org.jgroups.blocks

Class VotingAdapter

Implemented Interfaces:
MembershipListener, MessageListener

public class VotingAdapter
extends java.lang.Object
implements MessageListener, MembershipListener

Voting adapter provides a voting functionality for an application. There should be at most one VotingAdapter listening on one Channel instance. Each adapter can have zero or more registered VotingListener instances that will be called during voting process.

Decree is an object that has some semantic meaning within the application. Each voting listener receives a decree and can respond with either true or false. If the decree has no meaning for the voting listener, it is required to throw VotingException. In this case this specific listener will be excluded from the voting on the specified decree. After performing local voting, this voting adapter sends the request back to the originator of the voting process. Originator receives results from each node and decides if all voting process succeeded or not depending on the consensus type specified during voting.

Author:
Roman Rokytskyy (rrokytskyy@acm.org)

Nested Class Summary

static class
VotingAdapter.FailureVoteResult
Class that represents a result of local voting on the failed node.
static class
VotingAdapter.VoteResult
This class represents the result of local voting.

Field Summary

static int
VOTE_ALL
This consensus type means that at least one positive vote and no negative votes are required for the voting to succeed.
static int
VOTE_ANY
This consensus type means that at least one positive vote is required for the voting to succeed.
static int
VOTE_MAJORITY
This consensus type means that number of positive votes should be greater than number of negative votes.
protected Log
log

Constructor Summary

VotingAdapter(Channel channel)
Creates an instance of the VoteChannel that uses JGroups for communication between group members.
VotingAdapter(PullPushAdapter adapter, Serializable id)

Method Summary

void
addVoteListener(VotingListener listener)
Adds voting listener.
void
block()
Blocks the channel until the ViewAccepted is invoked.
static String
getConsensusStr(int consensusType)
Convert consensus type into string representation.
byte[]
getState()
Get the channel state.
VotingAdapter.VoteResult
localVote(Object decree)
This method performs voting on the specific decree between all local voteListeners.
void
receive(Message msg)
Receive the message.
void
removeVoteListener(VotingListener listener)
Removes voting listener.
void
setState(byte[] state)
Set the channel state.
void
suspect(Address suspected)
Callback for notification that one node is suspected
void
viewAccepted(View newView)
Callback for notification about the new view of the group.
boolean
vote(Object decree, int consensusType, long timeout)
Performs actual voting on the VoteChannel using the JGroups facilities for communication.
boolean
vote(Object decree, long timeout)
Vote on the specified decree requiring all nodes to vote.

Field Details

VOTE_ALL

public static final int VOTE_ALL
This consensus type means that at least one positive vote and no negative votes are required for the voting to succeed.

Field Value:
1


VOTE_ANY

public static final int VOTE_ANY
This consensus type means that at least one positive vote is required for the voting to succeed.

Field Value:
0


VOTE_MAJORITY

public static final int VOTE_MAJORITY
This consensus type means that number of positive votes should be greater than number of negative votes.

Field Value:
2


log

protected Log log

Constructor Details

VotingAdapter

public VotingAdapter(Channel channel)
Creates an instance of the VoteChannel that uses JGroups for communication between group members.

Parameters:
channel - JGroups channel.


VotingAdapter

public VotingAdapter(PullPushAdapter adapter,
                     Serializable id)

Method Details

addVoteListener

public void addVoteListener(VotingListener listener)
Adds voting listener.


block

public void block()
Blocks the channel until the ViewAccepted is invoked.
Specified by:
block in interface MembershipListener


getConsensusStr

public static String getConsensusStr(int consensusType)
Convert consensus type into string representation. This method is useful for debugginf.

Parameters:
consensusType - type of the consensus.

Returns:
string representation of the consensus type.


getState

public byte[] getState()
Get the channel state.
Specified by:
getState in interface MessageListener

Returns:
always null, we do not have any group-shared state.


localVote

public VotingAdapter.VoteResult localVote(Object decree)
This method performs voting on the specific decree between all local voteListeners.


receive

public void receive(Message msg)
Receive the message. All messages are ignored.
Specified by:
receive in interface MessageListener

Parameters:
msg - message to check.


removeVoteListener

public void removeVoteListener(VotingListener listener)
Removes voting listener.


setState

public void setState(byte[] state)
Set the channel state. We do nothing here.
Specified by:
setState in interface MessageListener


suspect

public void suspect(Address suspected)
Callback for notification that one node is suspected
Specified by:
suspect in interface MembershipListener


viewAccepted

public void viewAccepted(View newView)
Callback for notification about the new view of the group.
Specified by:
viewAccepted in interface MembershipListener


vote

public boolean vote(Object decree,
                    int consensusType,
                    long timeout)
            throws ChannelException
Performs actual voting on the VoteChannel using the JGroups facilities for communication.


vote

public boolean vote(Object decree,
                    long timeout)
            throws ChannelException
Vote on the specified decree requiring all nodes to vote.

Parameters:
decree - decree on which nodes should vote.
timeout - time during which nodes can vote.

Returns:
true if nodes agreed on a decree, otherwise false

Throws:
ChannelException - if something went wrong.


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