Optimize observability and metrics tags processing (#3902)

Both `KeyValues` and `Tags` unconditionally maintain the invariant that
they wrap distinct key-value pairs so the deduplication logic can be
removed. 
`Scannable#tagsDeduplicated` has been marked as deprecated.

benchmarks/build.gradle

@@ -13,18 +13,24 @@ configurations {
 dependencies {
   // Use the baseline to avoid using new APIs in the benchmarks
   compileOnly libs.reactor.perfBaseline.core
+  compileOnly libs.reactor.perfBaseline.coreMicrometer
   compileOnly libs.jsr305
 
   implementation "org.openjdk.jmh:jmh-core:$jmhVersion"
   implementation libs.reactor.perfBaseline.extra, {
     exclude group: 'io.projectreactor', module: 'reactor-core'
   }
+  implementation platform(libs.micrometer.bom)
   annotationProcessor "org.openjdk.jmh:jmh-generator-annprocess:$jmhVersion"
 
   current project(':reactor-core')
+  current project(':reactor-core-micrometer')
   baseline libs.reactor.perfBaseline.core, {
     changing = true
   }
+  baseline libs.reactor.perfBaseline.coreMicrometer, {
+    changing = true
+  }
 }
 
 task jmhProfilers(type: JavaExec, description:'Lists the available profilers for the jmh task', group: 'Development') {

benchmarks/src/main/java/reactor/core/observability/micrometer/MicrometerMeterListenerConfigurationResolveTagsBenchmark.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2024 VMware Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package reactor.core.observability.micrometer;
+
+import io.micrometer.core.instrument.Tags;
+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.Level;
+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.Warmup;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+
+@BenchmarkMode({Mode.AverageTime})
+@Warmup(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
+@Measurement(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS)
+@Fork(value = 1)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class MicrometerMeterListenerConfigurationResolveTagsBenchmark {
+	@Param({"1|1", "1|2", "1|5", "1|10", "2|2", "2|5", "2|10", "5|5", "5|10", "10|10"})
+	private String testCase;
+
+	private Publisher<Void> publisher;
+
+	@Setup(Level.Iteration)
+	public void setup() {
+		String[] arguments = testCase.split("\\|", -1);
+		int distinctTagCount = Integer.parseInt(arguments[0]);
+		int totalTagCount = Integer.parseInt(arguments[1]);
+
+		publisher = addTags(Mono.empty(), distinctTagCount, totalTagCount);
+	}
+
+	@SuppressWarnings("unused")
+	@Benchmark
+	public Tags measureThroughput() {
+		return MicrometerMeterListenerConfiguration.resolveTags(publisher, Tags.of("k", "v"));
+	}
+
+	private static <T> Mono<T> addTags(Mono<T> source, int distinct, int total) {
+		if (total == 0) {
+			return source;
+		}
+
+		return addTags(source.tag("k-" + total % distinct, "v-" + total), distinct, total - 1);
+	}
+}

gradle/libs.versions.toml

@@ -9,6 +9,7 @@
 # Baselines, should be updated on every release
 baseline-core-api = "3.7.0"
 baselinePerfCore = "3.7.0"
+baselinePerfCoreMicrometer = "1.2.0"
 baselinePerfExtra = "3.5.2"
 
 # Other shared versions
@@ -46,6 +47,7 @@ kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib", version.ref = "
 reactiveStreams = { module = "org.reactivestreams:reactive-streams", version.ref = "reactiveStreams" }
 reactiveStreams-tck = { module = "org.reactivestreams:reactive-streams-tck", version.ref = "reactiveStreams" }
 reactor-perfBaseline-core = { module = "io.projectreactor:reactor-core", version.ref = "baselinePerfCore" }
+reactor-perfBaseline-coreMicrometer = { module = "io.projectreactor:reactor-core-micrometer", version.ref = "baselinePerfCoreMicrometer" }
 reactor-perfBaseline-extra = { module = "io.projectreactor.addons:reactor-extra", version.ref = "baselinePerfExtra" }
 
 [plugins]

reactor-core-micrometer/src/main/java/reactor/core/observability/micrometer/MicrometerMeterListenerConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022 VMware Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2022-2024 VMware Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -93,9 +93,9 @@ static Tags resolveTags(Publisher<?> source, Tags tags) {
 		Scannable scannable = Scannable.from(source);
 
 		if (scannable.isScanAvailable()) {
-			List<Tag> discoveredTags = scannable.tagsDeduplicated()
-				.entrySet().stream()
-				.map(e -> Tag.of(e.getKey(), e.getValue()))
+			// `Tags#and` deduplicates tags by key, retaining the last value as required.
+			List<Tag> discoveredTags = scannable.tags()
+				.map(t -> Tag.of(t.getT1(), t.getT2()))
 				.collect(Collectors.toList());
 			return tags.and(discoveredTags);
 		}

reactor-core-micrometer/src/main/java/reactor/core/observability/micrometer/MicrometerObservationListenerConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022 VMware Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2022-2024 VMware Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -70,9 +70,9 @@ static KeyValues resolveKeyValues(Publisher<?> source, KeyValues tags) {
 		Scannable scannable = Scannable.from(source);
 
 		if (scannable.isScanAvailable()) {
-			List<KeyValue> discoveredTags = scannable.tagsDeduplicated()
-				.entrySet().stream()
-				.map(e -> KeyValue.of(e.getKey(), e.getValue()))
+			// `KeyValues#and` deduplicates tags by key, retaining the last value as required.
+			List<KeyValue> discoveredTags = scannable.tags()
+				.map(e -> KeyValue.of(e.getT1(), e.getT2()))
 				.collect(Collectors.toList());
 			return tags.and(discoveredTags);
 		}

reactor-core/src/main/java/reactor/core/Scannable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2023 VMware Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2017-2024 VMware Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -627,7 +627,9 @@ default Stream<Tuple2<String, String>> tags() {
 	 *
 	 * @return a {@link Map} of deduplicated tags from this {@link Scannable} and its reachable parents
 	 * @see #tags()
+	 * @deprecated Micrometer APIs generally deduplicate tags and key-value pairs by default, so for related use cases prefer {@link #tags()}.
 	 */
+	@Deprecated
 	default Map<String, String> tagsDeduplicated() {
 		return tags().collect(Collectors.toMap(Tuple2::getT1, Tuple2::getT2,
 			(s1, s2) -> s2, LinkedHashMap::new));

reactor-core/src/main/java/reactor/core/publisher/FluxMetrics.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2022 VMware Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2018-2024 VMware Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -295,9 +295,9 @@ static Tags resolveTags(Publisher<?> source, Tags tags) {
 		Scannable scannable = Scannable.from(source);
 
 		if (scannable.isScanAvailable()) {
-			List<Tag> discoveredTags = scannable.tagsDeduplicated()
-				.entrySet().stream()
-				.map(e -> Tag.of(e.getKey(), e.getValue()))
+			// `Tags#and` deduplicates tags by key, retaining the last value as required.
+			List<Tag> discoveredTags = scannable.tags()
+				.map(t -> Tag.of(t.getT1(), t.getT2()))
 				.collect(Collectors.toList());
 			return tags.and(discoveredTags);
 		}