Fix DTD freezes when opening projects, and EDT freezes when the theme changed and opening embedded DevTools (flutter#8479)

*(originally with
flutter#8477

Summary
- Fix frequent “Timed out waiting for DTD websocket to start” errors
when opening projects.
- Fix EDT freezes caused by:
- Synchronous JxBrowser Engine initialization when opening embedded
DevTools.
- Blocking ExecutorService lifecycle on theme change (JDK 21
ExecutorService.close() awaits termination).

Changes
- DtdUtils
- Refactor readyDtdService to be truly asynchronous using a shared
ScheduledExecutorService for periodic polling (no blocking).
- De-duplicate and cache the in-flight Future per Project to avoid
redundant polling under concurrency.
- Preserve an overall timeout (~20s by default). On timeout or error,
complete exceptionally and clear the cache to allow subsequent retries.
- EmbeddedJxBrowser.openEmbeddedTab:
- Avoid initializing JxBrowser Engine on the EDT; show “installation in
progress” UI until async init completes.
- This removes the fallback compareAndSet(null, getEngine()) path that
could call Engine.newInstance(...) on EDT and freeze it.
- FlutterInitializer.sendThemeChangedEvent:
- Send themeChanged asynchronously: remove .get() blocking; use a shared
scheduler with debounce.
- If DTD becomes ready later, the event is sent then; if it times out,
gracefully skip with debug-level logging (no startup errors).
- Use shared AppScheduledExecutor (AppExecutorUtil) instead of
creating/closing a new executor per event.
- Remove try-with-resources that triggers ExecutorService.close() on EDT
with JDK 21.

Notes
- Added comments explaining why Engine initialization must not occur on
EDT and how JDK 21 changed ExecutorService.close().

Fixes
- Fixes flutter#7794
- Fixes flutter#8394
- Fixes flutter#8478

Testing
- Manual:
  - Open Flutter projects; no error logs about DTD timeout.
  - Switch IDE themes repeatedly; no UI freeze.
- Open DevTools (embedded) after clean startup and after JxBrowser
installation completes; no EDT freeze, proper “installing...” UX during
setup.

Author: AlexV525

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Made dev release daily instead of weekly
 - Set the device selector component to opaque during its creation to avoid an unexpected background color (#8471)
 - Refactored `DeviceSelectorAction` and add rich icons to different platform devices (#8475)
+- Fix DTD freezes when opening projects, and EDT freezes when the theme is changed and opening embedded DevTools (#8477)
 
 ## 87.1.0
 

src/io/flutter/FlutterInitializer.java

@@ -29,7 +29,6 @@
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.util.concurrency.AppExecutorUtil;
 import com.intellij.util.messages.MessageBusConnection;
-import com.jetbrains.lang.dart.ide.toolingDaemon.DartToolingDaemonService;
 import de.roderick.weberknecht.WebSocketException;
 import io.flutter.android.IntelliJAndroidSdk;
 import io.flutter.bazel.WorkspaceCache;
@@ -59,8 +58,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 
@@ -78,6 +76,10 @@ public class FlutterInitializer extends FlutterProjectActivity {
 
   private @NotNull AtomicLong lastScheduledThemeChangeTime = new AtomicLong();
 
+  // Shared scheduler to avoid creating/closing executors on EDT
+  @NotNull
+  private final ScheduledExecutorService scheduler = AppExecutorUtil.getAppScheduledExecutorService();
+
   @Override
   public void executeProjectStartup(@NotNull Project project) {
     log().info("Executing Flutter plugin startup for project: " + project.getName());
@@ -253,57 +255,59 @@ private void sendThemeChangedEvent(@NotNull Project project) {
     lastScheduledThemeChangeTime.set(requestTime);
 
     // Schedule event to be sent in a second if nothing more recent has come in.
-    try (var executor = Executors.newSingleThreadScheduledExecutor()) {
-      executor.schedule(() -> {
-        if (lastScheduledThemeChangeTime.get() != requestTime) {
-          // A more recent request has been set, so drop this request.
-          return;
-        }
+    scheduler.schedule(() -> {
+      if (lastScheduledThemeChangeTime.get() != requestTime) {
+        // A more recent request has been set, so drop this request.
+        return;
+      }
 
-        final JsonObject params = new JsonObject();
-        params.addProperty("eventKind", "themeChanged");
-        params.addProperty("streamId", "Editor");
+      final JsonObject params = new JsonObject();
+      params.addProperty("eventKind", "themeChanged");
+      params.addProperty("streamId", "Editor");
 
-        final JsonObject themeData = new JsonObject();
-        final DevToolsUtils utils = new DevToolsUtils();
-        themeData.addProperty("isDarkMode", Boolean.FALSE.equals(utils.getIsBackgroundBright()));
-        themeData.addProperty("backgroundColor", utils.getColorHexCode());
-        themeData.addProperty("fontSize", utils.getFontSize().intValue());
+      final JsonObject themeData = new JsonObject();
+      final DevToolsUtils utils = new DevToolsUtils();
+      themeData.addProperty("isDarkMode", Boolean.FALSE.equals(utils.getIsBackgroundBright()));
+      themeData.addProperty("backgroundColor", utils.getColorHexCode());
+      themeData.addProperty("fontSize", utils.getFontSize().intValue());
 
-        final JsonObject eventData = new JsonObject();
-        eventData.add("theme", themeData);
-        params.add("eventData", eventData);
+      final JsonObject eventData = new JsonObject();
+      eventData.add("theme", themeData);
+      params.add("eventData", eventData);
 
-        try {
-          final DtdUtils dtdUtils = new DtdUtils();
-          final DartToolingDaemonService dtdService = dtdUtils.readyDtdService(project).get();
+      final DtdUtils dtdUtils = new DtdUtils();
+      dtdUtils.readyDtdService(project)
+        .thenAccept(dtdService -> {
           if (dtdService == null) {
-            log().error("Unable to send theme changed event because DTD service is null");
+            log().warn("Unable to send theme changed event because DTD service is null");
             return;
           }
-
-          dtdService.sendRequest("postEvent", params, false, object -> {
-                                   JsonObject result = object.getAsJsonObject("result");
-                                   if (result == null) {
-                                     log().error("Theme changed event returned null result");
-                                     return;
-                                   }
-                                   JsonPrimitive type = result.getAsJsonPrimitive("type");
-                                   if (type == null) {
-                                     log().error("Theme changed event result type is null");
-                                     return;
-                                   }
-                                   if (!"Success".equals(type.getAsString())) {
-                                     log().error("Theme changed event result: " + type.getAsString());
-                                   }
-                                 }
-          );
-        }
-        catch (WebSocketException | InterruptedException | ExecutionException e) {
-          log().error("Unable to send theme changed event", e);
-        }
-      }, 1, TimeUnit.SECONDS);
-    }
+          try {
+            dtdService.sendRequest("postEvent", params, false, object -> {
+              JsonObject result = object.getAsJsonObject("result");
+              if (result == null) {
+                log().error("Theme changed event returned null result");
+                return;
+              }
+              JsonPrimitive type = result.getAsJsonPrimitive("type");
+              if (type == null) {
+                log().error("Theme changed event result type is null");
+                return;
+              }
+              if (!"Success".equals(type.getAsString())) {
+                log().error("Theme changed event result: " + type.getAsString());
+              }
+            });
+          }
+          catch (WebSocketException e) {
+            log().error("Unable to send theme changed event", e);
+          }
+        })
+        .exceptionally(e -> {
+          log().debug("DTD not ready; skipping themeChanged event", e);
+          return null;
+        });
+    }, 1, TimeUnit.SECONDS);
   }
 
   private void checkSdkVersionNotification(@NotNull Project project) {

src/io/flutter/dart/DtdUtils.java

@@ -6,34 +6,48 @@
 package io.flutter.dart;
 
 import com.intellij.openapi.project.Project;
+import com.intellij.util.concurrency.AppExecutorUtil;
 import com.jetbrains.lang.dart.ide.toolingDaemon.DartToolingDaemonService;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.concurrent.CompletableFuture;
+import java.util.Map;
+import java.util.concurrent.*;
 
 public class DtdUtils {
+  private static final Map<Project, CompletableFuture<DartToolingDaemonService>> WAITERS = new ConcurrentHashMap<>();
+
   public @NotNull CompletableFuture<DartToolingDaemonService> readyDtdService(@NotNull Project project) {
-    final DartToolingDaemonService dtdService = DartToolingDaemonService.getInstance(project);
-    CompletableFuture<DartToolingDaemonService> readyService = new CompletableFuture<>();
-    int attemptsRemaining = 10;
-    final int TIME_IN_BETWEEN = 2;
-    while (attemptsRemaining > 0) {
-      attemptsRemaining--;
+    return WAITERS.computeIfAbsent(project, p -> {
+      final DartToolingDaemonService dtdService = DartToolingDaemonService.getInstance(project);
+      CompletableFuture<DartToolingDaemonService> readyService = new CompletableFuture<>();
+
       if (dtdService.getWebSocketReady()) {
         readyService.complete(dtdService);
-        break;
-      }
-      try {
-        Thread.sleep(TIME_IN_BETWEEN * 1000);
+        return readyService;
       }
-      catch (InterruptedException e) {
-        readyService.completeExceptionally(e);
-        break;
-      }
-    }
-    if (!readyService.isDone()) {
-      readyService.completeExceptionally(new Exception("Timed out waiting for DTD websocket to start"));
-    }
-    return readyService;
+
+      final ScheduledExecutorService scheduler = AppExecutorUtil.getAppScheduledExecutorService();
+
+      final ScheduledFuture<?> poll = scheduler.scheduleWithFixedDelay(() -> {
+        if (readyService.isDone()) return;
+        if (dtdService.getWebSocketReady()) {
+          readyService.complete(dtdService);
+        }
+      }, 0, 500, TimeUnit.MILLISECONDS);
+
+      final ScheduledFuture<?> timeout = scheduler.schedule(() -> {
+        readyService.completeExceptionally(new Exception("Timed out waiting for DTD websocket to start"));
+      }, 20, TimeUnit.SECONDS);
+
+      readyService.whenComplete((s, t) -> {
+        poll.cancel(false);
+        timeout.cancel(false);
+        if (t != null) {
+          WAITERS.remove(p);
+        }
+      });
+
+      return readyService;
+    });
   }
 }

src/io/flutter/jxbrowser/EmbeddedJxBrowser.java

@@ -129,6 +129,8 @@ public class EmbeddedJxBrowser extends EmbeddedBrowser {
     "Waiting for JxBrowser installation timed out. Restart your IDE to try again.";
   private static final String INSTALLATION_WAIT_FAILED = "The JxBrowser installation failed unexpectedly. Restart your IDE to try again.";
   private static final int INSTALLATION_WAIT_LIMIT_SECONDS = 30;
+
+  @NotNull
   private final AtomicReference<Engine> engineRef = new AtomicReference<>(null);
 
   private final Project project;
@@ -173,19 +175,22 @@ private EmbeddedJxBrowser(@NotNull Project project) {
   }
 
   @Override
-  public @Nullable EmbeddedTab openEmbeddedTab(ContentManager contentManager) {
+  public @Nullable EmbeddedTab openEmbeddedTab(@NotNull ContentManager contentManager) {
     manageJxBrowserDownload(contentManager);
-    if (engineRef.get() == null) {
-      engineRef.compareAndSet(null, EmbeddedBrowserEngine.getInstance().getEngine());
-    }
+    // Do NOT initialize the JxBrowser Engine on the EDT.
+    // Historically, we tried to 'fallback' and construct the Engine here when it's null:
+    //   engineRef.compareAndSet(null, EmbeddedBrowserEngine.getInstance().getEngine());
+    // That path synchronously triggers Engine.newInstance(...) which blocks (CountDownLatch.await)
+    // and can freeze the Event Dispatch Thread (see #8394).
+    //
+    // Proceed only when the engine has been initialized by the async installation callback.
     final Engine engine = engineRef.get();
     if (engine == null) {
-      showMessageWithUrlLink(jxBrowserErrorMessage(), contentManager);
+      // Show an "installation in progress" UX instead of attempting synchronous engine creation.
+      handleJxBrowserInstallationInProgress(contentManager);
       return null;
     }
-    else {
-      return new EmbeddedJxBrowserTab(engine);
-    }
+    return new EmbeddedJxBrowserTab(engine);
   }
 
   private @NotNull String jxBrowserErrorMessage() {

testSrc/unit/io/flutter/FlutterInitializerTest.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2016 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+package io.flutter;
+
+import org.junit.Test;
+
+import java.lang.reflect.Field;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.atomic.AtomicLong;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Tests for {@link FlutterInitializer}.
+ */
+public class FlutterInitializerTest {
+
+  @Test
+  public void testInitializerCanBeCreated() {
+    // Test that we can create FlutterInitializer without issues
+    // This validates that the shared scheduler field is properly initialized
+    FlutterInitializer initializer = new FlutterInitializer();
+    assertNotNull("FlutterInitializer should be created successfully", initializer);
+  }
+
+  @Test
+  public void testSchedulerFieldExists() throws Exception {
+    // Test that the scheduler field exists and is properly initialized
+    FlutterInitializer initializer = new FlutterInitializer();
+    
+    Field schedulerField = FlutterInitializer.class.getDeclaredField("scheduler");
+    schedulerField.setAccessible(true);
+    
+    Object scheduler = schedulerField.get(initializer);
+    assertNotNull("Scheduler field should be initialized", scheduler);
+    assertTrue("Scheduler should be a ScheduledExecutorService", 
+               scheduler instanceof ScheduledExecutorService);
+  }
+
+  @Test 
+  public void testDebounceFieldExists() throws Exception {
+    // Test that the debounce field exists and is properly initialized
+    FlutterInitializer initializer = new FlutterInitializer();
+    
+    Field debounceField = FlutterInitializer.class.getDeclaredField("lastScheduledThemeChangeTime");
+    debounceField.setAccessible(true);
+    
+    Object debounceTimer = debounceField.get(initializer);
+    assertNotNull("Debounce timer field should be initialized", debounceTimer);
+    assertTrue("Debounce timer should be an AtomicLong", 
+               debounceTimer instanceof AtomicLong);
+  }
+}