Memory Mode support: Adding memory mode, and implementing it for Asynchronous Instruments

CONTRIBUTING.md

@@ -8,7 +8,7 @@ requirements and recommendations.
 
 If you want to add new features or change behavior, please make sure your changes follow the
 [OpenTelemetry Specification](https://github.com/open-telemetry/opentelemetry-specification).
-Otherwise file an issue or submit a PR to the specification repo first.
+Otherwise, file an issue or submit a PR to the specification repo first.
 
 Make sure to review the projects [license](LICENSE) and sign the
 [CNCF CLA](https://identity.linuxfoundation.org/projects/cncf). A signed CLA will be enforced by an
@@ -52,7 +52,8 @@ $ ./gradlew check
 
 Note: this gradle task will potentially generate changes to files in
 the `docs/apidiffs/current_vs_latest`
-directory. Please make sure to include any changes to these files in your pull request.
+directory. Please make sure to include any changes to these files in your pull request (i.e.
+add those files to your commits in the PR).
 
 ## PR Review
 

dependencyManagement/build.gradle.kts

@@ -45,6 +45,7 @@ val DEPENDENCIES = listOf(
   "io.opencensus:opencensus-contrib-exemplar-util:${opencensusVersion}",
   "org.openjdk.jmh:jmh-core:${jmhVersion}",
   "org.openjdk.jmh:jmh-generator-bytecode:${jmhVersion}",
+  "org.openjdk.jmh:jmh-generator-annprocess:${jmhVersion}",
   "org.mockito:mockito-core:${mockitoVersion}",
   "org.mockito:mockito-junit-jupiter:${mockitoVersion}",
   "org.slf4j:slf4j-simple:${slf4jVersion}",

docs/apidiffs/current_vs_latest/opentelemetry-sdk-common.txt

@@ -1,2 +1,11 @@
 Comparing source compatibility of  against 
-No changes.
++++  NEW ENUM: PUBLIC(+) FINAL(+) io.opentelemetry.sdk.common.export.MemoryMode  (compatible)
+	+++  CLASS FILE FORMAT VERSION: 52.0 <- n.a.
+	+++  NEW INTERFACE: java.lang.constant.Constable
+	+++  NEW INTERFACE: java.lang.Comparable
+	+++  NEW INTERFACE: java.io.Serializable
+	+++  NEW SUPERCLASS: java.lang.Enum
+	+++  NEW FIELD: PUBLIC(+) STATIC(+) FINAL(+) io.opentelemetry.sdk.common.export.MemoryMode REUSABLE_DATA
+	+++  NEW FIELD: PUBLIC(+) STATIC(+) FINAL(+) io.opentelemetry.sdk.common.export.MemoryMode IMMUTABLE_DATA
+	+++  NEW METHOD: PUBLIC(+) STATIC(+) io.opentelemetry.sdk.common.export.MemoryMode valueOf(java.lang.String)
+	+++  NEW METHOD: PUBLIC(+) STATIC(+) io.opentelemetry.sdk.common.export.MemoryMode[] values()

docs/apidiffs/current_vs_latest/opentelemetry-sdk-metrics.txt

@@ -1,2 +1,10 @@
 Comparing source compatibility of  against 
-No changes.
+***  MODIFIED INTERFACE: PUBLIC ABSTRACT io.opentelemetry.sdk.metrics.export.MetricExporter  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.common.export.MemoryMode getMemoryMode()
+***  MODIFIED INTERFACE: PUBLIC ABSTRACT io.opentelemetry.sdk.metrics.export.MetricReader  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.common.export.MemoryMode getMemoryMode()
+***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.sdk.metrics.export.PeriodicMetricReader  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.common.export.MemoryMode getMemoryMode()

docs/apidiffs/current_vs_latest/opentelemetry-sdk-testing.txt

@@ -1,2 +1,12 @@
 Comparing source compatibility of  against 
-No changes.
+***  MODIFIED CLASS: PUBLIC io.opentelemetry.sdk.testing.exporter.InMemoryMetricReader  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) STATIC(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReaderBuilder builder()
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.common.export.MemoryMode getMemoryMode()
++++  NEW CLASS: PUBLIC(+) FINAL(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReaderBuilder  (not serializable)
+	+++  CLASS FILE FORMAT VERSION: 52.0 <- n.a.
+	+++  NEW SUPERCLASS: java.lang.Object
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReader build()
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReaderBuilder setAggregationTemporalitySelector(io.opentelemetry.sdk.metrics.export.AggregationTemporalitySelector)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReaderBuilder setDefaultAggregationSelector(io.opentelemetry.sdk.metrics.export.DefaultAggregationSelector)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.sdk.testing.exporter.InMemoryMetricReaderBuilder setMemoryMode(io.opentelemetry.sdk.common.export.MemoryMode)

sdk/common/src/main/java/io/opentelemetry/sdk/common/export/MemoryMode.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.common.export;
+
+/** The memory semantics of the SDK. */
+public enum MemoryMode {
+
+  /**
+   * Reuses objects to reduce allocations.
+   *
+   * <p>In this mode, the SDK reuses objects to reduce allocations, at the expense of disallowing
+   * concurrent collections / exports.
+   */
+  REUSABLE_DATA,
+
+  /**
+   * Uses immutable data structures.
+   *
+   * <p>In this mode, the SDK passes immutable objects to exporters / readers, increasing
+   * allocations but ensuring safe concurrent exports.
+   */
+  IMMUTABLE_DATA
+}

sdk/metrics/build.gradle.kts

@@ -41,6 +41,13 @@ testing {
         }
       }
     }
+    register<JvmTestSuite>("jmhBasedTest") {
+      dependencies {
+        implementation("org.openjdk.jmh:jmh-core")
+        implementation("org.openjdk.jmh:jmh-generator-bytecode")
+        annotationProcessor("org.openjdk.jmh:jmh-generator-annprocess")
+      }
+    }
   }
 }
 

sdk/metrics/src/jmhBasedTest/java/io/opentelemetry/sdk/metrics/internal/state/AsynchronousMetricStorageGarbageCollectionBenchmark.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.state;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.sdk.common.export.MemoryMode;
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.SdkMeterProviderBuilder;
+import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
+import io.opentelemetry.sdk.metrics.internal.exemplar.ExemplarFilter;
+import java.time.Duration;
+import java.util.List;
+import java.util.Random;
+import java.util.concurrent.TimeUnit;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.TearDown;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+/**
+ * Run this through {@link AsynchronousMetricStorageGarbageCollectionBenchmarkTest}, as it runs it
+ * embedded with the GC profiler which what this test designed for (No need for command line run)
+ *
+ * <p>This test creates 10 asynchronous counters (any asynchronous instrument will do as the code
+ * path is almost the same for all async instrument types), and 1000 attribute sets. Each time the
+ * test runs, it calls `flush` which effectively calls the callback for each counter. Each such
+ * callback records a random number for each of the 1000 attribute sets. The result list ends up in
+ * {@link NoopMetricExporter} which does nothing with it.
+ *
+ * <p>This is repeated 100 times, collectively called Operation in the statistics and each such
+ * operation is repeated 20 times - known as Iteration.
+ *
+ * <p>Each such test is repeated, with a brand new JVM, for all combinations of {@link MemoryMode}
+ * and {@link AggregationTemporality}. This is done since each combination has a different code
+ * path.
+ */
+@BenchmarkMode(Mode.SingleShotTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Measurement(iterations = 20, batchSize = 100)
+@Warmup(iterations = 10, batchSize = 10)
+@Fork(1)
+public class AsynchronousMetricStorageGarbageCollectionBenchmark {
+
+  @State(value = Scope.Benchmark)
+  @SuppressWarnings("SystemOut")
+  public static class ThreadState {
+    private final int cardinality;
+    private final int countersCount;
+    @Param public AggregationTemporality aggregationTemporality;
+    @Param public MemoryMode memoryMode;
+    SdkMeterProvider sdkMeterProvider;
+    private final Random random = new Random();
+    List<Attributes> attributesList;
+
+    /** Creates a ThreadState. */
+    @SuppressWarnings("unused")
+    public ThreadState() {
+      cardinality = 1000;
+      countersCount = 10;
+    }
+
+    @SuppressWarnings("SpellCheckingInspection")
+    @Setup
+    public void setup() {
+      PeriodicMetricReader metricReader =
+          PeriodicMetricReader.builder(
+                  // Configure an exporter that configures the temporality and aggregation
+                  // for the test case, but otherwise drops the data on export
+                  new NoopMetricExporter(aggregationTemporality, Aggregation.sum(), memoryMode))
+              // Effectively disable periodic reading so reading is only done on #flush()
+              .setInterval(Duration.ofSeconds(Integer.MAX_VALUE))
+              .build();
+      SdkMeterProviderBuilder builder = SdkMeterProvider.builder();
+      SdkMeterProviderUtil.registerMetricReaderWithCardinalitySelector(
+          builder, metricReader, unused -> cardinality + 1);
+
+      attributesList = AttributesGenerator.generate(cardinality);
+
+      // Disable examplars
+      SdkMeterProviderUtil.setExemplarFilter(builder, ExemplarFilter.alwaysOff());
+
+      sdkMeterProvider = builder.build();
+      for (int i = 0; i < countersCount; i++) {
+        sdkMeterProvider
+            .get("meter")
+            .counterBuilder("counter" + i)
+            .buildWithCallback(
+                observableLongMeasurement -> {
+                  for (int j = 0; j < attributesList.size(); j++) {
+                    Attributes attributes = attributesList.get(j);
+                    observableLongMeasurement.record(random.nextInt(10_000), attributes);
+                  }
+                });
+      }
+    }
+
+    @TearDown
+    public void tearDown() {
+      sdkMeterProvider.shutdown().join(10, TimeUnit.SECONDS);
+    }
+  }
+
+  /**
+   * Collects all asynchronous instruments metric data.
+   *
+   * @param threadState thread-state
+   */
+  @Benchmark
+  @Threads(value = 1)
+  public void recordAndCollect(ThreadState threadState) {
+    threadState.sdkMeterProvider.forceFlush().join(10, TimeUnit.SECONDS);
+  }
+}

sdk/metrics/src/jmhBasedTest/java/io/opentelemetry/sdk/metrics/internal/state/AsynchronousMetricStorageGarbageCollectionBenchmarkTest.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.state;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.opentelemetry.sdk.common.InstrumentationScopeInfo;
+import io.opentelemetry.sdk.common.export.MemoryMode;
+import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
+import io.opentelemetry.sdk.resources.Resource;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import org.assertj.core.data.Offset;
+import org.junit.jupiter.api.Assumptions;
+import org.junit.jupiter.api.Test;
+import org.openjdk.jmh.infra.BenchmarkParams;
+import org.openjdk.jmh.results.BenchmarkResult;
+import org.openjdk.jmh.results.Result;
+import org.openjdk.jmh.results.RunResult;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+public class AsynchronousMetricStorageGarbageCollectionBenchmarkTest {
+
+  /**
+   * This test validates that in {@link MemoryMode#REUSABLE_DATA}, {@link
+   * AsynchronousMetricStorage#collect(Resource, InstrumentationScopeInfo, long, long)} barely
+   * allocates memory which is then subsequently garbage collected. It is done so comparatively to
+   * {@link MemoryMode#IMMUTABLE_DATA},
+   *
+   * <p>It runs the JMH test {@link AsynchronousMetricStorageGarbageCollectionBenchmark} with GC
+   * profiler, and measures for each parameter combination the garbage collector normalized rate
+   * (bytes allocated per Operation).
+   *
+   * <p>Memory allocations can be hidden even at an innocent foreach loop on a collection, which
+   * under the hood allocates an internal object O(N) times. Someone can accidentally refactor such
+   * loop, resulting in 30% increase of garbage collected objects during a single collect() run.
+   */
+  @SuppressWarnings("rawtypes")
+  @Test
+  public void normalizedAllocationRateTest() throws RunnerException {
+    // GitHub CI has an environment variable (CI=true). We can use it to skip
+    // this test since it's a lengthy one (roughly 10 seconds) and have it running
+    // only in GitHub CI
+    Assumptions.assumeTrue(
+        "true".equals(System.getenv("CI")),
+        "This test should only run in GitHub CI since it's long");
+
+    // Runs AsynchronousMetricStorageMemoryProfilingBenchmark
+    // with garbage collection profiler
+    Options opt =
+        new OptionsBuilder()
+            .include(AsynchronousMetricStorageGarbageCollectionBenchmark.class.getSimpleName())
+            .addProfiler("gc")
+            .shouldFailOnError(true)
+            .jvmArgs("-Xmx1500m")
+            .build();
+    Collection<RunResult> results = new Runner(opt).run();
+
+    // Collect the normalized GC allocation rate per parameters combination
+    Map<String, Map<String, Double>> resultMap = new HashMap<>();
+    for (RunResult result : results) {
+      for (BenchmarkResult benchmarkResult : result.getBenchmarkResults()) {
+        BenchmarkParams benchmarkParams = benchmarkResult.getParams();
+
+        String memoryMode = benchmarkParams.getParam("memoryMode");
+        String aggregationTemporality = benchmarkParams.getParam("aggregationTemporality");
+        assertThat(memoryMode).isNotNull();
+        assertThat(aggregationTemporality).isNotNull();
+
+        Map<String, Result> secondaryResults = benchmarkResult.getSecondaryResults();
+        Result allocRateNorm = secondaryResults.get("gc.alloc.rate.norm");
+        assertThat(allocRateNorm)
+            .describedAs("Allocation rate in secondary results: %s", secondaryResults)
+            .isNotNull();
+
+        resultMap
+            .computeIfAbsent(aggregationTemporality, k -> new HashMap<>())
+            .put(memoryMode, allocRateNorm.getScore());
+      }
+    }
+
+    assertThat(resultMap).hasSameSizeAs(AggregationTemporality.values());
+
+    // Asserts that reusable data GC allocation rate is a tiny fraction of immutable data
+    // GC allocation rate
+    resultMap.forEach(
+        (aggregationTemporality, memoryModeToAllocRateMap) -> {
+          Double immutableDataAllocRate =
+              memoryModeToAllocRateMap.get(MemoryMode.IMMUTABLE_DATA.toString());
+          Double reusableDataAllocRate =
+              memoryModeToAllocRateMap.get(MemoryMode.REUSABLE_DATA.toString());
+
+          assertThat(immutableDataAllocRate).isNotNull().isNotZero();
+          assertThat(reusableDataAllocRate).isNotNull().isNotZero();
+          assertThat(100 - (reusableDataAllocRate / immutableDataAllocRate) * 100)
+              .isCloseTo(99.8, Offset.offset(2.0));
+        });
+  }
+}

sdk/metrics/src/jmhBasedTest/java/io/opentelemetry/sdk/metrics/internal/state/AttributesGenerator.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.state;
+
+import io.opentelemetry.api.common.Attributes;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Random;
+
+public class AttributesGenerator {
+
+  private AttributesGenerator() {}
+
+  /**
+   * Generates a list of unique attributes, with a single attribute key, and random value.
+   *
+   * @param uniqueAttributesCount The amount of unique attribute sets to generate
+   * @return The list of generates {@link Attributes}
+   */
+  public static List<Attributes> generate(int uniqueAttributesCount) {
+    Random random = new Random();
+    HashSet<String> attributeSet = new HashSet<>();
+    ArrayList<Attributes> attributesList = new ArrayList<>(uniqueAttributesCount);
+    String last = "aaaaaaaaaaaaaaaaaaaaaaaaaa";
+    for (int i = 0; i < uniqueAttributesCount; i++) {
+      char[] chars = last.toCharArray();
+      int attempts = 0;
+      do {
+        chars[random.nextInt(last.length())] = (char) (random.nextInt(26) + 'a');
+      } while (attributeSet.contains(new String(chars)) && ++attempts < 1000);
+      if (attributeSet.contains(new String(chars))) {
+        throw new IllegalStateException("Couldn't create new random attributes");
+      }
+      last = new String(chars);
+      attributesList.add(Attributes.builder().put("key", last).build());
+      attributeSet.add(last);
+    }
+
+    return attributesList;
+  }
+}