code: private void maybeShutdownNowSubchannels() {
      if (shutdownNowed) {
        for (InternalSubchannel subchannel : subchannels) {
          subchannel.shutdownNow(SHUTDOWN_NOW_STATUS);
        }
        for (OobChannel oobChannel : oobChannels) {
          oobChannel.getInternalSubchannel().shutdownNow(SHUTDOWN_NOW_STATUS);
        }
      }
    }
docs: Must be called from syncContext