private void checkUnreadyConnectionsStatus() {
    Iterator<String> iterator = unreadyConnections.iterator();
    while (iterator.hasNext()) {
      String connId = iterator.next();
      if (isChannelReady(connId)) {
        connected.add(connId);
        iterator.remove();
        metrics.selectorConnectionCreated.inc();
      }
    }
  }
Check readiness for unready connections and add to completed list if ready
ambry-network/src/main/java/com/github/ambry/network/Selector.java