co<T> function

Future<T> co<T>(dynamic key, FutureOr<T> action())

used to invoke async functions in order

Implementation

Future<T> co<T>(key, FutureOr<T> action()) async {
  for (;;) {
    final c = _locks[key];
    if (c == null) break;
    try {
      await c.future;
    } catch (_) {} //ignore error (so it will continue)
  }

  final c = _locks[key] = new Completer<T>();
  void then(T result) {
    final c2 = _locks.remove(key);
    c.complete(result);

    assert(identical(c, c2));
  }

  void catchError(ex, StackTrace st) {
    final c2 = _locks.remove(key);
    c.completeError(ex, st);

    assert(identical(c, c2));
  }

  try {
    final result = action();
    if (result is Future<T>) {
      result.then(then).catchError(catchError);
    } else {
      then(result);
    }
  } catch (ex, st) {
    catchError(ex, st);
  }

  return c.future;
}