[hibernate-dev] HHH-9993 - IsolationDelegate + no-Connection

HHH-9993[1] is a request to extend IsolationDelegate to cater for transaction hooks which do not need access to a JDBC Connection. A quick primer for those unfamiliar, IsolationDelegate is a contract to allow work to be done in a fashion that makes sure it is isolated from the main Session transaction. We have implementations of this to fit JTA and JDBC scenarios. Additionally, it allows to indicate that the isolated work should itself be transacted or not. In the JDBC-transaction scenario (which HHH-9993 deals with) transacted-isolated work is achieved by passing in a separate Connection to use since that is the only way to achieve a new transaction in JDBC (JDBC has no "suspend/resume" transaction functionality). HHH-9993 is again about this isolated, transacted scenario under the JDBC-transaction handling. Specifically for hibernate-infinispan call backs there is no need to obtain the second Connection. So HHH-9993 is about reducing the overhead of this call by allowing it a way to say "I need to do some isolated, transacted work but I do not need the Connection". For this particular use case that is fine: hibernate-infinispan will never access the Connection. I do worry however about this general use-case. My concern is specifically that some use cases will attempt to call back into the Session. At the moment we do not "protect" against that. I'd like to get some opinions on this. [1] https://hibernate.atlassian.net/browse/HHH-9993