def notifications(self):
        """
        Generator method that yields all HMC notifications (= JMS messages)
        received by this notification receiver.

        Example::

            receiver = zhmcclient.NotificationReceiver(topic, hmc, userid,
                                                       password)
            for headers, message in receiver.notifications():
                . . .

        Yields:

          : A tuple (headers, message) representing one HMC notification, with:

          * headers (dict): The notification header fields.

            Some important header fields (dict items) are:

            * 'notification-type' (string): The HMC notification type (e.g.
              'os-message', 'job-completion', or others).

            * 'session-sequence-nr' (string): The sequence number of this HMC
              notification within the session created by this notification
              receiver object. This number starts at 0 when this receiver
              object is created, and is incremented each time an HMC
              notification is published to this receiver.

            * 'class' (string): The class name of the HMC resource publishing
              the HMC notification (e.g. 'partition').

            * 'object-id' (string) or 'element-id' (string): The ID of the HMC
              resource publishing the HMC notification.

            For a complete list of notification header fields, see section
            "Message format" in chapter 4. "Asynchronous notification" in the
            :term:`HMC API` book.

          * message (:term:`JSON object`): Body of the HMC notification,
            converted into a JSON object.

            The properties of the JSON object vary by notification type.

            For a description of the JSON properties, see the sub-sections
            for each notification type within section "Notification message
            formats" in chapter 4. "Asynchronous notification" in the
            :term:`HMC API` book.
        """

        while True:
            with self._handover_cond:

                # Wait until MessageListener has a new notification
                while len(self._handover_dict) == 0:
                    self._handover_cond.wait(self._wait_timeout)

                if self._handover_dict['headers'] is None:
                    return

                # Process the notification
                yield (self._handover_dict['headers'],
                       self._handover_dict['message'])

                # Indicate to MessageListener that we are ready for next
                # notification
                del self._handover_dict['headers']
                del self._handover_dict['message']
                self._handover_cond.notifyAll()
Generator method that yields all HMC notifications (= JMS messages)
        received by this notification receiver.

        Example::

            receiver = zhmcclient.NotificationReceiver(topic, hmc, userid,
                                                       password)
            for headers, message in receiver.notifications():
                . . .

        Yields:

          : A tuple (headers, message) representing one HMC notification, with:

          * headers (dict): The notification header fields.

            Some important header fields (dict items) are:

            * 'notification-type' (string): The HMC notification type (e.g.
              'os-message', 'job-completion', or others).

            * 'session-sequence-nr' (string): The sequence number of this HMC
              notification within the session created by this notification
              receiver object. This number starts at 0 when this receiver
              object is created, and is incremented each time an HMC
              notification is published to this receiver.

            * 'class' (string): The class name of the HMC resource publishing
              the HMC notification (e.g. 'partition').

            * 'object-id' (string) or 'element-id' (string): The ID of the HMC
              resource publishing the HMC notification.

            For a complete list of notification header fields, see section
            "Message format" in chapter 4. "Asynchronous notification" in the
            :term:`HMC API` book.

          * message (:term:`JSON object`): Body of the HMC notification,
            converted into a JSON object.

            The properties of the JSON object vary by notification type.

            For a description of the JSON properties, see the sub-sections
            for each notification type within section "Notification message
            formats" in chapter 4. "Asynchronous notification" in the
            :term:`HMC API` book.