
+    long[] mergedCounts = new long[x.getCounts().length()];
+    for (int i = 0; i < x.getCounts().length(); ++i) {
+      mergedCounts[i] = x.getCounts().get(i) + y.getCounts().get(i);
+    }
+    return HistogramAccumulation.create(
+        x.getCount() + y.getCount(),
+        x.getSum() + y.getSum(),
+        ImmutableLongArray.copyOf(mergedCounts));
+  }
+
+  @Override
+  public final MetricData toMetricData(
+      Map<Labels, HistogramAccumulation> accumulationByLabels,
+      long startEpochNanos,
+      long lastCollectionEpoch,
+      long epochNanos) {
+    return MetricData.createDoubleHistogram(
+        getResource(),
+        getInstrumentationLibraryInfo(),
+        getInstrumentDescriptor().getName(),
+        getInstrumentDescriptor().getDescription(),
+        getInstrumentDescriptor().getUnit(),
+        DoubleHistogramData.create(
+            isStateful() ? AggregationTemporality.CUMULATIVE : AggregationTemporality.DELTA,
+            MetricDataUtils.toDoubleHistogramPointList(
+                accumulationByLabels,
+                isStateful() ? startEpochNanos : lastCollectionEpoch,
+                epochNanos,
+                boundaries.toList())));
+  }
+
+  @Override
+  public HistogramAccumulation accumulateDouble(double value) {
+    return HistogramAccumulation.create(1, value, ImmutableLongArray.of(1));
+  }
+
+  @Override
+  public HistogramAccumulation accumulateLong(long value) {
+    return HistogramAccumulation.create(1, value, ImmutableLongArray.of(1));
+  }
+
+  static final class Handle extends AggregatorHandle<HistogramAccumulation> {
+    private final ImmutableDoubleArray boundaries;
+
+    private final ReentrantLock lock = new ReentrantLock();
+
+    @GuardedBy("lock")
+    private final State current;
+
+    Handle(ImmutableDoubleArray boundaries) {
+      this.boundaries = boundaries;
+      this.current = new State(this.boundaries.length() + 1);
+    }
+
+    // Benchmark shows that linear search performs better than binary search with ordinary
+    // buckets.
+    private int findBucketIndex(double value) {
+      for (int i = 0; i < boundaries.length(); ++i) {
+        if (value < boundaries.get(i)) {
+          return i;
+        }
+      }
+      return boundaries.length();
+    }
+
+    @Override
+    protected HistogramAccumulation doAccumulateThenReset() {
+      double sum;
+      ImmutableLongArray counts;
+      lock.lock();
+      try {
+        sum = current.sum;
+        counts = ImmutableLongArray.copyOf(current.counts);
+        current.reset();
+      } finally {
+        lock.unlock();
+      }
+
+      long totalCount = 0;
+      for (int i = 0; i < counts.length(); ++i) {
+        totalCount += counts.get(i);
+      }
+
+      return HistogramAccumulation.create(totalCount, sum, counts);
+    }
+
+    @Override
+    protected void doRecordDouble(double value) {
+      int bucketIndex = findBucketIndex(value);
+
+      lock.lock();
+      try {
+        current.record(bucketIndex, value);
+      } finally {
+        lock.unlock();
+      }
+    }
+
+    @Override
+    protected void doRecordLong(long value) {
+      doRecordDouble((double) value);
+    }
+
+    private static final class State {
+      private double sum;
+      private final long[] counts;
+
+      public State(int bucketSize) {
+        this.counts = new long[bucketSize];
+        reset();
+      }
+
+      private void reset() {
+        this.sum = 0;
+        Arrays.fill(this.counts, 0);
+      }
+
+      private void record(int bucketIndex, double value) {
+        this.sum += value;
+        this.counts[bucketIndex]++;
+      }
+    }
+  }
+}

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/aggregator/HistogramAccumulation.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.aggregator;
+
+import com.google.auto.value.AutoValue;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@AutoValue
+abstract class HistogramAccumulation {
+  /**
+   * Creates a new {@link HistogramAccumulation} with the given values.
+   *
+   * @return a new {@link HistogramAccumulation} with the given values.
+   */
+  static HistogramAccumulation create(long count, double sum, ImmutableLongArray counts) {
+    return new AutoValue_HistogramAccumulation(count, sum, counts);
+  }
+
+  HistogramAccumulation() {}
+
+  /**
+   * The number of measurements taken.
+   *
+   * @return the count of recorded measurements.
+   */
+  abstract long getCount();
+
+  /**
+   * The sum of all measurements recorded.
+   *
+   * @return the sum of recorded measurements.
+   */
+  abstract double getSum();
+
+  /**
+   * The counts in each bucket.
+   *
+   * @return the counts in each bucket.
+   */
+  abstract ImmutableLongArray getCounts();
+}