Move performance test to JMH benchmark

This commit removes an ignored performance test in the
`ConcurrentReferenceHashMap` test suite and converts it to a JMH
benchmark.

spring-core/src/jmh/java/org/springframework/util/ConcurrentReferenceHashMapBenchmark.java

@@ -0,0 +1,118 @@
+/*
+ * Copyright 2002-2023 the original author or authors.
+ *
+ * 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 org.springframework.util;
+
+
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.WeakHashMap;
+import java.util.function.Function;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Mode;
+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.infra.Blackhole;
+
+/**
+ * Benchmarks for {@link ConcurrentReferenceHashMap}.
+ * <p>This benchmark ensures that {@link ConcurrentReferenceHashMap} performs
+ * better than {@link java.util.Collections#synchronizedMap(Map)} with
+ * concurrent read operations.
+ * <p>Typically this can be run with {@code "java -jar spring-core-jmh.jar -t 30 -f 2 ConcurrentReferenceHashMapBenchmark"}.
+ * @author Brian Clozel
+ */
+@BenchmarkMode(Mode.Throughput)
+public class ConcurrentReferenceHashMapBenchmark {
+
+	@Benchmark
+	public void concurrentMap(ConcurrentMapBenchmarkData data, Blackhole bh) {
+		for (String element : data.elements) {
+			WeakReference<String> value = data.map.get(element);
+			bh.consume(value);
+		}
+	}
+
+	@State(Scope.Benchmark)
+	public static class ConcurrentMapBenchmarkData {
+
+		@Param({"500"})
+		public int capacity;
+		private final Function<String, String> generator = key -> key + "value";
+
+		public List<String> elements;
+
+		public Map<String, WeakReference<String>> map;
+
+		@Setup(Level.Iteration)
+		public void setup() {
+			this.elements = new ArrayList<>(this.capacity);
+			this.map = new ConcurrentReferenceHashMap<>();
+			Random random = new Random();
+			random.ints(this.capacity).forEach(value -> {
+				String element = String.valueOf(value);
+				this.elements.add(element);
+				this.map.put(element, new WeakReference<>(this.generator.apply(element)));
+			});
+			this.elements.sort(String::compareTo);
+		}
+	}
+
+	@Benchmark
+	public void synchronizedMap(SynchronizedMapBenchmarkData data, Blackhole bh) {
+		for (String element : data.elements) {
+			WeakReference<String> value = data.map.get(element);
+			bh.consume(value);
+		}
+	}
+
+	@State(Scope.Benchmark)
+	public static class SynchronizedMapBenchmarkData {
+
+		@Param({"500"})
+		public int capacity;
+
+		private Function<String, String> generator = key -> key + "value";
+
+		public List<String> elements;
+
+		public Map<String, WeakReference<String>> map;
+
+
+		@Setup(Level.Iteration)
+		public void setup() {
+			this.elements = new ArrayList<>(this.capacity);
+			this.map = Collections.synchronizedMap(new WeakHashMap<>());
+			Random random = new Random();
+			random.ints(this.capacity).forEach(value -> {
+				String element = String.valueOf(value);
+				this.elements.add(element);
+				this.map.put(element, new WeakReference<>(this.generator.apply(element)));
+			});
+			this.elements.sort(String::compareTo);
+		}
+	}
+
+}

spring-core/src/test/java/org/springframework/util/ConcurrentReferenceHashMapTests.java

@@ -16,9 +16,7 @@
 
 package org.springframework.util;
 
-import java.lang.ref.WeakReference;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -27,9 +25,7 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.WeakHashMap;
 
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.lang.Nullable;
@@ -507,66 +503,12 @@ class ConcurrentReferenceHashMapTests {
 		copy.forEach(entry -> assertThat(entrySet.contains(entry)).isFalse());
 	}
 
-	@Test
-	@Disabled("Intended for use during development only")
-	void shouldBeFasterThanSynchronizedMap() throws InterruptedException {
-		Map<Integer, WeakReference<String>> synchronizedMap = Collections.synchronizedMap(new WeakHashMap<Integer, WeakReference<String>>());
-		StopWatch mapTime = timeMultiThreaded("SynchronizedMap", synchronizedMap, v -> new WeakReference<>(String.valueOf(v)));
-		System.out.println(mapTime.prettyPrint());
-
-		this.map.setDisableTestHooks(true);
-		StopWatch cacheTime = timeMultiThreaded("WeakConcurrentCache", this.map, String::valueOf);
-		System.out.println(cacheTime.prettyPrint());
-
-		// We should be at least 4 time faster
-		assertThat(cacheTime.getTotalTimeSeconds()).isLessThan(mapTime.getTotalTimeSeconds() / 4.0);
-	}
-
 	@Test
 	void shouldSupportNullReference() {
 		// GC could happen during restructure so we must be able to create a reference for a null entry
 		map.createReferenceManager().createReference(null, 1234, null);
 	}
 
-	/**
-	 * Time a multi-threaded access to a cache.
-	 * @return the timing stopwatch
-	 */
-	private <V> StopWatch timeMultiThreaded(String id, final Map<Integer, V> map,
-			ValueFactory<V> factory) throws InterruptedException {
-
-		StopWatch stopWatch = new StopWatch(id);
-		for (int i = 0; i < 500; i++) {
-			map.put(i, factory.newValue(i));
-		}
-		Thread[] threads = new Thread[30];
-		stopWatch.start("Running threads");
-		for (int threadIndex = 0; threadIndex < threads.length; threadIndex++) {
-			threads[threadIndex] = new Thread("Cache access thread " + threadIndex) {
-				@Override
-				public void run() {
-					for (int j = 0; j < 1000; j++) {
-						for (int i = 0; i < 1000; i++) {
-							map.get(i);
-						}
-					}
-				}
-			};
-		}
-		for (Thread thread : threads) {
-			thread.start();
-		}
-
-		for (Thread thread : threads) {
-			if (thread.isAlive()) {
-				thread.join(2000);
-			}
-		}
-		stopWatch.stop();
-		return stopWatch;
-	}
-
-
 	private interface ValueFactory<V> {
 
 		V newValue(int k);