groupmgmt.impl
Class SinglePhaseDisseminator

java.lang.Object
  |
  +--groupmgmt.GroupDisseminator
        |
        +--groupmgmt.impl.SinglePhaseDisseminator

public class SinglePhaseDisseminator

extends GroupDisseminator

The SinglePhaseDisseminator class. Responsible for coordinating group changes with members of the group.

This implementation does that via a "Single-phase transaction", ie it sends a message to everyone in the group and assumes that they got it. One member of the group is designated Leader, and it keeps a graph of the connections within its group (implemented as a Hashtable). The followers notify the leader of changes in their connections, and the leader updates its graph and changes the group when needed.

Multiple removes can be done simultaneously by the leader.
Adds must be serialized (to keep leader-leader communication simple), this is done by the ConnectionChangeQueue.

Messages used:

• SPConnectionChangesMessage - from any Member to leader when its changeGroup method is called by its Detector.
• SPChangeRefusedMessage - from a Leader to a Member when, by the time the change would be processed, it is no longer applicable.
• SPGetLeaderMessage - from a Leader to a newly-connected Member to ask for that member's leader's IP.
• SPLeaderAddressMessage - response to GetLeaderMessage.
• SPGroupInfoMessage - after getting another Leader's address, if it is higher than mine, send this with my current connections graph.
• SPGroupChangeMessage - from Leader to all of old or new group, when group changes. Contains new Leader address and list of Members; the message to the new Leader also includes the connections graph.

## FUTURE WORK:
##
## anticipate potential problems with refusedchanges.
## (theoretically ConnectionChangeMessages could get out of order).
## handle unexpected loss of connection to leader/robustness in general
## test with large groups. algorithms fast/scalable enough?

Version:

July 2003

Author:

Christine Julien, Tom Elgin

Constructor Summary

SinglePhaseDisseminator(int portOffset)
Constructor.

Method Summary

void	changeGroup(Member[] arriving, Member[] departing) Process a change in connectivity detected by MemberDetector Send it to the connectionChangeQueue to process.
protected void	fireGroupChangedEvent(java.util.Vector members) Helper method to automatically construct the event before firing.
void	setDebug(boolean debugging) Determine whether to output logging messages.
protected void	start() Start responding to changeGroup messages.
protected void	stop() Suspend all activity - stop responding to changeGroup events.

Methods inherited from class groupmgmt.GroupDisseminator

addGroupChangedListener, fireGroupChangedEvent, isActive, removeGroupChangedListener

Methods inherited from class java.lang.Object

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

Constructor Detail

SinglePhaseDisseminator

public SinglePhaseDisseminator(int portOffset)

Constructor. Sets port offset and calls super().

Parameters:

portOffset - The offset (relative to the groupmgmt port) to use when communicating with another member's disseminator.

Method Detail

setDebug

public void setDebug(boolean debugging)

Determine whether to output logging messages.

Parameters:

debugging - Outputs messages if true.

start

protected void start()

Start responding to changeGroup messages. (May also start listening for network messages from members)

Overrides:

start in class GroupDisseminator

stop

protected void stop()

Suspend all activity - stop responding to changeGroup events.

Overrides:

stop in class GroupDisseminator

changeGroup

public void changeGroup(Member[] arriving,
                        Member[] departing)

Process a change in connectivity detected by MemberDetector Send it to the connectionChangeQueue to process.

Overrides:

changeGroup in class GroupDisseminator

Parameters:

arriving - The new Member(s).

departing - The leaving Member(s).

fireGroupChangedEvent

protected void fireGroupChangedEvent(java.util.Vector members)

Helper method to automatically construct the event before firing.