add method
Wait for task
to complete.
Implementation
@override
void add(Future<T> task) {
if (_closed) throw StateError('The FutureGroup is closed.');
// Ensure that future values are put into [values] in the same order they're
// added to the group by pre-allocating a slot for them and recording its
// index.
var index = _values.length;
_values.add(null);
_pending++;
task.then((value) {
if (_completer.isCompleted) return null;
_pending--;
_values[index] = value;
if (_pending != 0) return null;
var onIdleController = _onIdleController;
if (onIdleController != null) onIdleController.add(null);
if (!_closed) return null;
if (onIdleController != null) onIdleController.close();
_completer.complete(_values.whereType<T>().toList());
}).catchError((Object error, StackTrace stackTrace) {
if (_completer.isCompleted) return null;
_completer.completeError(error, stackTrace);
});
}