Fix a race condition in vmservice_test.dart (#23835)

Fixes https://github.com/flutter/flutter/issues/19273

packages/flutter_tools/lib/src/resident_runner.dart

@@ -82,15 +82,13 @@ class FlutterDevice {
     vmServices = localVmServices;
   }
 
-  Future<void> refreshViews() {
+  Future<void> refreshViews() async {
     if (vmServices == null || vmServices.isEmpty)
       return Future<void>.value(null);
     final List<Future<void>> futures = <Future<void>>[];
     for (VMService service in vmServices)
-      futures.add(service.vm.refreshViews());
-    final Completer<void> completer = Completer<void>();
-    Future.wait(futures).whenComplete(() => completer.complete(null)); // ignore: unawaited_futures
-    return completer.future;
+      futures.add(service.vm.refreshViews(waitForViews: true));
+    await Future.wait(futures);
   }
 
   List<FlutterView> get views {
@@ -490,8 +488,10 @@ abstract class ResidentRunner {
   }
 
   Future<void> refreshViews() async {
+    final List<Future<void>> futures = <Future<void>>[];
     for (FlutterDevice device in flutterDevices)
-      await device.refreshViews();
+      futures.add(device.refreshViews());
+    await Future.wait(futures);
   }
 
   Future<void> _debugDumpApp() async {

packages/flutter_tools/lib/src/run_hot.dart

@@ -163,7 +163,10 @@ class HotRunner extends ResidentRunner {
   }) async {
     _didAttach = true;
     try {
-      await connectToServiceProtocol(reloadSources: _reloadSourcesService, compileExpression: _compileExpressionService);
+      await connectToServiceProtocol(
+        reloadSources: _reloadSourcesService,
+        compileExpression: _compileExpressionService,
+      );
     } catch (error) {
       printError('Error connecting to the service protocol: $error');
       return 2;
@@ -189,8 +192,10 @@ class HotRunner extends ResidentRunner {
     }
     final Stopwatch initialUpdateDevFSsTimer = Stopwatch()..start();
     final bool devfsResult = await _updateDevFS(fullRestart: true);
-    _addBenchmarkData('hotReloadInitialDevFSSyncMilliseconds',
-        initialUpdateDevFSsTimer.elapsed.inMilliseconds);
+    _addBenchmarkData(
+      'hotReloadInitialDevFSSyncMilliseconds',
+      initialUpdateDevFSsTimer.elapsed.inMilliseconds,
+    );
     if (!devfsResult)
       return 3;
 
@@ -276,7 +281,7 @@ class HotRunner extends ResidentRunner {
 
     return attach(
       connectionInfoCompleter: connectionInfoCompleter,
-      appStartedCompleter: appStartedCompleter
+      appStartedCompleter: appStartedCompleter,
     );
   }
 

packages/flutter_tools/lib/src/vmservice.dart

@@ -105,7 +105,7 @@ const Duration kShortRequestTimeout = Duration(seconds: 5);
 // TODO(flutter/flutter#23031): Test this.
 /// A connection to the Dart VM Service.
 class VMService {
-  VMService._(
+  VMService(
     this._peer,
     this.httpAddress,
     this.wsAddress,
@@ -236,7 +236,7 @@ class VMService {
     final Uri wsUri = httpUri.replace(scheme: 'ws', path: fs.path.join(httpUri.path, 'ws'));
     final StreamChannel<String> channel = await _openChannel(wsUri);
     final rpc.Peer peer = rpc.Peer.withoutJson(jsonDocument.bind(channel));
-    final VMService service = VMService._(peer, httpUri, wsUri, requestTimeout, reloadSources, compileExpression);
+    final VMService service = VMService(peer, httpUri, wsUri, requestTimeout, reloadSources, compileExpression);
     // This call is to ensure we are able to establish a connection instead of
     // keeping on trucking and failing farther down the process.
     await service._sendRequest('getVersion', const <String, dynamic>{});
@@ -311,7 +311,7 @@ class VMService {
     final Map<String, dynamic> eventIsolate = eventData['isolate'];
 
     // Log event information.
-    printTrace(data.toString());
+    printTrace('Notification from VM: $data');
 
     ServiceEvent event;
     if (eventIsolate != null) {
@@ -341,15 +341,9 @@ class VMService {
   }
 
   /// Reloads the VM.
-  Future<VM> getVM() async {
-    return await _vm.reload();
-  }
+  Future<void> getVM() async => await vm.reload();
 
-  Future<void> refreshViews() async {
-    if (!vm.isFlutterEngine)
-      return;
-    await vm.refreshViews();
-  }
+  Future<void> refreshViews({ bool waitForViews = false }) => vm.refreshViews(waitForViews: waitForViews);
 }
 
 /// An error that is thrown when constructing/updating a service object.
@@ -371,9 +365,8 @@ String _stripRef(String type) => _hasRef(type) ? type.substring(1) : type;
 /// to return a cached / canonicalized object.
 void _upgradeCollection(dynamic collection,
                         ServiceObjectOwner owner) {
-  if (collection is ServiceMap) {
+  if (collection is ServiceMap)
     return;
-  }
   if (collection is Map<String, dynamic>) {
     _upgradeMap(collection, owner);
   } else if (collection is List) {
@@ -382,7 +375,7 @@ void _upgradeCollection(dynamic collection,
 }
 
 void _upgradeMap(Map<String, dynamic> map, ServiceObjectOwner owner) {
-  map.forEach((String k, dynamic v) {
+  map.forEach((String k, Object v) {
     if ((v is Map<String, dynamic>) && _isServiceMap(v)) {
       map[k] = owner.getFromMap(v);
     } else if (v is List) {
@@ -394,8 +387,8 @@ void _upgradeMap(Map<String, dynamic> map, ServiceObjectOwner owner) {
 }
 
 void _upgradeList(List<dynamic> list, ServiceObjectOwner owner) {
-  for (int i = 0; i < list.length; i++) {
-    final dynamic v = list[i];
+  for (int i = 0; i < list.length; i += 1) {
+    final Object v = list[i];
     if ((v is Map<String, dynamic>) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is List) {
@@ -477,9 +470,8 @@ abstract class ServiceObject {
 
   /// If this is not already loaded, load it. Otherwise reload.
   Future<ServiceObject> load() async {
-    if (loaded) {
+    if (loaded)
       return this;
-    }
     return reload();
   }
 
@@ -499,15 +491,12 @@ abstract class ServiceObject {
     // We should always reload the VM.
     // We can't reload objects without an id.
     // We shouldn't reload an immutable and already loaded object.
-    final bool skipLoad = !isVM && (!hasId || (immutable && loaded));
-    if (skipLoad) {
+    if (!isVM && (!hasId || (immutable && loaded)))
       return this;
-    }
 
     if (_inProgressReload == null) {
       final Completer<ServiceObject> completer = Completer<ServiceObject>();
       _inProgressReload = completer.future;
-
       try {
         final Map<String, dynamic> response = await _fetchDirect();
         if (_stripRef(response['type']) == 'Sentinel') {
@@ -661,9 +650,7 @@ class VM extends ServiceObjectOwner {
   VM get vm => this;
 
   @override
-  Future<Map<String, dynamic>> _fetchDirect() async {
-    return invokeRpcRaw('getVM');
-  }
+  Future<Map<String, dynamic>> _fetchDirect() => invokeRpcRaw('getVM');
 
   @override
   void _update(Map<String, dynamic> map, bool mapIsRef) {
@@ -675,11 +662,9 @@ class VM extends ServiceObjectOwner {
     _upgradeCollection(map, this);
     _loaded = true;
 
-    // TODO(johnmccutchan): Extract any properties we care about here.
     _pid = map['pid'];
-    if (map['_heapAllocatedMemoryUsage'] != null) {
+    if (map['_heapAllocatedMemoryUsage'] != null)
       _heapAllocatedMemoryUsage = map['_heapAllocatedMemoryUsage'];
-    }
     _maxRSS = map['_maxRSS'];
     _embedder = map['_embedder'];
 
@@ -818,6 +803,13 @@ class VM extends ServiceObjectOwner {
     return Future<Isolate>.value(_isolateCache[isolateId]);
   }
 
+  static String _truncate(String message, int width, String ellipsis) {
+    assert(ellipsis.length < width);
+    if (message.length <= width)
+      return message;
+    return message.substring(0, width - ellipsis.length) + ellipsis;
+  }
+
   /// Invoke the RPC and return the raw response.
   ///
   /// If `timeoutFatal` is false, then a timeout will result in a null return
@@ -827,14 +819,14 @@ class VM extends ServiceObjectOwner {
     Duration timeout,
     bool timeoutFatal = true,
   }) async {
-    printTrace('$method: $params');
-
+    printTrace('Sending to VM service: $method($params)');
     assert(params != null);
     timeout ??= _vmService._requestTimeout;
     try {
       final Map<String, dynamic> result = await _vmService
           ._sendRequest(method, params)
           .timeout(timeout);
+      printTrace('Result: ${_truncate(result.toString(), 250, '...')}');
       return result;
     } on TimeoutException {
       printTrace('Request to Dart VM Service timed out: $method($params)');
@@ -949,12 +941,29 @@ class VM extends ServiceObjectOwner {
     return invokeRpcRaw('_getVMTimeline', timeout: kLongRequestTimeout);
   }
 
-  Future<void> refreshViews() {
+  Future<void> refreshViews({ bool waitForViews = false }) async {
+    assert(waitForViews != null);
+    assert(loaded);
     if (!isFlutterEngine)
-      return Future<void>.value();
+      return;
+    int failCount = 0;
+    while (true) {
       _viewCache.clear();
-    // Send one per-application request that refreshes all views in the app.
-    return vmService.vm.invokeRpc<ServiceObject>('_flutter.listViews', timeout: kLongRequestTimeout);
+      // When the future returned by invokeRpc() below returns,
+      // the _viewCache will have been updated.
+      // This message updates all the views of every isolate.
+      await vmService.vm.invokeRpc<ServiceObject>(
+        '_flutter.listViews',
+        timeout: kLongRequestTimeout,
+      );
+      if (_viewCache.values.isNotEmpty || !waitForViews)
+        return;
+      failCount += 1;
+      if (failCount == 5) // waited 200ms
+        printStatus('Flutter is taking longer than expected to report its views. Still trying...');
+      await Future<void>.delayed(const Duration(milliseconds: 50));
+      await reload();
+    }
   }
 
   Iterable<FlutterView> get views => _viewCache.values;
@@ -1080,9 +1089,7 @@ class Isolate extends ServiceObjectOwner {
   }
 
   @override
-  Future<Map<String, dynamic>> _fetchDirect() {
-    return invokeRpcRaw('getIsolate');
-  }
+  Future<Map<String, dynamic>> _fetchDirect() => invokeRpcRaw('getIsolate');
 
   /// Invoke the RPC and return the raw response.
   Future<Map<String, dynamic>> invokeRpcRaw(String method, {
@@ -1427,7 +1434,7 @@ class FlutterView extends ServiceObject {
                              packagesUri,
                              assetsDirectoryUri);
     await completer.future;
-    await owner.vm.refreshViews();
+    await owner.vm.refreshViews(waitForViews: true);
     await subscription.cancel();
   }
 

packages/flutter_tools/test/vmservice_test.dart

@@ -2,12 +2,158 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
+import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/vmservice.dart';
+import 'package:json_rpc_2/json_rpc_2.dart' as rpc;
+import 'package:quiver/testing/async.dart';
 
 import 'src/common.dart';
 import 'src/context.dart';
+import 'src/mocks.dart';
+
+class MockPeer implements rpc.Peer {
+  @override
+  Future<dynamic> get done async {
+    throw 'unexpected call to done';
+  }
+
+  @override
+  bool get isClosed {
+    throw 'unexpected call to isClosed';
+  }
+
+  @override
+  Future<dynamic> close() async {
+    throw 'unexpected call to close()';
+  }
+
+  @override
+  Future<dynamic> listen() async {
+    // this does get called
+  }
+
+  @override
+  void registerFallback(dynamic callback(rpc.Parameters parameters)) {
+    throw 'unexpected call to registerFallback';
+  }
+
+  @override
+  void registerMethod(String name, Function callback) {
+    // this does get called
+  }
+
+  @override
+  void sendNotification(String method, [ dynamic parameters ]) {
+    throw 'unexpected call to sendNotification';
+  }
+
+  bool isolatesEnabled = false;
+
+  Future<void> _getVMLatch;
+  Completer<void> _currentGetVMLatchCompleter;
+
+  void tripGetVMLatch() {
+    final Completer<void> lastCompleter = _currentGetVMLatchCompleter;
+    _currentGetVMLatchCompleter = Completer<void>();
+    _getVMLatch = _currentGetVMLatchCompleter.future;
+    lastCompleter?.complete();
+  }
+
+  int returnedFromSendRequest = 0;
+
+  @override
+  Future<dynamic> sendRequest(String method, [ dynamic parameters ]) async {
+    if (method == 'getVM')
+      await _getVMLatch;
+    await Future<void>.delayed(Duration.zero);
+    returnedFromSendRequest += 1;
+    if (method == 'getVM') {
+      return <String, dynamic>{
+        'type': 'VM',
+        'name': 'vm',
+        'architectureBits': 64,
+        'targetCPU': 'x64',
+        'hostCPU': '      Intel(R) Xeon(R) CPU    E5-1650 v2 @ 3.50GHz',
+        'version': '2.1.0-dev.7.1.flutter-45f9462398 (Fri Oct 19 19:27:56 2018 +0000) on "linux_x64"',
+        '_profilerMode': 'Dart',
+        '_nativeZoneMemoryUsage': 0,
+        'pid': 103707,
+        'startTime': 1540426121876,
+        '_embedder': 'Flutter',
+        '_maxRSS': 312614912,
+        '_currentRSS': 33091584,
+        'isolates': isolatesEnabled ? <dynamic>[
+          <String, dynamic>{
+            'type': '@Isolate',
+            'fixedId': true,
+            'id': 'isolates/242098474',
+            'name': 'main.dart:main()',
+            'number': 242098474,
+          },
+        ] : <dynamic>[],
+      };
+    }
+    if (method == 'getIsolate') {
+      return <String, dynamic>{
+        'type': 'Isolate',
+        'fixedId': true,
+        'id': 'isolates/242098474',
+        'name': 'main.dart:main()',
+        'number': 242098474,
+        '_originNumber': 242098474,
+        'startTime': 1540488745340,
+        '_heaps': <String, dynamic>{
+          'new': <String, dynamic>{
+            'used': 0,
+            'capacity': 0,
+            'external': 0,
+            'collections': 0,
+            'time': 0.0,
+            'avgCollectionPeriodMillis': 0.0,
+          },
+          'old': <String, dynamic>{
+            'used': 0,
+            'capacity': 0,
+            'external': 0,
+            'collections': 0,
+            'time': 0.0,
+            'avgCollectionPeriodMillis': 0.0,
+          },
+        },
+      };
+    }
+    if (method == '_flutter.listViews') {
+      return <String, dynamic>{
+        'type': 'FlutterViewList',
+        'views': isolatesEnabled ? <dynamic>[
+          <String, dynamic>{
+            'type': 'FlutterView',
+            'id': '_flutterView/0x4a4c1f8',
+            'isolate': <String, dynamic>{
+              'type': '@Isolate',
+              'fixedId': true,
+              'id': 'isolates/242098474',
+              'name': 'main.dart:main()',
+              'number': 242098474,
+            },
+          },
+        ] : <dynamic>[],
+      };
+    }
+    return null;
+  }
+
+  @override
+  dynamic withBatch(dynamic callback()) {
+    throw 'unexpected call to withBatch';
+  }
+}
 
 void main() {
+  final MockStdio mockStdio = MockStdio();
   group('VMService', () {
     testUsingContext('fails connection eagerly in the connect() method', () async {
       expect(
@@ -15,5 +161,73 @@ void main() {
         throwsToolExit(),
       );
     });
+
+    testUsingContext('refreshViews', () {
+      FakeAsync().run((FakeAsync time) {
+        bool done = false;
+        final MockPeer mockPeer = MockPeer();
+        expect(mockPeer.returnedFromSendRequest, 0);
+        final VMService vmService = VMService(mockPeer, null, null, const Duration(seconds: 1), null, null);
+        vmService.getVM().then((void value) { done = true; });
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 0);
+        time.elapse(Duration.zero);
+        expect(done, isTrue);
+        expect(mockPeer.returnedFromSendRequest, 1);
+
+        done = false;
+        mockPeer.tripGetVMLatch(); // this blocks the upcoming getVM call
+        final Future<void> ready = vmService.refreshViews(waitForViews: true);
+        ready.then((void value) { done = true; });
+        expect(mockPeer.returnedFromSendRequest, 1);
+        time.elapse(Duration.zero); // this unblocks the listViews call which returns nothing
+        expect(mockPeer.returnedFromSendRequest, 2);
+        time.elapse(const Duration(milliseconds: 50)); // the last listViews had no views, so it waits 50ms, then calls getVM
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 2);
+        mockPeer.tripGetVMLatch(); // this unblocks the getVM call
+        expect(mockPeer.returnedFromSendRequest, 2);
+        time.elapse(Duration.zero); // here getVM returns with no isolates and listViews returns no views
+        expect(mockPeer.returnedFromSendRequest, 4);
+        time.elapse(const Duration(milliseconds: 50)); // so refreshViews waits another 50ms
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 4);
+        mockPeer.tripGetVMLatch(); // this unblocks the getVM call
+        expect(mockPeer.returnedFromSendRequest, 4);
+        time.elapse(Duration.zero); // here getVM returns with no isolates and listViews returns no views
+        expect(mockPeer.returnedFromSendRequest, 6);
+        time.elapse(const Duration(milliseconds: 50)); // so refreshViews waits another 50ms
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 6);
+        mockPeer.tripGetVMLatch(); // this unblocks the getVM call
+        expect(mockPeer.returnedFromSendRequest, 6);
+        time.elapse(Duration.zero); // here getVM returns with no isolates and listViews returns no views
+        expect(mockPeer.returnedFromSendRequest, 8);
+        time.elapse(const Duration(milliseconds: 50)); // so refreshViews waits another 50ms
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 8);
+        mockPeer.tripGetVMLatch(); // this unblocks the getVM call
+        expect(mockPeer.returnedFromSendRequest, 8);
+        time.elapse(Duration.zero); // here getVM returns with no isolates and listViews returns no views
+        expect(mockPeer.returnedFromSendRequest, 10);
+        const String message = 'Flutter is taking longer than expected to report its views. Still trying...\n';
+        expect(mockStdio.writtenToStdout.join(''), message);
+        expect(mockStdio.writtenToStderr.join(''), '');
+        time.elapse(const Duration(milliseconds: 50)); // so refreshViews waits another 50ms
+        expect(done, isFalse);
+        expect(mockPeer.returnedFromSendRequest, 10);
+        mockPeer.isolatesEnabled = true;
+        mockPeer.tripGetVMLatch(); // this unblocks the getVM call
+        expect(mockPeer.returnedFromSendRequest, 10);
+        time.elapse(Duration.zero); // now it returns an isolate and the listViews call returns views
+        expect(mockPeer.returnedFromSendRequest, 13);
+        expect(done, isTrue);
+        expect(mockStdio.writtenToStdout.join(''), message);
+        expect(mockStdio.writtenToStderr.join(''), '');
+      });
+    }, overrides: <Type, Generator>{
+      Logger: () => StdoutLogger(),
+      Stdio: () => mockStdio,
+    });
   });
 }