perf: improved task pause/resume

lib/image_providers/thumbnail_provider.dart

@@ -21,7 +21,7 @@ class ThumbnailProvider extends ImageProvider<ThumbnailProviderKey> {
   ImageStreamCompleter load(ThumbnailProviderKey key, DecoderCallback decode) {
     return MultiFrameImageStreamCompleter(
       codec: _loadAsync(key, decode),
-      scale: key.scale,
+      scale: 1.0,
       informationCollector: () sync* {
         yield ErrorDescription('uri=${key.uri}, pageId=${key.pageId}, mimeType=${key.mimeType}, extent=${key.extent}');
       },
@@ -69,7 +69,7 @@ class ThumbnailProviderKey {
   final int pageId, rotationDegrees;
   final bool isFlipped;
   final int dateModifiedSecs;
-  final double extent, scale;
+  final double extent;
 
   const ThumbnailProviderKey({
     @required this.uri,
@@ -79,33 +79,27 @@ class ThumbnailProviderKey {
     @required this.isFlipped,
     @required this.dateModifiedSecs,
     this.extent = 0,
-    this.scale = 1,
   })  : assert(uri != null),
         assert(mimeType != null),
         assert(rotationDegrees != null),
         assert(isFlipped != null),
         assert(dateModifiedSecs != null),
-        assert(extent != null),
-        assert(scale != null);
+        assert(extent != null);
 
   @override
   bool operator ==(Object other) {
     if (other.runtimeType != runtimeType) return false;
-    return other is ThumbnailProviderKey && other.uri == uri && other.mimeType == mimeType && other.pageId == pageId && other.rotationDegrees == rotationDegrees && other.isFlipped == isFlipped && other.dateModifiedSecs == dateModifiedSecs && other.extent == extent && other.scale == scale;
+    return other is ThumbnailProviderKey && other.uri == uri && other.pageId == pageId && other.dateModifiedSecs == dateModifiedSecs && other.extent == extent;
   }
 
   @override
   int get hashCode => hashValues(
         uri,
-        mimeType,
         pageId,
-        rotationDegrees,
-        isFlipped,
         dateModifiedSecs,
         extent,
-        scale,
       );
 
   @override
-  String toString() => '$runtimeType#${shortHash(this)}{uri=$uri, mimeType=$mimeType, pageId=$pageId, rotationDegrees=$rotationDegrees, isFlipped=$isFlipped, dateModifiedSecs=$dateModifiedSecs, extent=$extent, scale=$scale}';
+  String toString() => '$runtimeType#${shortHash(this)}{uri=$uri, mimeType=$mimeType, pageId=$pageId, rotationDegrees=$rotationDegrees, isFlipped=$isFlipped, dateModifiedSecs=$dateModifiedSecs, extent=$extent}';
 }

lib/services/image_file_service.dart

@@ -204,7 +204,6 @@ class ImageFileService {
         }
         return null;
       },
-//      debugLabel: 'getThumbnail width=$width, height=$height entry=${entry.filenameWithoutExtension}',
       priority: priority ?? (extent == 0 ? ServiceCallPriority.getFastThumbnail : ServiceCallPriority.getSizedThumbnail),
       key: taskKey,
     );

lib/services/service_policy.dart

@@ -9,8 +9,8 @@ final ServicePolicy servicePolicy = ServicePolicy._private();
 class ServicePolicy {
   final StreamController<QueueState> _queueStreamController = StreamController<QueueState>.broadcast();
   final Map<Object, Tuple2<int, _Task>> _paused = {};
-  final SplayTreeMap<int, Queue<_Task>> _queues = SplayTreeMap();
-  final Queue<_Task> _runningQueue = Queue();
+  final SplayTreeMap<int, LinkedHashMap<Object, _Task>> _queues = SplayTreeMap();
+  final LinkedHashMap<Object, _Task> _runningQueue = LinkedHashMap();
 
   // magic number
   static const concurrentTaskMax = 4;
@@ -22,57 +22,59 @@ class ServicePolicy {
   Future<T> call<T>(
     Future<T> Function() platformCall, {
     int priority = ServiceCallPriority.normal,
-    String debugLabel,
     Object key,
   }) {
+    Completer<T> completer;
     _Task task;
     key ??= platformCall.hashCode;
-    final priorityTask = _paused.remove(key);
-    if (priorityTask != null) {
-      debugPrint('resume task with key=$key');
-      priority = priorityTask.item1;
-      task = priorityTask.item2;
+    final toResume = _paused.remove(key);
+    if (toResume != null) {
+      priority = toResume.item1;
+      task = toResume.item2;
+      completer = task.completer;
+    } else {
+      completer = Completer<T>();
+      task = _Task(
+        () async {
+          try {
+            completer.complete(await platformCall());
+          } catch (error, stackTrace) {
+            completer.completeError(error, stackTrace);
+          }
+          _runningQueue.remove(key);
+          _pickNext();
+        },
+        completer,
+      );
     }
-    var completer = task?.completer ?? Completer<T>();
-    task ??= _Task(
-      () async {
-        if (debugLabel != null) debugPrint('$runtimeType $debugLabel start');
-        try {
-          completer.complete(await platformCall());
-        } catch (error, stackTrace) {
-          completer.completeError(error, stackTrace);
-        }
-        if (debugLabel != null) debugPrint('$runtimeType $debugLabel completed');
-        _runningQueue.removeWhere((task) => task.key == key);
-        _pickNext();
-      },
-      completer,
-      key,
-    );
-    _getQueue(priority).addLast(task);
+    _getQueue(priority)[key] = task;
     _pickNext();
     return completer.future;
   }
 
   Future<T> resume<T>(Object key) {
-    final priorityTask = _paused.remove(key);
-    if (priorityTask == null) return null;
-    final priority = priorityTask.item1;
-    final task = priorityTask.item2;
-    _getQueue(priority).addLast(task);
-    _pickNext();
-    return task.completer.future;
+    final toResume = _paused.remove(key);
+    if (toResume != null) {
+      final priority = toResume.item1;
+      final task = toResume.item2;
+      _getQueue(priority)[key] = task;
+      _pickNext();
+      return task.completer.future;
+    } else {
+      return null;
+    }
   }
 
-  Queue<_Task> _getQueue(int priority) => _queues.putIfAbsent(priority, () => Queue<_Task>());
+  LinkedHashMap<Object, _Task> _getQueue(int priority) => _queues.putIfAbsent(priority, () => LinkedHashMap());
 
   void _pickNext() {
     _notifyQueueState();
     if (_runningQueue.length >= concurrentTaskMax) return;
     final queue = _queues.entries.firstWhere((kv) => kv.value.isNotEmpty, orElse: () => null)?.value;
-    final task = queue?.removeFirst();
-    if (task != null) {
-      _runningQueue.addLast(task);
+    if (queue != null && queue.isNotEmpty) {
+      final key = queue.keys.first;
+      final task = queue.remove(key);
+      _runningQueue[key] = task;
       task.callback();
     }
   }
@@ -80,14 +82,11 @@ class ServicePolicy {
   bool _takeOut(Object key, Iterable<int> priorities, void Function(int priority, _Task task) action) {
     var out = false;
     priorities.forEach((priority) {
-      final queue = _getQueue(priority);
-      final tasks = queue.where((task) => task.key == key).toList();
-      tasks.forEach((task) {
-        if (queue.remove(task)) {
-          out = true;
-          action(priority, task);
-        }
-      });
+      final task = _getQueue(priority).remove(key);
+      if (task != null) {
+        out = true;
+        action(priority, task);
+      }
     });
     return out;
   }
@@ -106,16 +105,15 @@ class ServicePolicy {
     if (!_queueStreamController.hasListener) return;
 
     final queueByPriority = Map.fromEntries(_queues.entries.map((kv) => MapEntry(kv.key, kv.value.length)));
-    _queueStreamController.add(QueueState(queueByPriority, _runningQueue.length));
+    _queueStreamController.add(QueueState(queueByPriority, _runningQueue.length, _paused.length));
   }
 }
 
 class _Task {
   final VoidCallback callback;
   final Completer completer;
-  final Object key;
 
-  const _Task(this.callback, this.completer, this.key);
+  const _Task(this.callback, this.completer);
 }
 
 class CancelledException {}
@@ -131,7 +129,7 @@ class ServiceCallPriority {
 
 class QueueState {
   final Map<int, int> queueByPriority;
-  final int runningQueue;
+  final int runningCount, pausedCount;
 
-  const QueueState(this.queueByPriority, this.runningQueue);
+  const QueueState(this.queueByPriority, this.runningCount, this.pausedCount);
 }

lib/widgets/debug/overlay.dart

@@ -24,7 +24,8 @@ class DebugTaskQueueOverlay extends StatelessWidget {
                     final queuedEntries = <MapEntry<dynamic, int>>[];
                     if (snapshot.hasData) {
                       final state = snapshot.data;
-                      queuedEntries.add(MapEntry('run', state.runningQueue));
+                      queuedEntries.add(MapEntry('run', state.runningCount));
+                      queuedEntries.add(MapEntry('paused', state.pausedCount));
                       queuedEntries.addAll(state.queueByPriority.entries.map((kv) => MapEntry(kv.key.toString(), kv.value)));
                     }
                     queuedEntries.sort((a, b) => a.key.compareTo(b.key));