twophasevotingadapter.java

来自「JGRoups源码」· Java 代码 · 共 165 行

package org.jgroups.blocks;

import org.jgroups.ChannelException;

/**
 * This adapter introduces simple two-phase voting on a specified decree. All
 * nodes in the group receive a decree in "prepare" phase where they expres
 * their opinion on the decree. If all nodes voted positively on decree, next
 * phase "commit" fixes changes that were made in "prepare" phase, otherwise 
 * changes are canceled in "abort" phase. 
 * 
 * @author Roman Rokytskyy ([e-mail])
 * @author Robert Schaffar-Taurok ([e-mail])
 * @version $Id: TwoPhaseVotingAdapter.java,v 1.4 2005/06/08 15:56:54 publicnmi Exp $
 */
public class TwoPhaseVotingAdapter {

    private final VotingAdapter voteChannel;

    /**
     * Creats an instance of the class.
     * @param voteChannel the channel that will be used for voting.
     */
    public TwoPhaseVotingAdapter(VotingAdapter voteChannel) {
        this.voteChannel = voteChannel;
    }

    /**
     * Wraps actual listener with the VoteChannelListener and adds to the
     * voteChannel
     */
    public void addListener(TwoPhaseVotingListener listener) {
        voteChannel.addVoteListener(new TwoPhaseVoteWrapper(listener));
    }

    /**
     * Removes the listener from the voteChannel
     */
    public void removeListener(TwoPhaseVotingListener listener) {
        voteChannel.removeVoteListener(new TwoPhaseVoteWrapper(listener));
    }

    /**
     * Performs the two-phase voting on the decree. After the voting each
     * group member remains in the same state as others.
     */
    public boolean vote(Object decree, long timeout) throws ChannelException {
        return vote(decree, timeout, null);
    }

    /**
     * Performs the two-phase voting on the decree. After the voting each
     * group member remains in the same state as others.
     */
    public boolean vote(Object decree, long timeout, VoteResponseProcessor voteResponseProcessor) throws ChannelException {
        // wrap real decree
        TwoPhaseWrapper wrappedDecree = new TwoPhaseWrapper(decree);

        // check the decree acceptance
        try {
            if (voteChannel.vote(wrappedDecree, timeout / 3, voteResponseProcessor)) {
                wrappedDecree.commit();

                // try to commit decree
                if (!voteChannel.vote(wrappedDecree, timeout / 3, voteResponseProcessor)) {
                    // strange, should fail during prepare... abort all
                    wrappedDecree.abort();
                    voteChannel.vote(wrappedDecree, timeout / 3, voteResponseProcessor);
                    return false;
                } else
                        return true;

            } else {
                // somebody is not accepting the decree... abort
                wrappedDecree.abort();
                voteChannel.vote(wrappedDecree, timeout / 3, voteResponseProcessor);
                return false;
            }
        } catch(ChannelException chex) {
            wrappedDecree.abort();
            voteChannel.vote(wrappedDecree, timeout / 3, voteResponseProcessor);
            throw chex;
        }
    }
 
    
    /**
     * @return Returns the voteChannel.
     */
    public VotingAdapter getVoteChannel() {
        return voteChannel;
    }
    
    public static class TwoPhaseVoteWrapper implements VotingListener {
    
        private final TwoPhaseVotingListener listener;
    
        public TwoPhaseVoteWrapper(TwoPhaseVotingListener listener) {
            this.listener = listener;
        }
    
        public boolean vote(Object decree) throws VoteException {
            if (!(decree instanceof TwoPhaseWrapper))
                throw new VoteException("Not my type of decree. Ignore me.");
    
            TwoPhaseWrapper wrapper = (TwoPhaseWrapper)decree;
    
            // invoke the corresponding operation
            if (wrapper.isPrepare())
                return listener.prepare(wrapper.getDecree());
            else
            if (wrapper.isCommit())
                return listener.commit(wrapper.getDecree());
            else {
                listener.abort(wrapper.getDecree());
                return false;
            }
        }
    
        /*
    
         This wrapper is completely equal to the object it wraps.
    
         Therefore the hashCode():int and equals(Object):boolean are
         simply delegated to the wrapped code.
    
         */
    
        public int hashCode() {	return listener.hashCode(); }
        public boolean equals(Object other) { return listener.equals(other); }
    }

    /**
     * Wrapper of the decree to voting decree.
     */
    public static class TwoPhaseWrapper implements java.io.Serializable {
        private static final int PREPARE = 0;
        private static final int COMMIT = 1;
        private static final int ABORT = 2;
    
        public TwoPhaseWrapper(Object decree) {
            setDecree(decree);
            setType(PREPARE);
        }
    
        private Object decree;
        private int type;
    
        public Object getDecree(){ return decree; }
        public void setDecree(Object decree){ this.decree = decree; }
    
        private int getType() { return type; }
        private void setType(int type) { this.type = type; }
        private boolean isType(int type) { return this.type == type; }
    
        public boolean isPrepare() { return isType(PREPARE); }
        public boolean isCommit() { return isType(COMMIT); }
        public boolean isAbort() { return isType(ABORT); }
    
        public void commit() { setType(COMMIT); }
        public void abort() { setType(ABORT); }
    
        public String toString() { return decree.toString(); }
    }
}