Investigate statement close behaviour after connection close

[mrotteveel]

Some spurious test failures in the hibernate-orm tests suggests that attempts to close a statement after the connection has been closed may result in error "The connection is closed [SQLState:08006, ISC error code:337248336]"; technically that is valid, but it does suggest that a connection close doesn't always close the associated statements.

This may be some exceptional circumstance, but verify this to be sure.

[mrotteveel]

When the FBManagedConnection, and by extension the FbDatabase is closed (using forceClose()) due to a fatal/broken connection error, none of the listeners close statements (neither java.sql.Statement nor FbStatement), so when the statement is then closed, it tries to write a free statement message, but receives a SQLException because the connection is closed.

A stop gap measure would be for FBStatement.close() to ignore the connection closed exception, but theoretically that would violate JDBC expectations that a SQLException is thrown "if a database access error occurs".

Either FBManagedConnection needs to ensure that FBConnection marks its statements as closed, or listeners on FbDatabase should ensure FbStatement instances (and by extension java.sql.Statement instances) are closed, or both.