public void returnConnection(Connection connection) {
    int inFlight = connection.inFlight.decrementAndGet();

    if (connection.isDefunct()) {
      if (host.getMonitor().signalConnectionFailure(connection.lastException())) shutdown();
      else replace(connection);
    } else {

      if (trash.contains(connection) && inFlight == 0) {
        if (trash.remove(connection)) close(connection);
        return;
      }

      if (connections.size() > options().getCoreConnectionsPerHost(hostDistance)
          && inFlight <= options().getMinSimultaneousRequestsPerConnectionThreshold(hostDistance)) {
        trashConnection(connection);
      } else {
        signalAvailableConnection();
      }
    }
  }