Language/Statements/Yield_and_Yield_Each/Yield/execution_async_t04.dart

// 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.

/// @assertion Execution of a statement s of the form yield e; proceeds as
/// follows:
///    First, the expression e is evaluated to an object o. If the enclosing
///  function m is marked async* and the stream u associated with m has been
///  paused, then execution of m is suspended until u is resumed or canceled.
///    Next, o is added to the iterable or stream associated with the immediately
///  enclosing function.
///    If the enclosing function m is marked async* and the stream u associated
///  with m has been canceled, then let c be the finally clause (17.11) of the
///  innermost enclosing try-finally statement, if any. If c is defined, let h be
///  the handler induced by c. If h is defined, control is transferred to h. If
///  h is undefined, the immediately enclosing function terminates.
///    The stream associated with an asynchronous generator could be canceled by
///  any code with a reference to that stream at any point where the generator
///  was passivated. Such a cancellation constitutes an irretrievable error for
///  the generator. At this point, the only plausible action for the generator
///  is to clean up after itself via its finally clauses.
///    Otherwise, if the enclosing function m is marked async* (9) then the
///  enclosing function may suspend.
///
/// @description Check that the immediately enclosing function terminates, if
/// the stream u associated with m has been canceled and there is no 'finally'
/// handler defined.
///
/// @author a.semenov@unipro.ru

import 'dart:async';
import '../../../../Utils/expect.dart';

bool generatorAlive = false;

Stream<int> generator() async* {
  int i = 0;
  while (true) {
    generatorAlive = true;
    yield i++;
  }
}

test() async {
  generatorAlive = false;
  Stream<int> s = generator();
  late StreamSubscription<int> ss;
  ss = s.listen(
      (int x) async {
        if (x == 5) { // let generator to work some time
          Expect.equals(true, generatorAlive);
          await ss.cancel();
          generatorAlive = false;
          // verify that generator is not active
          for (int i = 0; i < 10; i++) {
            Expect.equals(false, generatorAlive);
            await new Future.delayed(new Duration(milliseconds: 10));
          }
          asyncEnd();
        }
      }
  );
}

main() {
  asyncStart();
  test();
}