Wait for a resume event to run the main() method after a page refresh

dwds/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 24.1.0-wip
 
 - Fix bug where debugging clients are not aware of service extensions when connecting to a new web app. - [#2388](https://github.com/dart-lang/webdev/pull/2388)
+- Respect the value of `pause_isolates_on_start` during page-refreshes. - [#2431](https://github.com/dart-lang/webdev/pull/2431)
 
 ## 24.0.0
 

dwds/lib/dart_web_debug_service.dart

@@ -139,7 +139,4 @@ class Dwds {
       debugSettings.enableDebugging,
     );
   }
-
-  bool shouldPauseIsolatesOnStart(String appId) =>
-      _devHandler.shouldPauseIsolatesOnStart(appId);
 }

dwds/lib/src/connections/app_connection.dart

@@ -18,8 +18,9 @@ class AppConnection {
   final _startedCompleter = Completer<void>();
   final _doneCompleter = Completer<void>();
   final SocketConnection _connection;
+  final Future<void> _readyToRunMain;
 
-  AppConnection(this.request, this._connection) {
+  AppConnection(this.request, this._connection, this._readyToRunMain) {
     safeUnawaited(_connection.sink.done.then((v) => _doneCompleter.complete()));
   }
 
@@ -34,6 +35,12 @@ class AppConnection {
     if (_startedCompleter.isCompleted) {
       throw StateError('Main has already started.');
     }
+
+    safeUnawaited(_runMain());
+  }
+
+  Future<void> _runMain() async {
+    await _readyToRunMain;
     _connection.sink.add(jsonEncode(serializers.serialize(RunRequest())));
     _startedCompleter.complete();
   }

dwds/lib/src/dwds_vm_client.dart

@@ -428,7 +428,7 @@ void _waitForResumeEventToRunMain(
   final issuedReadyToRunMainCompleter = Completer<void>();
 
   final resumeEventsSubscription =
-      chromeProxyService.resumeAfterHotRestartEventsStream.listen((_) async {
+      chromeProxyService.resumeAfterRestartEventsStream.listen((_) async {
     await chromeProxyService.inspector.jsEvaluate('\$dartReadyToRunMain();');
     if (!issuedReadyToRunMainCompleter.isCompleted) {
       issuedReadyToRunMainCompleter.complete();

dwds/lib/src/handlers/dev_handler.dart

@@ -121,9 +121,6 @@ class DevHandler {
         _servicesByAppId.clear();
       }();
 
-  bool shouldPauseIsolatesOnStart(String appId) =>
-      _servicesByAppId[appId]?.chromeProxyService.pauseIsolatesOnStart ?? false;
-
   void _emitBuildResults(BuildResult result) {
     if (result.status != BuildStatus.succeeded) return;
     for (var injectedConnection in _injectedConnections) {
@@ -441,7 +438,12 @@ class DevHandler {
     // were previously launched and create the new isolate.
     final services = _servicesByAppId[message.appId];
     final existingConnection = _appConnectionByAppId[message.appId];
-    final connection = AppConnection(message, sseConnection);
+    // Completer to indicate when the app's main() method is ready to be run.
+    // Its future is passed to the AppConnection so that it can be awaited on
+    // before running the app's main() method:
+    final readyToRunMainCompleter = Completer<void>();
+    final connection =
+        AppConnection(message, sseConnection, readyToRunMainCompleter.future);
 
     // We can take over a connection if there is no connectedInstanceId (this
     // means the client completely disconnected), or if the existing
@@ -460,13 +462,53 @@ class DevHandler {
 
       // Reconnect to existing service.
       services.connectedInstanceId = message.instanceId;
+
+      if (services.chromeProxyService.pauseIsolatesOnStart) {
+        // If the pause-isolates-on-start flag is set, we need to wait for
+        // the resume event to run the app's main() method.
+        _waitForResumeEventToRunMain(
+          services.chromeProxyService.resumeAfterRestartEventsStream,
+          readyToRunMainCompleter,
+        );
+      } else {
+        // Otherwise, we can run the app's main() method immediately.
+        readyToRunMainCompleter.complete();
+      }
+
       await services.chromeProxyService.createIsolate(connection);
+    } else {
+      // If this is the initial app connection, we can run the app's main()
+      // method immediately.
+      readyToRunMainCompleter.complete();
     }
     _appConnectionByAppId[message.appId] = connection;
     _connectedApps.add(connection);
     return connection;
   }
 
+  /// Waits for a resume event to trigger the app's main() method.
+  ///
+  /// The [readyToRunMainCompleter]'s future will be passed to the
+  /// [AppConnection] so that it can be awaited on before running the app's
+  /// main() method.
+  void _waitForResumeEventToRunMain(
+    Stream<String> resumeEventsStream,
+    Completer<void> readyToRunMainCompleter,
+  ) {
+    final resumeEventsSubscription = resumeEventsStream.listen((_) {
+      readyToRunMainCompleter.complete();
+      if (!readyToRunMainCompleter.isCompleted) {
+        readyToRunMainCompleter.complete();
+      }
+    });
+
+    safeUnawaited(
+      readyToRunMainCompleter.future.then((_) {
+        resumeEventsSubscription.cancel();
+      }),
+    );
+  }
+
   void _handleIsolateExit(AppConnection appConnection) {
     _servicesByAppId[appConnection.request.appId]
         ?.chromeProxyService

dwds/lib/src/services/chrome_proxy_service.dart

@@ -99,18 +99,18 @@ class ChromeProxyService implements VmServiceInterface {
   /// This value can be updated at runtime via [setFlag].
   bool get pauseIsolatesOnStart => _pauseIsolatesOnStart;
 
-  final _resumeAfterHotRestartEventsController =
+  final _resumeAfterRestartEventsController =
       StreamController<String>.broadcast();
 
   /// A global stream of resume events.
   ///
   /// The values in the stream are the isolates IDs for the resume event.
   ///
-  /// IMPORTANT: This should only be listened to during a hot-restart. The
-  /// debugger ignores any resume events as long as there is a subscriber to
-  /// this stream.
-  Stream<String> get resumeAfterHotRestartEventsStream =>
-      _resumeAfterHotRestartEventsController.stream;
+  /// IMPORTANT: This should only be listened to during a hot-restart or page
+  /// refresh. The debugger ignores any resume events as long as there is a
+  /// subscriber to this stream.
+  Stream<String> get resumeAfterRestartEventsStream =>
+      _resumeAfterRestartEventsController.stream;
 
   final _logger = Logger('ChromeProxyService');
 
@@ -1147,8 +1147,8 @@ ${globalToolConfiguration.loadStrategy.loadModuleSnippet}("dart_sdk").developer.
   }) async {
     // If there is a subscriber listening for a resume event after hot-restart,
     // then add the event to the stream and skip processing it.
-    if (_resumeAfterHotRestartEventsController.hasListener) {
-      _resumeAfterHotRestartEventsController.add(isolateId);
+    if (_resumeAfterRestartEventsController.hasListener) {
+      _resumeAfterRestartEventsController.add(isolateId);
       return Success();
     }
     if (inspector.appConnection.isStarted) {

dwds/test/chrome_proxy_service_test.dart

@@ -2070,9 +2070,8 @@ void main() {
           service.setFlag('pause_isolates_on_start', 'true'),
           completion(_isSuccess),
         );
-        final appId = context.appConnection.request.appId;
         expect(
-          context.dwds!.shouldPauseIsolatesOnStart(appId),
+          context.service.pauseIsolatesOnStart,
           equals(true),
         );
       });
@@ -2083,9 +2082,8 @@ void main() {
           service.setFlag('pause_isolates_on_start', 'false'),
           completion(_isSuccess),
         );
-        final appId = context.appConnection.request.appId;
         expect(
-          context.dwds!.shouldPauseIsolatesOnStart(appId),
+          context.service.pauseIsolatesOnStart,
           equals(false),
         );
       });

dwds/test/reload_test.dart

@@ -531,7 +531,8 @@ void main() {
       undoEdit();
     });
 
-    test('does not run app until there is a resume event', () async {
+    test('after hot-restart, does not run app until there is a resume event',
+        () async {
       await makeEditAndWaitForRebuild();
 
       final eventsDone = expectLater(
@@ -563,6 +564,36 @@ void main() {
       final sourceAfterResume = await context.webDriver.pageSource;
       expect(sourceAfterResume.contains(newString), isTrue);
     });
+
+    test('after page refresh, does not run app until there is a resume event',
+        () async {
+      await makeEditAndWaitForRebuild();
+
+      await context.webDriver.driver.refresh();
+
+      final eventsDone = expectLater(
+        client.onIsolateEvent,
+        emitsThrough(
+          emitsInOrder([
+            _hasKind(EventKind.kIsolateExit),
+            _hasKind(EventKind.kIsolateStart),
+            _hasKind(EventKind.kIsolateRunnable),
+          ]),
+        ),
+      );
+
+      await eventsDone;
+
+      final sourceBeforeResume = await context.webDriver.pageSource;
+      expect(sourceBeforeResume.contains(newString), isFalse);
+
+      final vm = await client.getVM();
+      final isolateId = vm.isolates!.first.id!;
+      await client.resume(isolateId);
+
+      final sourceAfterResume = await context.webDriver.pageSource;
+      expect(sourceAfterResume.contains(newString), isTrue);
+    });
   });
 }