Please, see UNDERTOW-1758.
There is the chance of race condition in state fields, and this needs to be handled just like done in https://github.com/xnio/xnio/blob/3.x/api/src/main/java/org/xnio/Connection.java

The most common scenario is a state is changed by a close request or an error handling code while the state is also being edited by another thread, tipically the one that is handling or sending a request.

To implement this Jira, careful consideration is needed for each state field in Undertow, to verify if that field can be edited by more than a single thread or not.