acquire method

Future<void> acquire([ CancelToken? cancelToken ])

Resolves when a slot is available.

Throws CancelledException when cancelToken is (or becomes) cancelled while waiting; an already-admitted caller is unaffected.

Implementation

Future<void> acquire([CancelToken? cancelToken]) {
  cancelToken?.throwIfCancelled();
  if (_current < _max) {
    _current++;
    return Future<void>.value();
  }
  final completer = Completer<void>();
  var settled = false;
  void waiter() {
    if (settled) return;
    settled = true;
    completer.complete();
  }

  _queue.add(waiter);
  if (cancelToken != null) {
    unawaited(
      cancelToken.onCancel.then((_) {
        if (settled) return;
        settled = true;
        _queue.remove(waiter);
        completer.completeError(CancelledException(cancelToken.cancelReason));
        // Nobody may await the future (caller raced away); never crash.
        completer.future.ignore();
      }),
    );
  }
  return completer.future;
}