Optimize Scannable#name() and related logic

benchmarks/src/main/java/reactor/core/publisher/MonoAllBenchmark.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.
@@ -49,8 +49,8 @@ public static void main(String[] args) throws Exception {
 
 	@SuppressWarnings("unused")
 	@Benchmark
-	public void measureThroughput() {
-		Flux.range(0, rangeSize)
+	public Boolean measureThroughput() {
+		return Flux.range(0, rangeSize)
 			.all(i -> i < Integer.MAX_VALUE)
 			.block();
 	}

benchmarks/src/main/java/reactor/core/publisher/MonoCallableBenchmark.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.
@@ -49,8 +49,8 @@ public static void main(String[] args) throws Exception {
 
 	@SuppressWarnings("unused")
 	@Benchmark
-	public void measureThroughput() {
-		Flux.range(0, rangeSize)
+	public Boolean measureThroughput() {
+		return Flux.range(0, rangeSize)
 			.all(i -> i < Integer.MAX_VALUE)
 			.block();
 	}

benchmarks/src/main/java/reactor/core/publisher/TracesBenchmark.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.publisher;
+
+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;
+
+@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 TracesBenchmark {
+	@Param({"0", "1", "2"})
+	private int reactorLeadingLines;
+
+	@Param({"0", "1", "2"})
+	private int trailingLines;
+
+	private String stackTrace;
+
+	@Setup(Level.Iteration)
+	public void setup() {
+		stackTrace = createStackTrace(reactorLeadingLines, trailingLines);
+	}
+
+	@SuppressWarnings("unused")
+	@Benchmark
+	public String measureThroughput() {
+		return Traces.extractOperatorAssemblyInformation(stackTrace);
+	}
+
+	private static String createStackTrace(int reactorLeadingLines, int trailingLines) {
+		StringBuilder sb = new StringBuilder();
+		for (int i = 0; i < reactorLeadingLines; i++) {
+			sb.append("\tat reactor.core.publisher.Flux.someOperation(Flux.java:42)\n");
+		}
+		sb.append("\tat some.user.package.SomeUserClass.someOperation(SomeUserClass.java:1234)\n");
+		for (int i = 0; i < trailingLines; i++) {
+			sb.append("\tat any.package.AnyClass.anyOperation(AnyClass.java:1)\n");
+		}
+		return sb.toString();
+	}
+}

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

@@ -449,7 +449,7 @@ default String name() {
 				.map(s -> s.scan(Attr.NAME))
 				.filter(Objects::nonNull)
 				.findFirst()
-				.orElse(stepName());
+				.orElseGet(this::stepName);
 	}
 
 	/**

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2023 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.
@@ -16,11 +16,10 @@
 
 package reactor.core.publisher;
 
-import java.util.List;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
-
+import reactor.util.annotation.Nullable;
 
 /**
  * Utilities around manipulating stack traces and displaying assembly traces.
@@ -29,6 +28,7 @@
  * @author Sergei Egorov
  */
 final class Traces {
+	private static final String PUBLISHER_PACKAGE_PREFIX = "reactor.core.publisher.";
 
 	/**
 	 * If set to true, the creation of FluxOnAssembly will capture the raw stacktrace
@@ -57,7 +57,6 @@ final class Traces {
 	static boolean shouldSanitize(String stackTraceRow) {
 		return stackTraceRow.startsWith("java.util.function")
 				|| stackTraceRow.startsWith("reactor.core.publisher.Mono.onAssembly")
-				|| stackTraceRow.equals("reactor.core.publisher.Mono.onAssembly")
 				|| stackTraceRow.equals("reactor.core.publisher.Flux.onAssembly")
 				|| stackTraceRow.equals("reactor.core.publisher.ParallelFlux.onAssembly")
 				|| stackTraceRow.startsWith("reactor.core.publisher.SignalLogger")
@@ -103,7 +102,7 @@ static String extractOperatorAssemblyInformation(String source) {
 	}
 
 	static boolean isUserCode(String line) {
-		return !line.startsWith("reactor.core.publisher") || line.contains("Test");
+		return !line.startsWith(PUBLISHER_PACKAGE_PREFIX) || line.contains("Test");
 	}
 
 	/**
@@ -129,48 +128,92 @@ static boolean isUserCode(String line) {
 	 * from the assembly stack trace.
 	 */
 	static String[] extractOperatorAssemblyInformationParts(String source) {
-		String[] uncleanTraces = source.split("\n");
-		final List<String> traces = Stream.of(uncleanTraces)
-		                                  .map(String::trim)
-		                                  .filter(s -> !s.isEmpty())
-		                                  .collect(Collectors.toList());
+		Iterator<String> traces = trimmedNonemptyLines(source);
 
-		if (traces.isEmpty()) {
+		if (!traces.hasNext()) {
 			return new String[0];
 		}
 
-		int i = 0;
-		while (i < traces.size() && !isUserCode(traces.get(i))) {
-			i++;
-		}
+		String prevLine = null;
+		String currentLine = traces.next();
 
-		String apiLine;
-		String userCodeLine;
-		if (i == 0) {
-			//no line was a reactor API line
-			apiLine = "";
-			userCodeLine = traces.get(0);
-		}
-		else if (i == traces.size()) {
-			//we skipped ALL lines, meaning they're all reactor API lines. We'll fully display the last one
-			apiLine = "";
-			userCodeLine = traces.get(i-1).replaceFirst("reactor.core.publisher.", "");
-		}
-		else {
-			//currently on user code line, previous one is API
-			apiLine = traces.get(i - 1);
-			userCodeLine = traces.get(i);
+		if (isUserCode(currentLine)) {
+			// No line is a Reactor API line.
+			return new String[]{currentLine};
 		}
 
-		//now we want something in the form "Flux.map ⇢ user.code.Class.method(Class.java:123)"
-		if (apiLine.isEmpty()) return new String[] { userCodeLine };
+		while (traces.hasNext()) {
+			prevLine = currentLine;
+			currentLine = traces.next();
+
+			if (isUserCode(currentLine)) {
+				// Currently on user code line, previous one is API. Attempt to create something in the form
+				// "Flux.map ⇢ user.code.Class.method(Class.java:123)".
+				int linePartIndex = prevLine.indexOf('(');
+				String apiLine = linePartIndex > 0 ?
+					prevLine.substring(0, linePartIndex) :
+					prevLine;
 
-		int linePartIndex = apiLine.indexOf('(');
-		if (linePartIndex > 0) {
-			apiLine = apiLine.substring(0, linePartIndex);
+				return new String[]{dropPublisherPackagePrefix(apiLine), "at " + currentLine};
+			}
 		}
-		apiLine = apiLine.replaceFirst("reactor.core.publisher.", "");
 
-		return new String[] { apiLine, "at " + userCodeLine };
+		// We skipped ALL lines, meaning they're all Reactor API lines. We'll fully display the last
+		// one.
+		return new String[]{dropPublisherPackagePrefix(currentLine)};
+	}
+
+	private static String dropPublisherPackagePrefix(String line) {
+		return line.startsWith(PUBLISHER_PACKAGE_PREFIX)
+			? line.substring(PUBLISHER_PACKAGE_PREFIX.length())
+			: line;
+	}
+
+	/**
+	 * Returns an iterator over all trimmed non-empty lines in the given source string.
+	 *
+	 * @implNote This implementation attempts to minimize allocations.
+	 */
+	private static Iterator<String> trimmedNonemptyLines(String source) {
+		return new Iterator<String>() {
+			private int index = 0;
+			@Nullable
+			private String next = getNextLine();
+
+			@Override
+			public boolean hasNext() {
+				return next != null;
+			}
+
+			@Override
+			public String next() {
+				String current = next;
+				if (current == null) {
+					throw new NoSuchElementException();
+				}
+				next = getNextLine();
+				return current;
+			}
+
+			@Nullable
+			private String getNextLine() {
+				if (index >= source.length()) {
+					return null;
+				}
+
+				while (index < source.length()) {
+					int end = source.indexOf('\n', index);
+					if (end == -1) {
+						end = source.length();
+					}
+					String line = source.substring(index, end).trim();
+					index = end + 1;
+					if (!line.isEmpty()) {
+						return line;
+					}
+				}
+				return null;
+			}
+		};
 	}
 }