| // Copyright 2014 The Flutter Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| import 'dart:developer'; |
| import 'dart:ui' show hashValues; |
| |
| import 'package:flutter/foundation.dart'; |
| |
| import 'image_stream.dart'; |
| |
| const int _kDefaultSize = 1000; |
| const int _kDefaultSizeBytes = 100 << 20; // 100 MiB |
| |
| /// Class for caching images. |
| /// |
| /// Implements a least-recently-used cache of up to 1000 images, and up to 100 |
| /// MB. The maximum size can be adjusted using [maximumSize] and |
| /// [maximumSizeBytes]. |
| /// |
| /// The cache also holds a list of "live" references. An image is considered |
| /// live if its [ImageStreamCompleter]'s listener count has never dropped to |
| /// zero after adding at least one listener. The cache uses |
| /// [ImageStreamCompleter.addOnLastListenerRemovedCallback] to determine when |
| /// this has happened. |
| /// |
| /// The [putIfAbsent] method is the main entry-point to the cache API. It |
| /// returns the previously cached [ImageStreamCompleter] for the given key, if |
| /// available; if not, it calls the given callback to obtain it first. In either |
| /// case, the key is moved to the "most recently used" position. |
| /// |
| /// A caller can determine whether an image is already in the cache by using |
| /// [containsKey], which will return true if the image is tracked by the cache |
| /// in a pending or completed state. More fine grained information is available |
| /// by using the [statusForKey] method. |
| /// |
| /// Generally this class is not used directly. The [ImageProvider] class and its |
| /// subclasses automatically handle the caching of images. |
| /// |
| /// A shared instance of this cache is retained by [PaintingBinding] and can be |
| /// obtained via the [imageCache] top-level property in the [painting] library. |
| /// |
| /// {@tool snippet} |
| /// |
| /// This sample shows how to supply your own caching logic and replace the |
| /// global [imageCache] variable. |
| /// |
| /// ```dart |
| /// /// This is the custom implementation of [ImageCache] where we can override |
| /// /// the logic. |
| /// class MyImageCache extends ImageCache { |
| /// @override |
| /// void clear() { |
| /// print("Clearing cache!"); |
| /// super.clear(); |
| /// } |
| /// } |
| /// |
| /// class MyWidgetsBinding extends WidgetsFlutterBinding { |
| /// @override |
| /// ImageCache createImageCache() => MyImageCache(); |
| /// } |
| /// |
| /// void main() { |
| /// // The constructor sets global variables. |
| /// MyWidgetsBinding(); |
| /// runApp(MyApp()); |
| /// } |
| /// |
| /// class MyApp extends StatelessWidget { |
| /// @override |
| /// Widget build(BuildContext context) { |
| /// return Container(); |
| /// } |
| /// } |
| /// ``` |
| /// {@end-tool} |
| class ImageCache { |
| final Map<Object, _PendingImage> _pendingImages = <Object, _PendingImage>{}; |
| final Map<Object, _CachedImage> _cache = <Object, _CachedImage>{}; |
| /// ImageStreamCompleters with at least one listener. These images may or may |
| /// not fit into the _pendingImages or _cache objects. |
| /// |
| /// Unlike _cache, the [_CachedImage] for this may have a null byte size. |
| final Map<Object, _LiveImage> _liveImages = <Object, _LiveImage>{}; |
| |
| /// Maximum number of entries to store in the cache. |
| /// |
| /// Once this many entries have been cached, the least-recently-used entry is |
| /// evicted when adding a new entry. |
| int get maximumSize => _maximumSize; |
| int _maximumSize = _kDefaultSize; |
| /// Changes the maximum cache size. |
| /// |
| /// If the new size is smaller than the current number of elements, the |
| /// extraneous elements are evicted immediately. Setting this to zero and then |
| /// returning it to its original value will therefore immediately clear the |
| /// cache. |
| set maximumSize(int value) { |
| assert(value != null); |
| assert(value >= 0); |
| if (value == maximumSize) |
| return; |
| TimelineTask? timelineTask; |
| if (!kReleaseMode) { |
| timelineTask = TimelineTask()..start( |
| 'ImageCache.setMaximumSize', |
| arguments: <String, dynamic>{'value': value}, |
| ); |
| } |
| _maximumSize = value; |
| if (maximumSize == 0) { |
| clear(); |
| } else { |
| _checkCacheSize(timelineTask); |
| } |
| if (!kReleaseMode) { |
| timelineTask!.finish(); |
| } |
| } |
| |
| /// The current number of cached entries. |
| int get currentSize => _cache.length; |
| |
| /// Maximum size of entries to store in the cache in bytes. |
| /// |
| /// Once more than this amount of bytes have been cached, the |
| /// least-recently-used entry is evicted until there are fewer than the |
| /// maximum bytes. |
| int get maximumSizeBytes => _maximumSizeBytes; |
| int _maximumSizeBytes = _kDefaultSizeBytes; |
| /// Changes the maximum cache bytes. |
| /// |
| /// If the new size is smaller than the current size in bytes, the |
| /// extraneous elements are evicted immediately. Setting this to zero and then |
| /// returning it to its original value will therefore immediately clear the |
| /// cache. |
| set maximumSizeBytes(int value) { |
| assert(value != null); |
| assert(value >= 0); |
| if (value == _maximumSizeBytes) |
| return; |
| TimelineTask? timelineTask; |
| if (!kReleaseMode) { |
| timelineTask = TimelineTask()..start( |
| 'ImageCache.setMaximumSizeBytes', |
| arguments: <String, dynamic>{'value': value}, |
| ); |
| } |
| _maximumSizeBytes = value; |
| if (_maximumSizeBytes == 0) { |
| clear(); |
| } else { |
| _checkCacheSize(timelineTask); |
| } |
| if (!kReleaseMode) { |
| timelineTask!.finish(); |
| } |
| } |
| |
| /// The current size of cached entries in bytes. |
| int get currentSizeBytes => _currentSizeBytes; |
| int _currentSizeBytes = 0; |
| |
| /// Evicts all pending and keepAlive entries from the cache. |
| /// |
| /// This is useful if, for instance, the root asset bundle has been updated |
| /// and therefore new images must be obtained. |
| /// |
| /// Images which have not finished loading yet will not be removed from the |
| /// cache, and when they complete they will be inserted as normal. |
| /// |
| /// This method does not clear live references to images, since clearing those |
| /// would not reduce memory pressure. Such images still have listeners in the |
| /// application code, and will still remain resident in memory. |
| /// |
| /// To clear live references, use [clearLiveImages]. |
| void clear() { |
| if (!kReleaseMode) { |
| Timeline.instantSync( |
| 'ImageCache.clear', |
| arguments: <String, dynamic>{ |
| 'pendingImages': _pendingImages.length, |
| 'keepAliveImages': _cache.length, |
| 'liveImages': _liveImages.length, |
| 'currentSizeInBytes': _currentSizeBytes, |
| }, |
| ); |
| } |
| _cache.clear(); |
| _pendingImages.clear(); |
| _currentSizeBytes = 0; |
| } |
| |
| /// Evicts a single entry from the cache, returning true if successful. |
| /// |
| /// Pending images waiting for completion are removed as well, returning true |
| /// if successful. When a pending image is removed the listener on it is |
| /// removed as well to prevent it from adding itself to the cache if it |
| /// eventually completes. |
| /// |
| /// If this method removes a pending image, it will also remove |
| /// the corresponding live tracking of the image, since it is no longer clear |
| /// if the image will ever complete or have any listeners, and failing to |
| /// remove the live reference could leave the cache in a state where all |
| /// subsequent calls to [putIfAbsent] will return an [ImageStreamCompleter] |
| /// that will never complete. |
| /// |
| /// If this method removes a completed image, it will _not_ remove the live |
| /// reference to the image, which will only be cleared when the listener |
| /// count on the completer drops to zero. To clear live image references, |
| /// whether completed or not, use [clearLiveImages]. |
| /// |
| /// The `key` must be equal to an object used to cache an image in |
| /// [ImageCache.putIfAbsent]. |
| /// |
| /// If the key is not immediately available, as is common, consider using |
| /// [ImageProvider.evict] to call this method indirectly instead. |
| /// |
| /// The `includeLive` argument determines whether images that still have |
| /// listeners in the tree should be evicted as well. This parameter should be |
| /// set to true in cases where the image may be corrupted and needs to be |
| /// completely discarded by the cache. It should be set to false when calls |
| /// to evict are trying to relieve memory pressure, since an image with a |
| /// listener will not actually be evicted from memory, and subsequent attempts |
| /// to load it will end up allocating more memory for the image again. The |
| /// argument must not be null. |
| /// |
| /// See also: |
| /// |
| /// * [ImageProvider], for providing images to the [Image] widget. |
| bool evict(Object key, { bool includeLive = true }) { |
| assert(includeLive != null); |
| if (includeLive) { |
| // Remove from live images - the cache will not be able to mark |
| // it as complete, and it might be getting evicted because it |
| // will never complete, e.g. it was loaded in a FakeAsync zone. |
| // In such a case, we need to make sure subsequent calls to |
| // putIfAbsent don't return this image that may never complete. |
| final _LiveImage? image = _liveImages.remove(key); |
| image?.removeListener(); |
| } |
| final _PendingImage? pendingImage = _pendingImages.remove(key); |
| if (pendingImage != null) { |
| if (!kReleaseMode) { |
| Timeline.instantSync('ImageCache.evict', arguments: <String, dynamic>{ |
| 'type': 'pending' |
| }); |
| } |
| pendingImage.removeListener(); |
| return true; |
| } |
| final _CachedImage? image = _cache.remove(key); |
| if (image != null) { |
| if (!kReleaseMode) { |
| Timeline.instantSync('ImageCache.evict', arguments: <String, dynamic>{ |
| 'type': 'keepAlive', |
| 'sizeInBytes': image.sizeBytes, |
| }); |
| } |
| _currentSizeBytes -= image.sizeBytes!; |
| return true; |
| } |
| if (!kReleaseMode) { |
| Timeline.instantSync('ImageCache.evict', arguments: <String, dynamic>{ |
| 'type': 'miss', |
| }); |
| } |
| return false; |
| } |
| |
| /// Updates the least recently used image cache with this image, if it is |
| /// less than the [maximumSizeBytes] of this cache. |
| /// |
| /// Resizes the cache as appropriate to maintain the constraints of |
| /// [maximumSize] and [maximumSizeBytes]. |
| void _touch(Object key, _CachedImage image, TimelineTask? timelineTask) { |
| assert(timelineTask != null); |
| if (image.sizeBytes != null && image.sizeBytes! <= maximumSizeBytes) { |
| _currentSizeBytes += image.sizeBytes!; |
| _cache[key] = image; |
| _checkCacheSize(timelineTask); |
| } |
| } |
| |
| void _trackLiveImage(Object key, _LiveImage image) { |
| // Avoid adding unnecessary callbacks to the completer. |
| _liveImages.putIfAbsent(key, () { |
| // Even if no callers to ImageProvider.resolve have listened to the stream, |
| // the cache is listening to the stream and will remove itself once the |
| // image completes to move it from pending to keepAlive. |
| // Even if the cache size is 0, we still add this listener. |
| image.completer.addOnLastListenerRemovedCallback(image.handleRemove); |
| return image; |
| }).sizeBytes ??= image.sizeBytes; |
| } |
| |
| /// Returns the previously cached [ImageStream] for the given key, if available; |
| /// if not, calls the given callback to obtain it first. In either case, the |
| /// key is moved to the "most recently used" position. |
| /// |
| /// The arguments must not be null. The `loader` cannot return null. |
| /// |
| /// In the event that the loader throws an exception, it will be caught only if |
| /// `onError` is also provided. When an exception is caught resolving an image, |
| /// no completers are cached and `null` is returned instead of a new |
| /// completer. |
| ImageStreamCompleter? putIfAbsent(Object key, ImageStreamCompleter 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, _LiveImage(image.completer, image.sizeBytes, () => _liveImages.remove(key))); |
| _cache[key] = image; |
| return image.completer; |
| } |
| |
| final _CachedImage? liveImage = _liveImages[key]; |
| if (liveImage != null) { |
| _touch(key, liveImage, timelineTask); |
| if (!kReleaseMode) { |
| timelineTask!.finish(arguments: <String, dynamic>{'result': 'keepAlive'}); |
| } |
| return liveImage.completer; |
| } |
| |
| try { |
| result = loader(); |
| _trackLiveImage(key, _LiveImage(result, null, () => _liveImages.remove(key))); |
| } 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'); |
| } |
| // If we're doing tracing, we need to make sure that we don't try to finish |
| // the trace entry multiple times if we get re-entrant calls from a multi- |
| // frame provider here. |
| 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. |
| // If the cache is disabled, this variable will be set. |
| _PendingImage? untrackedPendingImage; |
| void listener(ImageInfo? info, bool syncCall) { |
| // Images that fail to load don't contribute to cache size. |
| final int imageSize = info == null || info.image == null ? 0 : info.image.height * info.image.width * 4; |
| |
| final _CachedImage image = _CachedImage(result!, imageSize); |
| |
| _trackLiveImage( |
| key, |
| _LiveImage( |
| result, |
| imageSize, |
| () => _liveImages.remove(key), |
| ), |
| ); |
| |
| final _PendingImage? pendingImage = untrackedPendingImage ?? _pendingImages.remove(key); |
| if (pendingImage != null) { |
| pendingImage.removeListener(); |
| } |
| // Only touch if the cache was enabled when resolve was initially called. |
| if (untrackedPendingImage == null) { |
| _touch(key, image, listenerTask); |
| } |
| |
| if (!kReleaseMode && !listenedOnce) { |
| listenerTask!.finish(arguments: <String, dynamic>{ |
| 'syncCall': syncCall, |
| 'sizeInBytes': imageSize, |
| }); |
| timelineTask!.finish(arguments: <String, dynamic>{ |
| 'currentSizeBytes': currentSizeBytes, |
| 'currentSize': currentSize, |
| }); |
| } |
| listenedOnce = true; |
| } |
| |
| final ImageStreamListener streamListener = ImageStreamListener(listener); |
| if (maximumSize > 0 && maximumSizeBytes > 0) { |
| _pendingImages[key] = _PendingImage(result, streamListener); |
| } else { |
| untrackedPendingImage = _PendingImage(result, streamListener); |
| } |
| // Listener is removed in [_PendingImage.removeListener]. |
| result.addListener(streamListener); |
| |
| return result; |
| } |
| |
| /// The [ImageCacheStatus] information for the given `key`. |
| ImageCacheStatus statusForKey(Object key) { |
| return ImageCacheStatus._( |
| pending: _pendingImages.containsKey(key), |
| keepAlive: _cache.containsKey(key), |
| live: _liveImages.containsKey(key), |
| ); |
| } |
| |
| /// Returns whether this `key` has been previously added by [putIfAbsent]. |
| bool containsKey(Object key) { |
| return _pendingImages[key] != null || _cache[key] != null; |
| } |
| |
| /// The number of live images being held by the [ImageCache]. |
| /// |
| /// Compare with [ImageCache.currentSize] for keepAlive images. |
| int get liveImageCount => _liveImages.length; |
| |
| /// The number of images being tracked as pending in the [ImageCache]. |
| /// |
| /// Compare with [ImageCache.currentSize] for keepAlive images. |
| int get pendingImageCount => _pendingImages.length; |
| |
| /// Clears any live references to images in this cache. |
| /// |
| /// An image is considered live if its [ImageStreamCompleter] has never hit |
| /// zero listeners after adding at least one listener. The |
| /// [ImageStreamCompleter.addOnLastListenerRemovedCallback] is used to |
| /// determine when this has happened. |
| /// |
| /// This is called after a hot reload to evict any stale references to image |
| /// data for assets that have changed. Calling this method does not relieve |
| /// memory pressure, since the live image caching only tracks image instances |
| /// that are also being held by at least one other object. |
| void clearLiveImages() { |
| for (final _LiveImage image in _liveImages.values) { |
| image.removeListener(); |
| } |
| _liveImages.clear(); |
| } |
| |
| // Remove images from the cache until both the length and bytes are below |
| // maximum, or the cache is empty. |
| void _checkCacheSize(TimelineTask? timelineTask) { |
| final Map<String, dynamic> finishArgs = <String, dynamic>{}; |
| TimelineTask? checkCacheTask; |
| if (!kReleaseMode) { |
| checkCacheTask = TimelineTask(parent: timelineTask)..start('checkCacheSize'); |
| finishArgs['evictedKeys'] = <String>[]; |
| finishArgs['currentSize'] = currentSize; |
| finishArgs['currentSizeBytes'] = currentSizeBytes; |
| } |
| while (_currentSizeBytes > _maximumSizeBytes || _cache.length > _maximumSize) { |
| final Object key = _cache.keys.first; |
| final _CachedImage image = _cache[key]!; |
| _currentSizeBytes -= image.sizeBytes!; |
| _cache.remove(key); |
| if (!kReleaseMode) { |
| finishArgs['evictedKeys'].add(key.toString()); |
| } |
| } |
| if (!kReleaseMode) { |
| finishArgs['endSize'] = currentSize; |
| finishArgs['endSizeBytes'] = currentSizeBytes; |
| checkCacheTask!.finish(arguments: finishArgs); |
| } |
| assert(_currentSizeBytes >= 0); |
| assert(_cache.length <= maximumSize); |
| assert(_currentSizeBytes <= maximumSizeBytes); |
| } |
| } |
| |
| /// Information about how the [ImageCache] is tracking an image. |
| /// |
| /// A [pending] image is one that has not completed yet. It may also be tracked |
| /// as [live] because something is listening to it. |
| /// |
| /// A [keepAlive] image is being held in the cache, which uses Least Recently |
| /// Used semantics to determine when to evict an image. These images are subject |
| /// to eviction based on [ImageCache.maximumSizeBytes] and |
| /// [ImageCache.maximumSize]. It may be [live], but not [pending]. |
| /// |
| /// A [live] image is being held until its [ImageStreamCompleter] has no more |
| /// listeners. It may also be [pending] or [keepAlive]. |
| /// |
| /// An [untracked] image is not being cached. |
| /// |
| /// To obtain an [ImageCacheStatus], use [ImageCache.statusForKey] or |
| /// [ImageProvider.obtainCacheStatus]. |
| @immutable |
| class ImageCacheStatus { |
| const ImageCacheStatus._({ |
| this.pending = false, |
| this.keepAlive = false, |
| this.live = false, |
| }) : assert(!pending || !keepAlive); |
| |
| /// An image that has been submitted to [ImageCache.putIfAbsent], but |
| /// not yet completed. |
| final bool pending; |
| |
| /// An image that has been submitted to [ImageCache.putIfAbsent], has |
| /// completed, fits based on the sizing rules of the cache, and has not been |
| /// evicted. |
| /// |
| /// Such images will be kept alive even if [live] is false, as long |
| /// as they have not been evicted from the cache based on its sizing rules. |
| final bool keepAlive; |
| |
| /// An image that has been submitted to [ImageCache.putIfAbsent] and has at |
| /// least one listener on its [ImageStreamCompleter]. |
| /// |
| /// Such images may also be [keepAlive] if they fit in the cache based on its |
| /// sizing rules. They may also be [pending] if they have not yet resolved. |
| final bool live; |
| |
| /// An image that is tracked in some way by the [ImageCache], whether |
| /// [pending], [keepAlive], or [live]. |
| bool get tracked => pending || keepAlive || live; |
| |
| /// An image that either has not been submitted to |
| /// [ImageCache.putIfAbsent] or has otherwise been evicted from the |
| /// [keepAlive] and [live] caches. |
| bool get untracked => !pending && !keepAlive && !live; |
| |
| @override |
| bool operator ==(Object other) { |
| if (other.runtimeType != runtimeType) { |
| return false; |
| } |
| return other is ImageCacheStatus |
| && other.pending == pending |
| && other.keepAlive == keepAlive |
| && other.live == live; |
| } |
| |
| @override |
| int get hashCode => hashValues(pending, keepAlive, live); |
| |
| @override |
| String toString() => '${objectRuntimeType(this, 'ImageCacheStatus')}(pending: $pending, live: $live, keepAlive: $keepAlive)'; |
| } |
| |
| class _CachedImage { |
| _CachedImage(this.completer, this.sizeBytes); |
| |
| final ImageStreamCompleter completer; |
| int? sizeBytes; |
| } |
| |
| class _LiveImage extends _CachedImage { |
| _LiveImage(ImageStreamCompleter completer, int? sizeBytes, this.handleRemove) |
| : super(completer, sizeBytes); |
| |
| final VoidCallback handleRemove; |
| |
| void removeListener() { |
| completer.removeOnLastListenerRemovedCallback(handleRemove); |
| } |
| } |
| |
| class _PendingImage { |
| _PendingImage(this.completer, this.listener); |
| |
| final ImageStreamCompleter completer; |
| final ImageStreamListener listener; |
| |
| void removeListener() { |
| completer.removeListener(listener); |
| } |
| } |