org.jgroups.protocols
Class PING
The PING protocol layer retrieves the initial membership (used by the GMS when started
by sending event FIND_INITIAL_MBRS down the stack). We do this by mcasting PING
requests to an IP MCAST address (or, if gossiping is enabled, by contacting the GossipServer).
The responses should allow us to determine the coordinator whom we have to
contact, e.g. in case we want to join the group. When we are a server (after having
received the BECOME_SERVER event), we'll respond to PING requests with a PING
response.
The FIND_INITIAL_MBRS event will eventually be answered with a
FIND_INITIAL_MBRS_OK event up the stack.
The following properties are available
property: timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs
property: num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2
property: gossip_host - if you are using GOSSIP then this defines the host of the GossipServer, default is null
property: gossip_port - if you are using GOSSIP then this defines the port of the GossipServer, default is null
down_handler , down_prot , down_queue , down_thread , down_thread_prio , log , observer , props , stack , up_handler , up_prot , up_queue , up_thread , up_thread_prio |
destroy , down , getDownProtocol , getDownQueue , getName , getProperties , getUpProtocol , getUpQueue , handleSpecialDownEvent , init , passDown , passUp , providedDownServices , providedUpServices , receiveDownEvent , receiveUpEvent , requiredDownServices , requiredUpServices , setDownProtocol , setObserver , setProperties , setPropertiesInternal , setProtocolStack , setUpProtocol , start , startDownHandler , startUpHandler , stop , stopInternal , up |
down
public void down(Event evt)
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 PassDown
. 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 PassUp
.
The PING protocol is interested in several different down events,
Event.FIND_INITIAL_MBRS - sent by the GMS layer and expecting a GET_MBRS_OK
Event.TMP_VIEW and Event.VIEW_CHANGE - a view change event
Event.BECOME_SERVER - called after client has joined and is fully working group member
Event.CONNECT, Event.DISCONNECT.
- down in interface Protocol
setProperties
public boolean setProperties(Properties props)
sets the properties of the PING protocol.
The following properties are available
property: timeout - the timeout (ms) to wait for the initial members, default is 3000=3 secs
property: num_initial_members - the minimum number of initial members for a FIND_INITAL_MBRS, default is 2
property: gossip_host - if you are using GOSSIP then this defines the host of the GossipServer, default is null
property: gossip_port - if you are using GOSSIP then this defines the port of the GossipServer, default is null
- setProperties in interface Protocol
props
- - a property set containing only PING properties
- returns true if all properties were parsed properly
returns false if there are unrecnogized properties in the property set
up
public void up(Event evt)
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
PassDown
or c) the event (or another event) is sent up
the stack using
PassUp
.
For the PING protocol, the Up operation does the following things.
1. If the event is a Event.MSG then PING will inspect the message header.
If the header is null, PING simply passes up the event
If the header is PingHeader.GET_MBRS_REQ then the PING protocol
will PassDown a PingRequest message
If the header is PingHeader.GET_MBRS_RSP we will add the message to the initial members
vector and wake up any waiting threads.
2. If the event is Event.SET_LOCAL_ADDR we will simple set the local address of this protocol
3. For all other messages we simple pass it up to the protocol above
- up in interface Protocol
evt
- - the event that has been sent from the layer below
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