Index: lib/src/cancelable_operation.dart |
diff --git a/lib/src/cancelable_operation.dart b/lib/src/cancelable_operation.dart |
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+// 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. |
+ |
+library async.cancelable_operation; |
+ |
+import 'dart:async'; |
+ |
+import 'package:async/async.dart'; |
+ |
+/// An asynchronuos operation that can be cancelled. |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
So basically, you have the result of an async oper
nweiz
2015/08/28 00:34:56
All this is true, although CancelableCompleter is
|
+/// |
+/// 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; |
+ |
+ Future<T> get value => _completer._inner.future; |
Lasse Reichstein Nielsen
2015/08/27 10:20:53
I'd call this "result" since it may be an error. W
Lasse Reichstein Nielsen
2015/08/27 10:20:54
Move getter below constructor.
nweiz
2015/08/28 00:34:56
"result" seems confusing when the package has a "R
nweiz
2015/08/28 00:34:56
Done, although this is contrary to the style most
Lasse Reichstein Nielsen
2015/09/03 13:06:17
The order in the file is independent of how the AP
|
+ |
+ /// Whether this operation has been canceled. |
+ bool _canceled = false; |
+ |
+ CancelableOperation._(this._completer); |
Lasse Reichstein Nielsen
2015/08/27 10:57:41
I think one thing that makes it hard for me to wra
Lasse Reichstein Nielsen
2015/08/27 10:59:47
And it is, the other one was the cancelable comple
nweiz
2015/08/28 00:34:55
That's true, but I expect exposing operations crea
|
+ |
+ /// 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. The callback may return a |
+ /// Future to indicate that asynchronous work has to be done to cancel the |
+ /// future; this Future will be returned by [cancel]. |
+ factory CancelableOperation.fromFuture(Future<T> inner, {onCancel()}) { |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
Why is onCancel optional? If it's null, I don't se
nweiz
2015/08/28 00:34:56
From the user's perspective, canceling an operatio
Lasse Reichstein Nielsen
2015/09/03 13:06:17
Ack, makes sense. Cancel only cancels the "operati
|
+ var completer = new CancelableCompleter<T>(onCancel: onCancel); |
+ completer.complete(inner); |
+ return completer.operation; |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
You are passing a callback here, which is not goin
nweiz
2015/08/28 00:34:56
I don't think it's very likely that multiple dispa
Lasse Reichstein Nielsen
2015/09/03 13:06:17
True. It has to be documented when the callback wi
nweiz
2015/09/08 21:14:45
Done.
|
+ } |
+ |
+ /// 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() { |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
I prefer to make this a getter.
nweiz
2015/08/28 00:34:56
I think it's more important for it to be consisten
Lasse Reichstein Nielsen
2015/09/03 13:06:17
Ok, that's fair.
|
+ var controller = new StreamController<T>( |
+ sync: true, onCancel: _completer._cancel); |
+ |
+ value.then((value) { |
+ controller.add(value); |
+ controller.close(); |
+ }, onError: (error, stackTrace) { |
+ controller.addError(error, stackTrace); |
+ controller.close(); |
+ }); |
+ return controller.stream; |
+ } |
+ |
+ /// Cancels this operation. |
+ /// |
+ /// This returns the [Future] returned by the [CancelableCompleter]'s |
+ /// `onCancel` callback. Unlike [Stream.cancel], it never returns `null`. |
+ Future cancel() { |
+ _canceled = true; |
Lasse Reichstein Nielsen
2015/09/03 13:06:17
Maybe drop the _canceled field in this class and j
nweiz
2015/09/08 21:14:45
We don't actually use this field anyway, it turns
|
+ return _completer._cancel(); |
+ } |
+} |
+ |
+/// A completer for a [CancelableOperation]. |
+class CancelableCompleter<T> { |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
I don't think you need this class.
Do you *want* i
nweiz
2015/08/28 00:34:56
Yeah; see above comments.
|
+ /// The completer for the wrapped future. |
+ final Completer<T> _inner; |
+ |
+ /// The callback to call if the future is canceled. |
+ final ZoneCallback _onCancel; |
+ |
+ CancelableOperation<T> get operation => _operation; |
+ CancelableOperation<T> _operation; |
Lasse Reichstein Nielsen
2015/08/27 10:20:53
I find it very hard to see which fields the class
nweiz
2015/08/28 00:34:56
Done, although see above.
|
+ |
+ /// 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; |
+ |
+ /// Whether the completer has fired. |
+ /// |
+ /// This is distinct from [isCompleted] when a [Future] is passed to |
+ /// [complete]; this won't be `true` until that [Future] fires. |
+ bool _fired = false; |
Lasse Reichstein Nielsen
2015/09/03 13:06:17
I think _fired is equivalent to _inner.isCompleted
nweiz
2015/09/08 21:14:45
Done.
|
+ |
+ /// Creates a new completer for a [CancelableOperation]. |
+ /// |
+ /// When the future operation canceled, as long as the completer hasn't yet |
+ /// completed, [onCancel] is called. The callback may return a [Future]; if |
+ /// so, that [Future] is returned by [CancelableOperation.cancel]. |
+ CancelableCompleter({onCancel()}) |
+ : _onCancel = onCancel, |
+ _inner = new Completer<T>() { |
+ _operation = new CancelableOperation<T>._(this); |
+ } |
+ |
+ /// Completes [operation] to [value]. |
+ /// |
+ /// If [value] is a [Future], this will complete to the result of that |
+ /// [Future] once it completes. |
+ void complete([value]) { |
+ if (_isCompleted) throw new StateError("Operation already completed"); |
+ _isCompleted = true; |
+ |
+ if (_isCanceled) return; |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
If value is a future with an error, the error is n
nweiz
2015/08/28 00:34:56
Done.
|
+ if (value is! Future) { |
+ _fired = true; |
+ _inner.complete(value); |
+ return; |
+ } |
+ |
+ value.then((result) { |
+ if (_isCanceled) return; |
+ _fired = true; |
+ _inner.complete(result); |
+ }, onError: (error, stackTrace) { |
+ if (_isCanceled) return; |
+ _fired = true; |
+ _inner.completeError(error, stackTrace); |
+ }); |
+ } |
+ |
+ /// Completes [operation] to [error]. |
+ void completeError(Object error, [StackTrace stackTrace]) { |
+ if (_isCompleted) throw new StateError("Operation already completed"); |
+ _isCompleted = true; |
+ |
+ if (_isCanceled) return; |
+ _fired = true; |
+ _inner.completeError(error, stackTrace); |
+ } |
+ |
+ /// Cancel the completer. |
+ Future _cancel() => _cancelMemo.runOnce(() { |
+ if (_fired) return null; |
+ _isCanceled = true; |
+ if (_onCancel != null) return _onCancel(); |
+ }); |
+ final _cancelMemo = new AsyncMemoizer(); |
Lasse Reichstein Nielsen
2015/08/27 10:20:54
Move field to top of class.
nweiz
2015/08/28 00:34:56
I will if you insist, but I think it's a lot clear
Lasse Reichstein Nielsen
2015/09/03 13:06:17
I still prefer to have all the fields collected in
nweiz
2015/09/08 21:14:45
Done.
|
+} |