net.jini.discovery

Class AbstractLookupDiscoveryManager.GroupDiscoveryListener

java.lang.Object

net.jini.discovery.AbstractLookupDiscoveryManager.LocatorDiscoveryListener

net.jini.discovery.AbstractLookupDiscoveryManager.GroupDiscoveryListener

All Implemented Interfaces:

EventListener, DiscoveryChangeListener, DiscoveryListener

Enclosing class:

AbstractLookupDiscoveryManager

private final class AbstractLookupDiscoveryManager.GroupDiscoveryListener
extends AbstractLookupDiscoveryManager.LocatorDiscoveryListener
implements DiscoveryChangeListener

Class that defines the listener that is registered with the LookupDiscovery that performs group discovery on behalf of this LookupDiscoveryManager.

Constructor Summary

Constructors

Modifier	Constructor and Description
private	GroupDiscoveryListener()

Method Summary

Modifier and Type	Method and Description
void	changed(DiscoveryEvent e) Called by LookupDiscovery to send a changed event to this listener when that LookupDiscovery has determined that the member groups of a previously discovered registrar (reg) have changed.
void	discarded(DiscoveryEvent e) Called by LookupDiscovery to send a discarded event to this listener when one of the following events occurs affecting at least one registrar (reg) that was previously discovered through either group discovery alone, or through both group and locator discovery: The method LookupDiscovery.discard was called because the reg was determined to be unreachable.
void	discovered(DiscoveryEvent e) Called by LookupDiscovery to send a discovered event to this listener when that LookupDiscovery has discovered at least one registrar (reg) belonging to at least one of the groups desired by this LookupDiscoveryManager.

Methods inherited from class net.jini.discovery.AbstractLookupDiscoveryManager.LocatorDiscoveryListener

removeDiscoveredSet

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GroupDiscoveryListener

private GroupDiscoveryListener()

Method Detail

discovered

public void discovered(DiscoveryEvent e)

Called by LookupDiscovery to send a discovered event to this listener when that LookupDiscovery has discovered at least one registrar (reg) belonging to at least one of the groups desired by this LookupDiscoveryManager. The reg(s) referenced in the given discovered event may, or may not, have also been previously discovered through locator discovery. If this LookupDiscoveryManager has no prior knowledge of a particular reg referenced in the given discovered event when the LookupDiscovery invokes this method, then this method will send to the listeners registered with this LookupDiscoveryManager, a discovered event referencing that reg; otherwise, depending on whether or not the set of member groups referenced in the given discovered event equal the member groups currently associated with the reg from that event, this method may send a changed event, or may simply update state and send no event at all.

Specified by:

discovered in interface DiscoveryListener

Overrides:

discovered in class AbstractLookupDiscoveryManager.LocatorDiscoveryListener

Parameters:

e - the event that describes the discovered registrars

discarded

public void discarded(DiscoveryEvent e)

Called by LookupDiscovery to send a discarded event to this listener when one of the following events occurs affecting at least one registrar (reg) that was previously discovered through either group discovery alone, or through both group and locator discovery:

• The method LookupDiscovery.discard was called because the reg was determined to be unreachable. In this case, the discarded event received from the LookupDiscovery is referred to as an "active communication discard".
• The LookupDiscovery has determined that the reg has stopped sending multicast announcements. In this case, the discarded event received from the LookupDiscovery is referred to as a "passive communication discard".
• Either the method setGroups or the method removeGroups has been called on the LookupDiscovery, and the resulting new set of desired groups no longer intersects the set of member groups of the discarded reg. In this case, the discarded event received from the LookupDiscovery is referred to as an "active no-interest discard".
• The member groups of the discarded reg have been changed in such a way that the set of member groups associated with the discarded reg no longer intersects the set of desired groups to discover. In this case, the discarded event received from LookupDiscovery is referred to as a "passive no-interest discard".

Depending on the type of discarded event received from the LookupDiscovery as described above, and depending on whether the discarded reg was previously discovered by group discovery alone, or by both group and locator discovery, this method will determine whether to send a discarded event, a changed event, or no event at all. Note that because the discarded event was sent by the LookupDiscovery, the discarded reg could not have been previously discovered by locator discovery alone. Note also that even though a discarded event is received by this method, there are conditions in which a changed event is ultimately sent to the listeners registered with this LookupDiscoveryManager (see below). The following describes the logic used by this method to determine whether or not to send an event to the registered listeners of this LookupDiscoveryManager, as well as what type of event to send. Note that this method concludes that the current discarded event must be a communication discard when the the set of desired groups still intersects the discarded reg's current set of member groups. This is because when interest in the reg still exists, LookupDiscovery will discard the reg only when it has determined that the reg is unreachable. Thus, for a particular reg referenced in the given discarded event,

• if the member groups contained in the discarded event from the LookupDiscovery are identical to the previously discovered member groups of that reg, and if if those member groups still intersect the current set of desired groups (still interested in the reg), then this method will conclude that the discarded event must be either an active or a passive communication discard. When the discard is a communication discard (either active or passive), if the reg was previously discovered by only group discovery, this method sends a discarded event. But if the reg was previously discovered by locator discovery as well as group discovery, then rather than sending a discarded event here, LookupLocatorDiscovery.discard is called (through a call to reg.discard), which will send a discarded event to LocatorDiscoveryListener, which then ultimately sends a discarded event to the registered listeners of this LookupDiscoveryManager.
• if the member groups contained in the discarded event from the LookupDiscovery are identical to the previously discovered member groups of that reg, but those member groups NO LONGER intersect the current set of desired groups, then this method will conclude that the discarded event must be an active no-interest discard. When the discard is an active no-interest discard, if the discarded reg was previously discovered by ONLY group discovery, then a discarded event is sent; otherwise, no event is sent (see section DU.2.4.1 of the "Jini Discovery Utilities Specification").
• if the member groups contained in the discarded event from the LookupDiscovery neither intersect the current set of desired groups (indicating no interest), nor are they identical to the previously discovered member groups of that reg (the member groups have changed), this method will conclude that the discarded event must be a passive no-interest discard. When the discard is a passive no-interest discard, if the discarded reg was previously discovered by locator discovery as well as group discovery, a changed event is is sent to the appropriate listeners; otherwise a discarded event is sent. A changed event is sent when the reg was previously discovered by both group and locator discovery because the fact that the reg was discovered via locator discovery indicates continued interest in the reg, even though the reg was discarded with respect to group discovery. In this case, since the member groups have actually changed (changed in such a way that the LookupDiscovery sent a discarded event), and since there is still interest in that reg, it is more appropriate to send a changed event here rather than a discarded event.

The logic described above can be collapsed into the following decision process:

      if(discovered by group discovery alone) {
          send discarded event
      } else {//discovered by both group and locator discovery
          if(NO LONGER interested in member groups) {
              if(member group have changed) {
                  send changed event
              }
          } else {//still interested in member groups
              call discard on LookupLocatorDiscovery
          }
      }
  

Specified by:

discarded in interface DiscoveryListener

Overrides:

discarded in class AbstractLookupDiscoveryManager.LocatorDiscoveryListener

Parameters:

e - the event that describes the discarded registrars

changed

public void changed(DiscoveryEvent e)

Called by LookupDiscovery to send a changed event to this listener when that LookupDiscovery has determined that the member groups of a previously discovered registrar (reg) have changed. This method extracts and records the appropriate information from the given changed event, and then sends a changed event to the appropriate listeners registered with this LookupDiscoveryManager.

Specified by:

changed in interface DiscoveryChangeListener

Parameters:

e - instance of net.jini.discovery.DiscoveryEvent representing the event that describes the lookup services whose discovery state has changed