org.jgroups
Interface MembershipListener

All Known Subinterfaces:

Receiver

All Known Implementing Classes:

Chat, Draw, PartitionedHashMap, PartitionedHashMap.ConsistentHashFunction, QuoteClient, QuoteServer, ReceiverAdapter, RELAY.Receiver, RelayDemoRpc, Relayer.Bridge, ReplCache, ReplicatedHashMap, ReplicatedTree, ViewDemo, Whiteboard

public interface MembershipListener

Allows a listener to be notified when group membership changes.

The MembershipListener interface is similar to the MessageListener interface: every time a new view, a suspicion message, or a block event is received, the corresponding method of the class implementing MembershipListener will be called. MembershipListener is often used in JGroups building blocks installed on top of a channel i.e RpcDispatcher and MessageDispatcher. Oftentimes the only method containing any functionality will be viewAccepted() which notifies the receiver that a new member has joined the group or that an existing member has left or crashed.

Since:

2.0

Author:

Bela Ban, Vladimir Blagojevic

See Also:

RpcDispatcher

Method Summary

void	block() Called (usually by the FLUSH protocol), as an indication that the member should stop sending messages.
void	suspect(Address suspected_mbr) Called whenever a member is suspected of having crashed, but has not yet been excluded.
void	unblock() Called after the FLUSH protocol has unblocked previously blocked senders, and messages can be sent again.
void	viewAccepted(View new_view) Called when a change in membership has occurred.

Method Detail

viewAccepted

void viewAccepted(View new_view)

Called when a change in membership has occurred. No long running actions, sending of messages or anything that could block should be done in this callback. If some long running action needs to be performed, it should be done in a separate thread.

Note that on reception of the first view (a new member just joined), the channel will not yet be in the connected state. This only happens when Channel.connect(String) returns.

suspect

void suspect(Address suspected_mbr)

Called whenever a member is suspected of having crashed, but has not yet been excluded.

block

void block()

Called (usually by the FLUSH protocol), as an indication that the member should stop sending messages. Any messages sent after returning from this callback might get blocked by the FLUSH protocol. When the FLUSH protocol is done, and messages can be sent again, the FLUSH protocol will simply unblock all pending messages. If a callback for unblocking is desired, implement unblock(). Note that block() is the equivalent of reception of a BlockEvent in the pull mode.

unblock

void unblock()

Called after the FLUSH protocol has unblocked previously blocked senders, and messages can be sent again. This callback only needs to be implemented if we require a notification of that.

Note that during new view installation we provide guarantee that unblock invocation strictly follows view installation at some node A belonging to that view . However, some other message M may squeeze in between view and unblock callbacks. For more details see https://jira.jboss.org/jira/browse/JGRP-986