putIfAbsent method Null safety

Implementation

ImageStreamCompleter? putIfAbsent(Object key, ImageStreamCompleter Function() loader, { ImageErrorListener? onError }) {
  assert(key != null);
  assert(loader != null);
  TimelineTask? timelineTask;
  TimelineTask? listenerTask;
  if (!kReleaseMode) {
    timelineTask = TimelineTask()..start(
      'ImageCache.putIfAbsent',
      arguments: <String, dynamic>{
        'key': key.toString(),
      },
    );
  }
  ImageStreamCompleter? result = _pendingImages[key]?.completer;
  // Nothing needs to be done because the image hasn't loaded yet.
  if (result != null) {
    if (!kReleaseMode) {
      timelineTask!.finish(arguments: <String, dynamic>{'result': 'pending'});
    }
    return result;
  }
  // Remove the provider from the list so that we can move it to the
  // recently used position below.
  // Don't use _touch here, which would trigger a check on cache size that is
  // not needed since this is just moving an existing cache entry to the head.
  final _CachedImage? image = _cache.remove(key);
  if (image != null) {
    if (!kReleaseMode) {
      timelineTask!.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
    }
    // The image might have been keptAlive but had no listeners (so not live).
    // Make sure the cache starts tracking it as live again.
    _trackLiveImage(
      key,
      image.completer,
      image.sizeBytes,
    );
    _cache[key] = image;
    return image.completer;
  }

  final _LiveImage? liveImage = _liveImages[key];
  if (liveImage != null) {
    _touch(
      key,
      _CachedImage(
        liveImage.completer,
        sizeBytes: liveImage.sizeBytes,
      ),
      timelineTask,
    );
    if (!kReleaseMode) {
      timelineTask!.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
    }
    return liveImage.completer;
  }

  try {
    result = loader();
    _trackLiveImage(key, result, null);
  } catch (error, stackTrace) {
    if (!kReleaseMode) {
      timelineTask!.finish(arguments: <String, dynamic>{
        'result': 'error',
        'error': error.toString(),
        'stackTrace': stackTrace.toString(),
      });
    }
    if (onError != null) {
      onError(error, stackTrace);
      return null;
    } else {
      rethrow;
    }
  }

  if (!kReleaseMode) {
    listenerTask = TimelineTask(parent: timelineTask)..start('listener');
  }
  // A multi-frame provider may call the listener more than once. We need do make
  // sure that some cleanup works won't run multiple times, such as finishing the
  // tracing task or removing the listeners
  bool listenedOnce = false;

  // We shouldn't use the _pendingImages map if the cache is disabled, but we
  // will have to listen to the image at least once so we don't leak it in
  // the live image tracking.
  final bool trackPendingImage = maximumSize > 0 && maximumSizeBytes > 0;
  late _PendingImage pendingImage;
  void listener(ImageInfo? info, bool syncCall) {
    int? sizeBytes;
    if (info != null) {
      sizeBytes = info.sizeBytes;
      info.dispose();
    }
    final _CachedImage image = _CachedImage(
      result!,
      sizeBytes: sizeBytes,
    );

    _trackLiveImage(key, result, sizeBytes);

    // Only touch if the cache was enabled when resolve was initially called.
    if (trackPendingImage) {
      _touch(key, image, listenerTask);
    } else {
      image.dispose();
    }

    _pendingImages.remove(key);
    if (!listenedOnce) {
      pendingImage.removeListener();
    }
    if (!kReleaseMode && !listenedOnce) {
      listenerTask!.finish(arguments: <String, dynamic>{
        'syncCall': syncCall,
        'sizeInBytes': sizeBytes,
      });
      timelineTask!.finish(arguments: <String, dynamic>{
        'currentSizeBytes': currentSizeBytes,
        'currentSize': currentSize,
      });
    }
    listenedOnce = true;
  }

  final ImageStreamListener streamListener = ImageStreamListener(listener);
  pendingImage = _PendingImage(result, streamListener);
  if (trackPendingImage) {
    _pendingImages[key] = pendingImage;
  }
  // Listener is removed in [_PendingImage.removeListener].
  result.addListener(streamListener);

  return result;
}