class SSLTransport(...):

    def __nss_initialized(...):
        """
        If there is another connections open it may have already
        initialized NSS. This is likely to lead to an NSS shutdown
        failure.  One way to mitigate this is to tell NSS to not
        initialize if it has already been done in another open connection.

        Returns True if another connection is using the same db.
        """
        for value in context.__dict__.values():
            ...
            # check if the connection is using the same db
            if hasattr(value.conn._ServerProxy__transport, 'dbdir') and \
              value.conn._ServerProxy__transport.dbdir == dbdir:
                return True
        return False

    def make_connection(...):
        ...
        # If we an existing connection exists using the same NSS database
        # there is no need to re-initialize. Pass this into the NSS
        # connection creator.
        ....

        # if there is already a connection using the same db,
        # don't initialize the db again
        no_init = self.__nss_initialized(dbdir)
            ...
            conn = NSSConnection(host, 443, dbdir=dbdir, no_init=no_init)

        ...

class NSSConnection(...):

    def __init__(...):
        """
        ...
        :param no_init: do not initialize the NSS database. This requires
                        that the database has already been initialized or
                        the request will fail.
        """
        ...

        if not no_init and nss.nss_is_initialized():
            # close any open NSS database and use the new one
            ...
                nss.nss_shutdown()

        nss.nss_init(dbdir)
        ...

class vault_retrieve(...):

    def forward(...):

        ... initialize db ...

        session_key = ... generate session key ...
        nss_transport_cert = ... get transport cert from db ...
        wrapped_session_key = ... encrypt session key with transport cet ...

        ...

        # get encrypted data from server which will
        # use NSSConnection (which will shutdown the current db)
        response = super(vault_retrieve, self).forward(...)

        secret = ... decrypt data using the same session key ...