tracing.dart 7.69 KB
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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
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import 'package:vm_service/vm_service.dart' as vm_service;
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import 'base/common.dart';
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import 'base/error_handling_io.dart';
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import 'base/file_system.dart';
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import 'base/logger.dart';
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import 'base/utils.dart';
import 'vmservice.dart';

// Names of some of the Timeline events we care about.
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const String kFlutterEngineMainEnterEventName = 'FlutterEngineMainEnter';
const String kFrameworkInitEventName = 'Framework initialization';
const String kFirstFrameBuiltEventName = 'Widgets built first useful frame';
const String kFirstFrameRasterizedEventName = 'Rasterized first useful frame';
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class Tracing {
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  Tracing({
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    required this.vmService,
    required Logger logger,
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  }) : _logger = logger;
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  static const String firstUsefulFrameEventName = kFirstFrameRasterizedEventName;
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  final FlutterVmService vmService;
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  final Logger _logger;
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  Future<void> startTracing() async {
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    await vmService.setTimelineFlags(<String>['Compiler', 'Dart', 'Embedder', 'GC']);
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    await vmService.service.clearVMTimeline();
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  }

  /// Stops tracing; optionally wait for first frame.
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  Future<Map<String, Object?>> stopTracingAndDownloadTimeline({
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    bool awaitFirstFrame = false,
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  }) async {
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    if (awaitFirstFrame) {
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      final Status status = _logger.startProgress(
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        'Waiting for application to render first frame...',
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      );
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      try {
        final Completer<void> whenFirstFrameRendered = Completer<void>();
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        try {
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          await vmService.service.streamListen(vm_service.EventStreams.kExtension);
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        } on vm_service.RPCError {
          // It is safe to ignore this error because we expect an error to be
          // thrown if we're already subscribed.
        }
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        final StringBuffer bufferedEvents = StringBuffer();
        void Function(String) handleBufferedEvent = bufferedEvents.writeln;
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        vmService.service.onExtensionEvent.listen((vm_service.Event event) {
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          handleBufferedEvent('${event.extensionKind}: ${event.extensionData}');
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          if (event.extensionKind == 'Flutter.FirstFrame') {
            whenFirstFrameRendered.complete();
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          }
        });
        bool done = false;
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        final List<FlutterView> views = await vmService.getFlutterViews();
        for (final FlutterView view in views) {
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          final String? uiIsolateId = view.uiIsolate?.id;
          if (uiIsolateId != null && await vmService
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              .flutterAlreadyPaintedFirstUsefulFrame(
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                isolateId: uiIsolateId,
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              )) {
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            done = true;
            break;
          }
        }
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        if (!done) {
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          final Timer timer = Timer(const Duration(seconds: 10), () {
            _logger.printStatus('First frame is taking longer than expected...');
            _logger.printTrace('Views:');
            for (final FlutterView view in views) {
              _logger.printTrace('id: ${view.id} isolate: ${view.uiIsolate?.id}');
            }
            _logger.printTrace('Received VM events:');
            _logger.printTrace(bufferedEvents.toString());
            // Swap to just printing new events instead of buffering.
            handleBufferedEvent = _logger.printTrace;
          });
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          await whenFirstFrameRendered.future;
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          timer.cancel();
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        }
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      // The exception is rethrown, so don't catch only Exceptions.
      } catch (exception) { // ignore: avoid_catches_without_on_clauses
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        status.cancel();
        rethrow;
      }
      status.stop();
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    }
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    final vm_service.Response? timeline = await vmService.getTimeline();
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    await vmService.setTimelineFlags(<String>[]);
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    final Map<String, Object?>? timelineJson = timeline?.json;
    if (timelineJson == null) {
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      throwToolExit(
        'The device disconnected before the timeline could be retrieved.',
      );
    }
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    return timelineJson;
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  }
}

/// Download the startup trace information from the given observatory client and
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/// store it to `$output/start_up_info.json`.
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Future<void> downloadStartupTrace(FlutterVmService vmService, {
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  bool awaitFirstFrame = true,
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  required Logger logger,
  required Directory output,
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}) async {
  final File traceInfoFile = output.childFile('start_up_info.json');
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  // Delete old startup data, if any.
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  ErrorHandlingFileSystem.deleteIfExists(traceInfoFile);
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  // Create "build" directory, if missing.
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  if (!traceInfoFile.parent.existsSync()) {
    traceInfoFile.parent.createSync();
  }
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  final Tracing tracing = Tracing(vmService: vmService, logger: logger);
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  final Map<String, Object?> timeline = await tracing.stopTracingAndDownloadTimeline(
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    awaitFirstFrame: awaitFirstFrame,
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  );

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  final File traceTimelineFile = output.childFile('start_up_timeline.json');
  traceTimelineFile.writeAsStringSync(toPrettyJson(timeline));

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  int? extractInstantEventTimestamp(String eventName) {
    final List<Object?>? traceEvents = timeline['traceEvents'] as List<Object?>?;
    if (traceEvents == null) {
      return null;
    }
    final List<Map<String, Object?>> events = List<Map<String, Object?>>.from(traceEvents);
    Map<String, Object?>? matchedEvent;
    for (final Map<String, Object?> event in events) {
      if (event['name'] == eventName) {
        matchedEvent = event;
      }
    }
    return matchedEvent == null ? null : (matchedEvent['ts'] as int?);
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  }

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  String message = 'No useful metrics were gathered.';

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  final int? engineEnterTimestampMicros = extractInstantEventTimestamp(kFlutterEngineMainEnterEventName);
  final int? frameworkInitTimestampMicros = extractInstantEventTimestamp(kFrameworkInitEventName);
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  if (engineEnterTimestampMicros == null) {
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    logger.printTrace('Engine start event is missing in the timeline: $timeline');
    throwToolExit('Engine start event is missing in the timeline. Cannot compute startup time.');
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  }

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  final Map<String, Object?> traceInfo = <String, Object?>{
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    'engineEnterTimestampMicros': engineEnterTimestampMicros,
  };

  if (frameworkInitTimestampMicros != null) {
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    final int timeToFrameworkInitMicros = frameworkInitTimestampMicros - engineEnterTimestampMicros;
    traceInfo['timeToFrameworkInitMicros'] = timeToFrameworkInitMicros;
    message = 'Time to framework init: ${timeToFrameworkInitMicros ~/ 1000}ms.';
  }

  if (awaitFirstFrame) {
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    final int? firstFrameBuiltTimestampMicros = extractInstantEventTimestamp(kFirstFrameBuiltEventName);
    final int? firstFrameRasterizedTimestampMicros = extractInstantEventTimestamp(kFirstFrameRasterizedEventName);
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    if (firstFrameBuiltTimestampMicros == null || firstFrameRasterizedTimestampMicros == null) {
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      logger.printTrace('First frame events are missing in the timeline: $timeline');
      throwToolExit('First frame events are missing in the timeline. Cannot compute startup time.');
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    }
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    // To keep our old benchmarks valid, we'll preserve the
    // timeToFirstFrameMicros as the firstFrameBuiltTimestampMicros.
    // Additionally, we add timeToFirstFrameRasterizedMicros for a more accurate
    // benchmark.
    traceInfo['timeToFirstFrameRasterizedMicros'] = firstFrameRasterizedTimestampMicros - engineEnterTimestampMicros;
    final int timeToFirstFrameMicros = firstFrameBuiltTimestampMicros - engineEnterTimestampMicros;
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    traceInfo['timeToFirstFrameMicros'] = timeToFirstFrameMicros;
    message = 'Time to first frame: ${timeToFirstFrameMicros ~/ 1000}ms.';
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    if (frameworkInitTimestampMicros != null) {
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      traceInfo['timeAfterFrameworkInitMicros'] = firstFrameBuiltTimestampMicros - frameworkInitTimestampMicros;
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    }
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  }

  traceInfoFile.writeAsStringSync(toPrettyJson(traceInfo));

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  logger.printStatus(message);
  logger.printStatus('Saved startup trace info in ${traceInfoFile.path}.');
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}