The ActiveMQ JCA layer may leak threads of name "ActiveMQ Connection Executor" and instances of org.apache.activemq.ActiveMQConnection when there are problems with establishing the connection.
If the initial openwire connection cannot be established, it may run an "ActiveMQ Connection Executor" thread to deal with the error leading to a code path that does not close the connection and does not clear up the "ActiveMQ Connection Executor" thread.
Low level details in further comments.

This problem can be reproduced by running ActiveMQResourceAdapter.TransactionContext.recover() but potentially other code paths in the resource adapter are effected as well.