| // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file |
| // for details. 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:async'; |
| |
| import 'package:async/async.dart'; |
| |
| import 'utils.dart'; |
| |
| /// An asynchronous operation that can be cancelled. |
| /// |
| /// The value of this operation is exposed as [value]. When this operation is |
| /// cancelled, [value] won't complete either successfully or with an error. If |
| /// [value] has already completed, cancelling the operation does nothing. |
| class CancelableOperation<T> { |
| /// The completer that produced this operation. |
| /// |
| /// This is canceled when [cancel] is called. |
| final CancelableCompleter<T> _completer; |
| |
| CancelableOperation._(this._completer); |
| |
| /// Creates a [CancelableOperation] wrapping [inner]. |
| /// |
| /// When this operation is canceled, [onCancel] will be called and any value |
| /// or error produced by [inner] will be discarded. If [onCancel] returns a |
| /// [Future], it will be forwarded to [cancel]. |
| /// |
| /// [onCancel] will be called synchronously when the operation is canceled. |
| /// It's guaranteed to only be called once. |
| /// |
| /// Calling this constructor is equivalent to creating a [CancelableCompleter] |
| /// and completing it with [inner]. As such, [isCompleted] is true from the |
| /// moment this [CancelableOperation] is created, regardless of whether |
| /// [inner] has completed yet or not. |
| factory CancelableOperation.fromFuture(Future<T> inner, |
| {FutureOr Function()? onCancel}) { |
| var completer = CancelableCompleter<T>(onCancel: onCancel); |
| completer.complete(inner); |
| return completer.operation; |
| } |
| |
| /// The value returned by the operation. |
| Future<T> get value => _completer._inner.future; |
| |
| /// Creates a [Stream] containing the result of this operation. |
| /// |
| /// This is like `value.asStream()`, but if a subscription to the stream is |
| /// canceled, this is as well. |
| Stream<T> asStream() { |
| var controller = |
| StreamController<T>(sync: true, onCancel: _completer._cancel); |
| |
| value.then((value) { |
| controller.add(value); |
| controller.close(); |
| }, onError: (Object error, StackTrace stackTrace) { |
| controller.addError(error, stackTrace); |
| controller.close(); |
| }); |
| return controller.stream; |
| } |
| |
| /// Creates a [Future] that completes when this operation completes *or* when |
| /// it's cancelled. |
| /// |
| /// If this operation completes, this completes to the same result as [value]. |
| /// If this operation is cancelled, the returned future waits for the future |
| /// returned by [cancel], then completes to [cancellationValue]. |
| Future<T?> valueOrCancellation([T? cancellationValue]) { |
| var completer = Completer<T?>.sync(); |
| value.then((result) => completer.complete(result), |
| onError: completer.completeError); |
| |
| _completer._cancelMemo.future.then((_) { |
| completer.complete(cancellationValue); |
| }, onError: completer.completeError); |
| |
| return completer.future; |
| } |
| |
| /// Registers callbacks to be called when this operation completes. |
| /// |
| /// [onValue] and [onError] behave in the same way as [Future.then]. |
| /// |
| /// If [onCancel] is provided, and this operation is canceled, the [onCancel] |
| /// callback is called and the returned operation completes with the result. |
| /// |
| /// If [onCancel] is not given, and this operation is canceled, then the |
| /// returned operation is canceled. |
| /// |
| /// If [propagateCancel] is `true` and the returned operation is canceled then |
| /// this operation is canceled. The default is `false`. |
| CancelableOperation<R> then<R>(FutureOr<R> Function(T) onValue, |
| {FutureOr<R> Function(Object, StackTrace)? onError, |
| FutureOr<R> Function()? onCancel, |
| bool propagateCancel = false}) { |
| final completer = |
| CancelableCompleter<R>(onCancel: propagateCancel ? cancel : null); |
| |
| valueOrCancellation().then((T? result) { |
| if (!completer.isCanceled) { |
| if (isCompleted) { |
| assert(result is T); |
| completer.complete(Future.sync(() => onValue(result!))); |
| } else if (onCancel != null) { |
| completer.complete(Future.sync(onCancel)); |
| } else { |
| completer._cancel(); |
| } |
| } |
| }, onError: (Object error, StackTrace stackTrace) { |
| if (!completer.isCanceled) { |
| if (onError != null) { |
| completer.complete(Future.sync(() => onError(error, stackTrace))); |
| } else { |
| completer.completeError(error, stackTrace); |
| } |
| } |
| }); |
| return completer.operation; |
| } |
| |
| /// Cancels this operation. |
| /// |
| /// This returns the [Future] returned by the [CancelableCompleter]'s |
| /// `onCancel` callback. Unlike [Stream.cancel], it never returns `null`. |
| Future cancel() => _completer._cancel(); |
| |
| /// Whether this operation has been canceled before it completed. |
| bool get isCanceled => _completer.isCanceled; |
| |
| /// Whether the [CancelableCompleter] backing this operation has been |
| /// completed. |
| /// |
| /// This value being true does not imply that the [value] future has |
| /// completed, but merely that it is no longer possible to [cancel] the |
| /// operation. |
| bool get isCompleted => _completer.isCompleted; |
| } |
| |
| /// A completer for a [CancelableOperation]. |
| class CancelableCompleter<T> { |
| /// The completer for the wrapped future. |
| final Completer<T> _inner; |
| |
| /// The callback to call if the future is canceled. |
| final FutureOrCallback? _onCancel; |
| |
| /// Creates a new completer for a [CancelableOperation]. |
| /// |
| /// When the future operation canceled, as long as the completer hasn't yet |
| /// completed, [onCancel] is called. If [onCancel] returns a [Future], it's |
| /// forwarded to [CancelableOperation.cancel]. |
| /// |
| /// [onCancel] will be called synchronously when the operation is canceled. |
| /// It's guaranteed to only be called once. |
| CancelableCompleter({FutureOr Function()? onCancel}) |
| : _onCancel = onCancel, |
| _inner = Completer<T>() { |
| operation = CancelableOperation<T>._(this); |
| } |
| |
| /// The operation controlled by this completer. |
| late final CancelableOperation<T> operation; |
| |
| /// Whether the completer has completed. |
| bool get isCompleted => _isCompleted; |
| bool _isCompleted = false; |
| |
| /// Whether the completer was canceled before being completed. |
| bool get isCanceled => _isCanceled; |
| bool _isCanceled = false; |
| |
| /// The memoizer for [_cancel]. |
| final _cancelMemo = AsyncMemoizer(); |
| |
| /// Completes [operation] to [value]. |
| /// |
| /// If [value] is a [Future], this will complete to the result of that |
| /// [Future] once it completes. |
| void complete([FutureOr<T>? value]) { |
| if (_isCompleted) throw StateError('Operation already completed'); |
| _isCompleted = true; |
| |
| if (value is! Future) { |
| if (_isCanceled) return; |
| _inner.complete(value); |
| return; |
| } |
| |
| final future = value as Future<T>; |
| if (_isCanceled) { |
| // Make sure errors from [value] aren't top-leveled. |
| future.catchError((_) {}); |
| return; |
| } |
| |
| future.then((result) { |
| if (_isCanceled) return; |
| _inner.complete(result); |
| }, onError: (Object error, StackTrace stackTrace) { |
| if (_isCanceled) return; |
| _inner.completeError(error, stackTrace); |
| }); |
| } |
| |
| /// Completes [operation] to [error]. |
| void completeError(Object error, [StackTrace? stackTrace]) { |
| if (_isCompleted) throw StateError('Operation already completed'); |
| _isCompleted = true; |
| |
| if (_isCanceled) return; |
| _inner.completeError(error, stackTrace); |
| } |
| |
| /// Cancel the completer. |
| Future _cancel() { |
| if (_inner.isCompleted) return Future.value(); |
| |
| return _cancelMemo.runOnce(() { |
| _isCanceled = true; |
| var onCancel = _onCancel; |
| if (onCancel != null) return onCancel(); |
| }); |
| } |
| } |