Refactorings for additional JMH tests

compliance/repository/src/test/java/org/eclipse/rdf4j/repository/sparql/federation/RepositoryFederatedServiceIntegrationTest.java

@@ -295,7 +295,7 @@ public void test9_connectionHandling() throws Exception {
 						.map(value -> vf.createStatement(iri("s1"), RDFS.LABEL, value))
 						.collect(Collectors.toList()));
 
-		ExecutorService executor = Executors.newFixedThreadPool(5);
+		ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
 		try {
 			for (int i = 0; i < 5; i++) {
 				executor.submit(() -> {

core/queryalgebra/evaluation/src/test/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/MinimalContextNowTest.java

@@ -49,7 +49,7 @@ public void testConcurrentAccessToNow() throws ExecutionException, InterruptedEx
 		int numberOfIterations = 100;
 		int numberOfThreads = 10;
 
-		ExecutorService executorService = Executors.newCachedThreadPool();
+		ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
 		try {
 
 			for (int i = 0; i < numberOfIterations; i++) {

core/sail/api/src/test/java/org/eclipse/rdf4j/sail/helpers/AbstractSailTest.java

@@ -101,7 +101,7 @@ public void testConcurrentAutoInit() throws Exception {
 		CountDownLatch latch = new CountDownLatch(count);
 
 		for (int i = 0; i < count; i++) {
-			new Thread(new SailGetConnectionTask(subject, latch)).start();
+			Thread.ofVirtual().start(new SailGetConnectionTask(subject, latch));
 		}
 
 		if (!latch.await(30, TimeUnit.SECONDS)) {

core/sail/lucene/src/test/java/org/eclipse/rdf4j/sail/lucene/impl/AbstractGenericLuceneTest.java

@@ -773,7 +773,7 @@ public void testMultithreadedAdd() throws InterruptedException {
 		final CountDownLatch endLatch = new CountDownLatch(numThreads);
 		final Set<Throwable> exceptions = ConcurrentHashMap.newKeySet();
 		for (int i = 0; i < numThreads; i++) {
-			new Thread(new Runnable() {
+			Thread.ofVirtual().start(new Runnable() {
 
 				private final long iterationCount = 10 + Math.round(random.nextDouble() * 100);
 
@@ -791,7 +791,7 @@ public void run() {
 						endLatch.countDown();
 					}
 				}
-			}).start();
+			});
 		}
 		startLatch.countDown();
 		endLatch.await();

core/sail/memory/src/test/java/org/eclipse/rdf4j/sail/memory/model/MemStatementListTestIT.java

@@ -106,7 +106,7 @@ public void addMultipleThreads() throws ExecutionException, InterruptedException
 
 		MemStatementList memStatementList = new MemStatementList();
 
-		ExecutorService executorService = Executors.newCachedThreadPool();
+		ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
 		try {
 
 			List<? extends Future<?>> collect = partition
@@ -153,7 +153,7 @@ public void addMultipleThreadsAndCleanupThread() throws ExecutionException, Inte
 
 		CountDownLatch countDownLatch = new CountDownLatch(1);
 
-		ExecutorService executorService = Executors.newCachedThreadPool();
+		ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
 		try {
 
 			Future<?> cleanupFuture = executorService.submit(() -> {

core/sail/shacl/src/test/java/org/eclipse/rdf4j/sail/shacl/MultithreadedTest.java

@@ -223,7 +223,7 @@ private void parallelTest(List<List<Transaction>> list, IsolationLevels isolatio
 
 		Random r = new Random(52465534);
 
-		ExecutorService executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * 2);
+		ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();
 
 		try {
 			for (int i = 0; i < 3; i++) {
@@ -467,7 +467,7 @@ private void runValidationFailuresTest(Sail sail, IsolationLevels isolationLevel
 			deadlockDetectionThread.setDaemon(true);
 			deadlockDetectionThread.start();
 
-			executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * 2);
+			executorService = Executors.newVirtualThreadPerTaskExecutor();
 
 			Utils.loadShapeData(repository, "complexBenchmark/shacl.trig");