refactor: remove virtual thread support

Java 19 is out of support, but Gradle current does not run on Java 20:
https://github.com/gradle/gradle/issues/23488

To avoid the complexity of running the build tool on a different JDK than the
application, we temporarily remove code that depends on experimental Java 19 or
Java 20 features.

Revert once the build can run on Java 20.

6 files changed, 12 insertions, 89 deletions

diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/ProblemWebModule.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/ProblemWebModule.java
index 12e39e55..b0197c01 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/ProblemWebModule.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/ProblemWebModule.java
@@ -9,13 +9,11 @@
  */
 package tools.refinery.language.web;
 
-import org.eclipse.xtext.ide.ExecutorServiceProvider;
 import org.eclipse.xtext.web.server.XtextServiceDispatcher;
 import org.eclipse.xtext.web.server.model.IWebDocumentProvider;
 import org.eclipse.xtext.web.server.model.XtextWebDocumentAccess;
 import org.eclipse.xtext.web.server.occurrences.OccurrencesService;
 import tools.refinery.language.web.occurrences.ProblemOccurrencesService;
-import tools.refinery.language.web.xtext.VirtualThreadExecutorServiceProvider;
 import tools.refinery.language.web.xtext.server.push.PushServiceDispatcher;
 import tools.refinery.language.web.xtext.server.push.PushWebDocumentAccess;
 import tools.refinery.language.web.xtext.server.push.PushWebDocumentProvider;
@@ -39,8 +37,4 @@ public class ProblemWebModule extends AbstractProblemWebModule {
         public Class<? extends OccurrencesService> bindOccurrencesService() {
                 return ProblemOccurrencesService.class;
         }
-
-        public Class<? extends ExecutorServiceProvider> bindExecutorServiceProvider() {
-                return VirtualThreadExecutorServiceProvider.class;
-        }
 }
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
index 1924f661..ad19e77d 100644
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
+++ b/subprojects/language-web/src/main/java/tools/refinery/language/web/ServerLauncher.java
@@ -19,6 +19,7 @@ import org.eclipse.jetty.ee10.websocket.server.config.JettyWebSocketServletConta
 import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.util.resource.Resource;
 import org.eclipse.jetty.util.resource.ResourceFactory;
+import org.eclipse.jetty.util.thread.QueuedThreadPool;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import tools.refinery.language.web.config.BackendConfigServlet;
@@ -49,7 +50,8 @@ public class ServerLauncher {
         private final Server server;
 
         public ServerLauncher(InetSocketAddress bindAddress, String[] allowedOrigins, String webSocketUrl) {
-                server = VirtualThreadUtils.newServerWithVirtualThreadsThreadPool("jetty", bindAddress);
+                server = new Server(bindAddress);
+                ((QueuedThreadPool) server.getThreadPool()).setName("jetty");
                 var handler = new ServletContextHandler();
                 addSessionHandler(handler);
                 addProblemServlet(handler, allowedOrigins);
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/VirtualThreadUtils.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/VirtualThreadUtils.java
deleted file mode 100644
index 27802e0c..00000000
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/VirtualThreadUtils.java
+++ /dev/null
@@ -1,57 +0,0 @@
-/*
- * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
- *
- * SPDX-License-Identifier: EPL-2.0
- */
-package tools.refinery.language.web;
-
-import org.eclipse.jetty.server.Server;
-import org.eclipse.jetty.server.ServerConnector;
-import org.eclipse.jetty.util.thread.QueuedThreadPool;
-import org.eclipse.jetty.util.thread.ThreadPool;
-
-import java.net.InetSocketAddress;
-import java.time.Duration;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
-
-public final class VirtualThreadUtils {
-        private VirtualThreadUtils() {
-                throw new IllegalStateException("This is a static utility class and should not be instantiated directly");
-        }
-
-        public static ExecutorService newNamedVirtualThreadsExecutor(String name) {
-                // Based on
-                // https://github.com/eclipse/jetty.project/blob/83154b4ffe4767ef44981598d6c26e6a5d32e57c/jetty-server/src/main/config/etc/jetty-threadpool-virtual-preview.xml
-                return Executors.newThreadPerTaskExecutor(Thread.ofVirtual()
-                                .allowSetThreadLocals(true)
-                                .inheritInheritableThreadLocals(false)
-                                .name(name + "-virtual-", 0)
-                                .factory());
-        }
-
-        public static ThreadPool newThreadPoolWithVirtualThreadsExecutor(String name) {
-                // Based on
-                // https://github.com/eclipse/jetty.project/blob/83154b4ffe4767ef44981598d6c26e6a5d32e57c/jetty-server/src/main/config/etc/jetty-threadpool-virtual-preview.xml
-                int timeout = (int) Duration.ofMinutes(1).toMillis();
-                var threadPool = new QueuedThreadPool(200, 10, timeout, -1, null, null);
-                threadPool.setName(name);
-                threadPool.setDetailedDump(false);
-                threadPool.setVirtualThreadsExecutor(newNamedVirtualThreadsExecutor(name));
-                return threadPool;
-        }
-
-        public static Server newServerWithVirtualThreadsThreadPool(String name, InetSocketAddress listenAddress) {
-                var server = new Server(newThreadPoolWithVirtualThreadsExecutor(name));
-                var connector = new ServerConnector(server);
-                try {
-                        connector.setHost(listenAddress.getHostName());
-                        connector.setPort(listenAddress.getPort());
-                        server.addConnector(connector);
-                } catch (Exception e) {
-                        connector.close();
-                        throw e;
-                }
-                return server;
-        }
-}
diff --git a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/VirtualThreadExecutorServiceProvider.java b/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/VirtualThreadExecutorServiceProvider.java
deleted file mode 100644
index 699a09ab..00000000
--- a/subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/VirtualThreadExecutorServiceProvider.java
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
- *
- * SPDX-License-Identifier: EPL-2.0
- */
-package tools.refinery.language.web.xtext;
-
-import org.eclipse.xtext.ide.ExecutorServiceProvider;
-import tools.refinery.language.web.VirtualThreadUtils;
-
-import java.util.concurrent.ExecutorService;
-
-public class VirtualThreadExecutorServiceProvider extends ExecutorServiceProvider {
-        private static final String THREAD_POOL_NAME = "xtextWeb";
-
-        @Override
-        protected ExecutorService createInstance(String key) {
-                var name = key == null ? THREAD_POOL_NAME : THREAD_POOL_NAME + "-" + key;
-                return VirtualThreadUtils.newNamedVirtualThreadsExecutor(name);
-        }
-}
diff --git a/subprojects/language-web/src/test/java/tools/refinery/language/web/ProblemWebSocketServletIntegrationTest.java b/subprojects/language-web/src/test/java/tools/refinery/language/web/ProblemWebSocketServletIntegrationTest.java
index 53a757eb..40f5281d 100644
--- a/subprojects/language-web/src/test/java/tools/refinery/language/web/ProblemWebSocketServletIntegrationTest.java
+++ b/subprojects/language-web/src/test/java/tools/refinery/language/web/ProblemWebSocketServletIntegrationTest.java
@@ -17,9 +17,13 @@ import org.eclipse.jetty.ee10.websocket.server.config.JettyWebSocketServletConta
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpStatus;
 import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.util.thread.QueuedThreadPool;
 import org.eclipse.xtext.testing.GlobalRegistries;
 import org.eclipse.xtext.testing.GlobalRegistries.GlobalStateMemento;
-import org.junit.jupiter.api.*;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInfo;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import tools.refinery.language.web.tests.WebSocketIntegrationTestClient;
@@ -193,7 +197,8 @@ class ProblemWebSocketServletIntegrationTest {
         private void startServer(String allowedOrigins) {
                 var testName = getClass().getSimpleName() + "-" + testInfo.getDisplayName();
                 var listenAddress = new InetSocketAddress(HOSTNAME, serverPort);
-                server = VirtualThreadUtils.newServerWithVirtualThreadsThreadPool(testName, listenAddress);
+                server = new Server(listenAddress);
+                ((QueuedThreadPool) server.getThreadPool()).setName(testName);
                 var handler = new ServletContextHandler();
                 var holder = new ServletHolder(ProblemWebSocketServlet.class);
                 if (allowedOrigins != null) {
diff --git a/subprojects/language-web/src/test/java/tools/refinery/language/web/tests/AwaitTerminationExecutorServiceProvider.java b/subprojects/language-web/src/test/java/tools/refinery/language/web/tests/AwaitTerminationExecutorServiceProvider.java
index 630549d4..52acee6d 100644
--- a/subprojects/language-web/src/test/java/tools/refinery/language/web/tests/AwaitTerminationExecutorServiceProvider.java
+++ b/subprojects/language-web/src/test/java/tools/refinery/language/web/tests/AwaitTerminationExecutorServiceProvider.java
@@ -6,14 +6,14 @@
 package tools.refinery.language.web.tests;
 
 import com.google.inject.Singleton;
-import tools.refinery.language.web.xtext.VirtualThreadExecutorServiceProvider;
+import org.eclipse.xtext.ide.ExecutorServiceProvider;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ExecutorService;
 
 @Singleton
-public class AwaitTerminationExecutorServiceProvider extends VirtualThreadExecutorServiceProvider {
+public class AwaitTerminationExecutorServiceProvider extends ExecutorServiceProvider {
         private final List<RestartableCachedThreadPool> servicesToShutDown = new ArrayList<>();
 
         @Override