Package org.jgroups.blocks

Class VotingAdapter

java.lang.Object
org.jgroups.blocks.VotingAdapter
All Implemented Interfaces:
VoteResponseProcessor, MembershipListener, MessageListener
public class VotingAdapter extends 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.

Version:
$Id: VotingAdapter.java,v 1.10 2006/09/27 12:42:53 belaban Exp $
Author:
Roman Rokytskyy (rrokytskyy@acm.org), Robert Schaffar-Taurok (robert@fusion.at)

  • Field Details

    • 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:

    • 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:

    • 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:

    • log

      protected final org.apache.commons.logging.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

    • getMembers

      public Collection getMembers()

    • addMembershipListener

      public void addMembershipListener(MembershipListener l)

    • removeMembershipListener

      public void removeMembershipListener(MembershipListener l)

    • vote

      public boolean vote(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(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, 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
      Parameters:
      state -

    • 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.

    • vote

      public boolean vote(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(Object decree)
      This method performs voting on the specific decree between all local voteListeners.

    • 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.