interface ISimpleBlockingGuard
{
  in void ia();

  behaviour
  {
    on ia: {}
  }
}

component SimpleBlockingGuard
{
  provides ISimpleBlockingGuard pp;

  behaviour
  {
    bool deadlock = false;
    on pp.ia(): blocking
      {
        [deadlock] {}
        [otherwise] {pp.reply(); deadlock = true;}
      }
  }
}