Simple failure detection protocol. Periodically sends a are-you-alive message to a randomly chosen member
(excluding itself) and waits for a response. If a response has not been received within timeout msecs, a counter
associated with that member will be incremented. If the counter exceeds max_missed_hbs, that member will be
suspected. When a message or a heartbeat are received, the counter is reset to 0.
This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket).
Will be called from top to bottom. This means that at the time of the method invocation the
neighbor protocol below is still working. This method will replace the
STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that
when this method is called all messages in the down queue will have been flushed
An event was received from the layer below. Usually the current layer will want to examine
the event type and - depending on its type - perform some computation
(e.g. removing headers from a MSG event type, or updating the internal membership list
when receiving a VIEW_CHANGE event).
Finally the event is either a) discarded, or b) an event is sent down
the stack using down_prot.down() or c) the event (or another event) is sent up
the stack using up_prot.up().
An event is to be sent down the stack. The layer may want to examine its type and perform
some action on it, depending on the event's type. If the event is a message MSG, then
the layer may need to add a header to it (or do nothing at all) before sending it down
the stack using down_prot.down(). In case of a GET_ADDRESS event (which tries to
retrieve the stack's address from one of the bottom layers), the layer may need to send
a new response event back up the stack using up_prot.up().