com.hp.util.dcord.peer

Interface PeerMonitor<P>

Type Parameters:

P - type of the peer's status

All Superinterfaces:

Observable<PeerListener<P>>

All Known Implementing Classes:

PubSubPeerMonitor

public interface PeerMonitor<P>
extends Observable<PeerListener<P>>

Peer monitor used to track the status of peers.

Peer monitor allows peers to get status from each other. Sometimes defining a status for the entire node does not work because by the time the node is recognized as active, some services may not be. As an example imagine a component based application where components are initialized following a particular order. Some components may not be ready by the time the node is recognized as reachable (either active or inactive). Using a PeerMonitor components will get notifications of their peers, which are the ones they interact with in a distributed system.

One example would be the usage of PublishSubscribeService. Using PeerMonitor components would make sure when the peers are ready to receive messages (They have subscribed).

Intuitive idea:

 --------------------------------                            --------------------------------
 |             ...              |                            |             ...              | 
 |  --------------------------  |                            |  --------------------------  | 
 |  |        Layer k+1       |  |  <-- Peer Monitor K+1 -->  |  |        Layer k+1       |  | 
 |  --------------------------  |                            |  --------------------------  | 
 |  --------------------------  |                            |  --------------------------  | 
 |  |        Layer k         |  |  <--  Peer Monitor K  -->  |  |        Layer k         |  | 
 |  --------------------------  |                            |  --------------------------  | 
 |             ...              |                            |             ...              | 
 --------------------------------                            --------------------------------
             Node i                                                      Node j
 

Note that layer could be a component, service, application, etc. Any distributed algorithm that coordinates with its peers.

Author:

Fabiel Zuniga

Method Summary

Methods

Modifier and Type	Method and Description
Collection<Pair<Node,P>>	getKnownPeers() Gets known peers (including the local peer if its initial state has been reported via updateLocalPeer(Object)) which are the peers for which the state is considered up to date.
Collection<Pair<Node,P>>	getUnknownPeers() Gets unknown peers (including the local peer if its initial state has not been reported via updateLocalPeer(Object)) which are the peers for which the state is considered unknown or out of date: These are peers that have never joined the cluster, peers that have not reported status after they left, or peers that previously reported status but the node they belong to are not part of ClusterService.getActiveNodes().
void	updateLocalPeer(P localPeer) Updates the state of the local peer.

Methods inherited from interface com.hp.util.observer.Observable

register, unregister

Method Detail

updateLocalPeer

void updateLocalPeer(P localPeer)

Updates the state of the local peer.

This method should be called when the initial state of the local peer is available, and after that when such state changes.

Parameters:

localPeer - local peer

getKnownPeers

Collection<Pair<Node,P>> getKnownPeers()

Gets known peers (including the local peer if its initial state has been reported via updateLocalPeer(Object)) which are the peers for which the state is considered up to date. These are peers that have reported status and for which the node they belong to are part of ClusterService.getActiveNodes(). Note that a peer is only known if it has reported status after joining the cluster; Thus, a node that is part of ClusterService.getActiveNodes() is not guaranteed to be known.

Returns:

reachable peers.

getUnknownPeers

Collection<Pair<Node,P>> getUnknownPeers()

Gets unknown peers (including the local peer if its initial state has not been reported via updateLocalPeer(Object)) which are the peers for which the state is considered unknown or out of date: These are peers that have never joined the cluster, peers that have not reported status after they left, or peers that previously reported status but the node they belong to are not part of ClusterService.getActiveNodes().

The peer's status included in the result is the last known if available, otherwise null.

Returns:

unreachable peers.