This class implements the OracleCloseCallback interface that
is defined in oracle.jdbc.driver. It is used to close a physical
connection to an RM instance, and unregister this RM instance
from C-XA's current thread of control. An instance of this class
should be registered with an OracleXAConnection/OraclePooledConnection,
using the registerCloseCallback() method in the OraclePooledConnection
class to function, like:
((OracleXAConnection) xaconn).registerCloseCallback(
new OracleXAHeteroCloseCallback(), new SomeUserObject());