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• SPChangeRefusedMessage - from a Leader to a Member when, by the time the change would be processed, it is no longer applicable.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

Nested Class Summary

private class	SinglePhaseDisseminator.ConnectionChangeQueue Private inner class to maintain a queue of connection changes to be processed.
private class	SinglePhaseDisseminator.DebugFrame ## For testing.
private class	SinglePhaseDisseminator.MessageListener A private inner class to listen for group changes (non-leaders) or notification messages (leaders).
private class	SinglePhaseDisseminator.ProcessMessageQueue Queue so that we can pause processing of messages during disengagement.

Field Summary

private SinglePhaseDisseminator.ConnectionChangeQueue	connectionChangeQueue Leader-only.
private java.util.Hashtable	connections Leader-only.
private SinglePhaseDisseminator.DebugFrame	debugFrame For debugging.
private boolean	debugging Determines whether to output log messages and show debugFrame.
private java.lang.Boolean	disengaging If I am currently disengaging, is set to true.
private int	disseminatorPort The port to send/receive messages on.
private Member	engaging If I am currently engaging, contains the Member with which I'm engaging.
private SPGroupChangeMessage	lastGroupChangeMessage Keep track of the last GroupChangeMessage we've received in order to make sure new ones are in fact newer.
private Member	leader Reference to the leader of the group.
private SinglePhaseDisseminator.MessageListener	messageListener Listens for messages from fellow group members.
private int	portOffset The offset to use to find the port that the disseminators should communicate on (relative to the groupmgmt port passed to GroupManager).
private SinglePhaseDisseminator.ProcessMessageQueue	processMessageQueue Queues received messages for processing.

Fields inherited from class groupmgmt.GroupDisseminator

Constructor Summary

SinglePhaseDisseminator(int portOffset)
Constructor.

Method Summary

private void	addConnection(Member m1, Member m2) Private utility method to add a connection to my network graph.
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.
private void	getGroupOfMember(Member m, java.util.Vector g, java.util.Hashtable table, java.util.Hashtable newTable) Leader-only.
private boolean	isLeader() Accessor to isLeader variable.
private void	log(java.lang.String msg) For testing.
private java.util.Vector	partitionGroups() Leader-only.
private void	processArriving(SPChange arrive) Leader-only.
private void	processChangeRefusedMessage(SPChangeRefusedMessage message) The connection change we sent to a leader has been refused because it no longer applies to that leader.
private void	processConnectionChangesMessage(SPConnectionChangesMessage m) Leader-only.
private void	processDeparting(java.util.Vector departing) Leader-only.
private void	processGetLeaderMessage(SPGetLeaderMessage message) Sent by the leader of another group that wishes to add me.
private void	processGroupChangeMessage(SPGroupChangeMessage message) Process a change in the group (split or new members) sent out by the leader.
private void	processGroupInfoMessage(SPGroupInfoMessage message) Leader-only.
private void	processLeaderAddressMessage(SPLeaderAddressMessage message) Leader-only.
private void	processMessage(java.lang.Object message) Process a Message received by the MessageListener.
private void	sendMessage(Member receiver, java.io.Serializable message) Utility method to send a message to a Member.
private void	sendMessage(java.util.Vector receivers, java.io.Serializable message)
private void	sendOutGroup(java.util.Hashtable gconns, Member gleader, java.util.Vector gmembers) Utility method to send GroupChangeMessages creating a new group.
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

Field Detail

disseminatorPort

private int disseminatorPort

The port to send/receive messages on. Set by adding portOffset to the port passed to GroupManager. Note that if the port is in use, we exit.

portOffset

private int portOffset

The offset to use to find the port that the disseminators should communicate on (relative to the groupmgmt port passed to GroupManager).

messageListener

private SinglePhaseDisseminator.MessageListener messageListener

Listens for messages from fellow group members.

connectionChangeQueue

private SinglePhaseDisseminator.ConnectionChangeQueue connectionChangeQueue

Leader-only. Queues ConnectionChanges to be processed.

processMessageQueue

private SinglePhaseDisseminator.ProcessMessageQueue processMessageQueue

Queues received messages for processing.

leader

private Member leader

Reference to the leader of the group.

connections

private java.util.Hashtable connections

Leader-only. A Hashtable, keyed by Member, with each element being a Vector of other Members that the Member has a connection to. Connections are not assumed or guaranteed to be symmetric here, but they should end up being symmetric.

engaging

private Member engaging

If I am currently engaging, contains the Member with which I'm engaging. For synchronization purposes - allows us to block while engaging with a Member.

disengaging

private java.lang.Boolean disengaging

If I am currently disengaging, is set to true. For synchronization purposes - allows us to block while splitting the group.

lastGroupChangeMessage

private SPGroupChangeMessage lastGroupChangeMessage

Keep track of the last GroupChangeMessage we've received in order to make sure new ones are in fact newer.

debugFrame

private SinglePhaseDisseminator.DebugFrame debugFrame

For debugging.

debugging

private boolean debugging

Determines whether to output log messages and show debugFrame.

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)

Specified by:

start in class GroupDisseminator

stop

protected void stop()

Suspend all activity - stop responding to changeGroup events.

Specified by:

stop in class GroupDisseminator

isLeader

private boolean isLeader()

Accessor to isLeader variable.

Returns:

True if I'm the group leader, false otherwise.

changeGroup

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

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

Specified by:

changeGroup in class GroupDisseminator

Parameters:

arriving - The new Member(s).

departing - The leaving Member(s).

processConnectionChangesMessage

private void processConnectionChangesMessage(SPConnectionChangesMessage m)

Leader-only. Update the connections Hashtable to reflect changes in Member connectivity. If there are new Member(s) or any old Member(s) have been disconnected from the group, then do a group change.

processChangeRefusedMessage

private void processChangeRefusedMessage(SPChangeRefusedMessage message)

The connection change we sent to a leader has been refused because it no longer applies to that leader. Stick it in the queue again to be sent to the new leader (could be myself).

processArriving

private void processArriving(SPChange arrive)

Leader-only. Add a new Member. First step is to ask the new member for it's leader's address. They will send back a LeaderAddressMessage and then if that leader should lead the new group we'll send a GroupInfoMessage. If we should lead the new group we wait and assume they will send us a GetLeaderMessage, to which we will reply with a LeaderAddressMessage, and they'll reply with a GroupInfoMessage. Then we'll lead the new group.

Parameters:

arrive - The connection to add.

processDeparting

private void processDeparting(java.util.Vector departing)

Leader-only. Changes the connections table to reflect newly dropped connections. Then checks to see if group needs to be split, and if so sends out GroupChangeMessages.

Parameters:

departing - A Vector containing SPChange objects for all of the dropped connections to process. This method removes the SPChange objects that it processes from departing.

partitionGroups

private java.util.Vector partitionGroups()

Leader-only. Helper method for processDeparting() to determine who's connected to whom, and who should lead the new group(s).

Returns:

Vector of groups. Each group is a vector, with its connections as the first element, its leader as the second, and then the rest of the Members.

getGroupOfMember

private void getGroupOfMember(Member m,
                              java.util.Vector g,
                              java.util.Hashtable table,
                              java.util.Hashtable newTable)

Leader-only. Recursive helper method for partitionGroups() to construct a group and connections table from everyone connected to Member m. Removes connections for this group from the initial connections table.

Parameters:

m - The Member to start the new group with.

g - The group.

table - The initial connections hashtable.

newTable - Hashtable to fill with the connections for this group.

processLeaderAddressMessage

private void processLeaderAddressMessage(SPLeaderAddressMessage message)

Leader-only. We got the newMember's Leader's address, now check if it's higher than my address, and if so send a GroupInfoMessage. Otherwise we wait for a GroupInfoMessage from the other leader. This works because connections are assumed to be symmetric.

processGroupInfoMessage

private void processGroupInfoMessage(SPGroupInfoMessage message)

Leader-only. Process a GroupInfoMessage from another leader. Merge it's connections with mine and then send GroupChangeMessages to everyone indicating the new, merged group. (I remain leader).

processGetLeaderMessage

private void processGetLeaderMessage(SPGetLeaderMessage message)

Sent by the leader of another group that wishes to add me. Respond by telling them my leader's address.

processGroupChangeMessage

private void processGroupChangeMessage(SPGroupChangeMessage message)

Process a change in the group (split or new members) sent out by the leader. Tells all about my new group - the leader, the members, and if I'm the leader it tells me the connections too.

Parameters:

message - The GroupChangeMessage.

addConnection

private void addConnection(Member m1,
                           Member m2)

Private utility method to add a connection to my network graph. Connections are symmetric.

Parameters:

m1 - A Member.

m2 - The Member connected to m1.

sendOutGroup

private void sendOutGroup(java.util.Hashtable gconns,
                          Member gleader,
                          java.util.Vector gmembers)

Utility method to send GroupChangeMessages creating a new group.

Parameters:

gconns - The connections table for the new group.

gleader - The leader of the new group.

gmembers - The members of the new group (including the leader).

sendMessage

private void sendMessage(Member receiver,
                         java.io.Serializable message)

Utility method to send a message to a Member.

Parameters:

receiver - The Member to send the message to.

message - The message to send.

sendMessage

private void sendMessage(java.util.Vector receivers,
                         java.io.Serializable message)

processMessage

private void processMessage(java.lang.Object message)

Process a Message received by the MessageListener.

Parameters:

message - The Message to process.

fireGroupChangedEvent

protected void fireGroupChangedEvent(java.util.Vector members)

Helper method to automatically construct the event before firing.

log

private void log(java.lang.String msg)

For testing. Output a message to the command line.