org.jgroups.blocks
Class VotingAdapter

java.lang.Object
  org.jgroups.blocks.VotingAdapter

All Implemented Interfaces:

VoteResponseProcessor, MembershipListener, MessageListener

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

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 VoteException. 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), Robert Schaffar-Taurok (robert@fusion.at)

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

protected Log	log
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.

Constructor Summary

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

VotingAdapter(PullPushAdapter adapter, java.io.Serializable id)

Method Summary

void	addMembershipListener(MembershipListener l)
void	addVoteListener(VotingListener listener) Adds voting listener.
void	block() Blocks the channel until the ViewAccepted is invoked.
static java.lang.String	getConsensusStr(int consensusType) Convert consensus type into string representation.
java.util.Collection	getMembers()
byte[]	getState() Get the channel state.
VotingAdapter.VoteResult	localVote(java.lang.Object decree) This method performs voting on the specific decree between all local voteListeners.
boolean	processResponses(RspList responses, int consensusType, java.lang.Object decree) Processes the response list and makes a decision according to the type of the consensus for current voting.
void	receive(Message msg) Receive the message.
void	removeMembershipListener(MembershipListener l)
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(java.lang.Object decree, int consensusType, long timeout) Performs actual voting on the VoteChannel using the JGroups facilities for communication.
boolean	vote(java.lang.Object decree, int consensusType, long timeout, VoteResponseProcessor voteResponseProcessor) Performs actual voting on the VoteChannel using the JGroups facilities for communication.
boolean	vote(java.lang.Object decree, long timeout) Vote on the specified decree requiring all nodes to vote.
boolean	vote(java.lang.Object decree, long timeout, VoteResponseProcessor voteResponseProcessor) Vote on the specified decree requiring all nodes to vote.

Methods inherited from class java.lang.Object

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

Field Detail

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

log

protected final Log log

Constructor Detail

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,
                     java.io.Serializable id)

Method Detail

getMembers

public java.util.Collection getMembers()

addMembershipListener

public void addMembershipListener(MembershipListener l)

removeMembershipListener

public void removeMembershipListener(MembershipListener l)

vote

public boolean vote(java.lang.Object decree,
                    int consensusType,
                    long timeout)
             throws ChannelException

Performs actual voting on the VoteChannel using the JGroups facilities for communication.

Throws:

ChannelException

vote

public boolean vote(java.lang.Object decree,
                    int consensusType,
                    long timeout,
                    VoteResponseProcessor voteResponseProcessor)
             throws ChannelException

Performs actual voting on the VoteChannel using the JGroups facilities for communication.

Throws:

ChannelException

processResponses

public boolean processResponses(RspList responses,
                                int consensusType,
                                java.lang.Object decree)
                         throws ChannelException

Processes the response list and makes a decision according to the type of the consensus for current voting.

Note: we do not support voting in case of Byzantine failures, i.e. when the node responds with the fault message.

Specified by:

processResponses in interface VoteResponseProcessor

Parameters:

responses - The responses

consensusType - The consensusType of the vote

decree - The vote decree

Returns:

boolean

Throws:

ChannelException

viewAccepted

public void viewAccepted(View newView)

Callback for notification about the new view of the group.

Specified by:

viewAccepted in interface MembershipListener

suspect

public void suspect(Address suspected)

Callback for notification that one node is suspected

Specified by:

suspect in interface MembershipListener

block

public void block()

Blocks the channel until the ViewAccepted is invoked.

Specified by:

block in interface MembershipListener

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.

receive

public void receive(Message msg)

Receive the message. All messages are ignored.

Specified by:

receive in interface MessageListener

Parameters:

msg - message to check.

setState

public void setState(byte[] state)

Set the channel state. We do nothing here.

Specified by:

setState in interface MessageListener

vote

public boolean vote(java.lang.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.

vote

public boolean vote(java.lang.Object decree,
                    long timeout,
                    VoteResponseProcessor voteResponseProcessor)
             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.

voteResponseProcessor - processor which will be called for every response that is received.

Returns:

true if nodes agreed on a decree, otherwise false

Throws:

ChannelException - if something went wrong.

addVoteListener

public void addVoteListener(VotingListener listener)

Adds voting listener.

removeVoteListener

public void removeVoteListener(VotingListener listener)

Removes voting listener.

localVote

public VotingAdapter.VoteResult localVote(java.lang.Object decree)

This method performs voting on the specific decree between all local voteListeners.

getConsensusStr

public static java.lang.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.