blob: 432cc22c29d8aaed15518cd6821f3ca3bf7df788 [file] [log] [blame]
// Copyright (c) 2016, 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";
/// A stream that combines the values of other streams.
///
/// This emits lists of collected values from each input stream. The first list
/// contains the first value emitted by each stream, the second contrains the
/// second value, and so on. The lists have the same ordering as the iterable
/// passed to [new StreamZip].
///
/// Any errors from any of the streams are forwarded directly to this stream.
class StreamZip<T> extends Stream<List<T>> {
final Iterable<Stream<T>> _streams;
StreamZip(Iterable<Stream<T>> streams) : _streams = streams;
StreamSubscription<List<T>> listen(void onData(List data), {
Function onError,
void onDone(),
bool cancelOnError}) {
cancelOnError = identical(true, cancelOnError);
List<StreamSubscription> subscriptions = <StreamSubscription>[];
StreamController controller;
List current;
int dataCount = 0;
/// Called for each data from a subscription in [subscriptions].
void handleData(int index, data) {
current[index] = data;
dataCount++;
if (dataCount == subscriptions.length) {
List data = current;
current = new List(subscriptions.length);
dataCount = 0;
for (int i = 0; i < subscriptions.length; i++) {
if (i != index) subscriptions[i].resume();
}
controller.add(data);
} else {
subscriptions[index].pause();
}
}
/// Called for each error from a subscription in [subscriptions].
/// Except if [cancelOnError] is true, in which case the function below
/// is used instead.
void handleError(Object error, StackTrace stackTrace) {
controller.addError(error, stackTrace);
}
/// Called when a subscription has an error and [cancelOnError] is true.
///
/// Prematurely cancels all subscriptions since we know that we won't
/// be needing any more values.
void handleErrorCancel(Object error, StackTrace stackTrace) {
for (int i = 0; i < subscriptions.length; i++) {
subscriptions[i].cancel();
}
controller.addError(error, stackTrace);
}
void handleDone() {
for (int i = 0; i < subscriptions.length; i++) {
subscriptions[i].cancel();
}
controller.close();
}
try {
for (Stream stream in _streams) {
int index = subscriptions.length;
subscriptions.add(stream.listen(
(data) { handleData(index, data); },
onError: cancelOnError ? handleError : handleErrorCancel,
onDone: handleDone,
cancelOnError: cancelOnError));
}
} catch (e) {
for (int i = subscriptions.length - 1; i >= 0; i--) {
subscriptions[i].cancel();
}
rethrow;
}
current = new List(subscriptions.length);
controller = new StreamController<List>(
onPause: () {
for (int i = 0; i < subscriptions.length; i++) {
// This may pause some subscriptions more than once.
// These will not be resumed by onResume below, but must wait for the
// next round.
subscriptions[i].pause();
}
},
onResume: () {
for (int i = 0; i < subscriptions.length; i++) {
subscriptions[i].resume();
}
},
onCancel: () {
for (int i = 0; i < subscriptions.length; i++) {
// Canceling more than once is safe.
subscriptions[i].cancel();
}
}
);
if (subscriptions.isEmpty) {
controller.close();
}
return controller.stream.listen(onData,
onError: onError,
onDone: onDone,
cancelOnError: cancelOnError);
}
}