Initial flame_lua_runtime package

lib/runtime/resources/resource_load_limiter.dart

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+import 'dart:async' as async;
+import 'dart:collection';
+
+class ResourceLoadLimiter {
+  ResourceLoadLimiter(int maxConcurrent)
+    : maxConcurrent = _validateMaxConcurrent(maxConcurrent);
+
+  final int maxConcurrent;
+  final Queue<_QueuedLoadBase> _queue = Queue<_QueuedLoadBase>();
+  var _active = 0;
+
+  int get activeCount => _active;
+
+  int get pendingCount => _queue.length;
+
+  Future<T> run<T>(Future<T> Function() task) {
+    final queued = _QueuedLoad<T>(task);
+    _queue.add(queued);
+    _pump();
+    return queued.completer.future;
+  }
+
+  void clearPending() {
+    while (_queue.isNotEmpty) {
+      _queue.removeFirst().cancel();
+    }
+  }
+
+  void _pump() {
+    while (_active < maxConcurrent && _queue.isNotEmpty) {
+      final queued = _queue.removeFirst();
+      _active++;
+      async.unawaited(_runQueued(queued));
+    }
+  }
+
+  Future<void> _runQueued(_QueuedLoadBase queued) async {
+    try {
+      await queued.run();
+    } finally {
+      _active--;
+      _pump();
+    }
+  }
+
+  static int _validateMaxConcurrent(int value) {
+    if (value < 1) {
+      throw ArgumentError.value(value, 'maxConcurrent', 'must be >= 1');
+    }
+    return value;
+  }
+}
+
+abstract class _QueuedLoadBase {
+  Future<void> run();
+
+  void cancel();
+}
+
+class _QueuedLoad<T> implements _QueuedLoadBase {
+  _QueuedLoad(this._task);
+
+  final Future<T> Function() _task;
+  final completer = async.Completer<T>();
+
+  @override
+  Future<void> run() async {
+    if (completer.isCompleted) {
+      return;
+    }
+    try {
+      completer.complete(await _task());
+    } catch (error, stackTrace) {
+      completer.completeError(error, stackTrace);
+    }
+  }
+
+  @override
+  void cancel() {
+    if (!completer.isCompleted) {
+      completer.completeError(const ResourceLoadCancelledException());
+    }
+  }
+}
+
+class ResourceLoadCancelledException implements Exception {
+  const ResourceLoadCancelledException();
+
+  @override
+  String toString() => 'ResourceLoadCancelledException';
+}