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JGroups RAFT implementation
There is a newer version: 1.0.14.Final
package org.jgroups.raft.util;

import org.jgroups.Address;

import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.function.BiConsumer;

/**
 * Keeps track of next_index and match_index for each cluster member (excluding this leader).
 * Used to (1) compute the commit_index and (2) to resend log entries to members which haven't yet seen them.
 * Only created on the leader
 * @author Bela Ban
 * @since  0.1
 */
public class CommitTable {
    protected final ConcurrentMap map=new ConcurrentHashMap<>();


    public CommitTable(List members, int next_index) {
        adjust(members, next_index);
    }

    public Set keys() {return map.keySet();}

    public void adjust(List members, int next_index) {
        map.keySet().retainAll(members);
        // entry is only created if mbr is not in map, reducing unneeded creations
        members.forEach(mbr -> map.computeIfAbsent(mbr, k -> new Entry(next_index)));
    }

    public CommitTable update(Address member, int match_index, int next_index, int commit_index, boolean single_resend) {
        Entry entry=map.get(member);
        if(entry == null)
            return this;
        entry.match_index=Math.max(match_index, entry.match_index);
        entry.next_index=Math.max(1, next_index);
        entry.commit_index=Math.max(entry.commit_index, commit_index);
        entry.send_single_msg=single_resend;
        return this;
    }

    public boolean snapshotInProgress(Address mbr, boolean flag) {
        Entry entry=map.get(mbr);
        return entry != null && entry.snapshotInProgress(flag);
    }


    /** Applies a function to all elements of the commit table */
    public void forEach(BiConsumer function) {
        for(Map.Entry entry: map.entrySet()) {
            Entry val=entry.getValue();
            if(!val.snapshot_in_progress)
                function.accept(entry.getKey(), val);
        }
    }

    @Override
    public String toString() {
        StringBuilder sb=new StringBuilder();
        for(Map.Entry entry: map.entrySet())
            sb.append(entry.getKey()).append(": ").append(entry.getValue()).append("\n");
        return sb.toString();
    }



    public static class Entry {
        // the next index to send; initialized to last_appended +1
        protected int     next_index;

        // the index of the highest entry known to be replicated to the member
        protected int     match_index;

        // the commit index of the given member
        protected int     commit_index;

        // set when a snapshot is being installed
        protected boolean snapshot_in_progress;

        // set to true when next_index was decremented, so we only send a single entry on the next resend interval;
        // set to false when we receive an AppendEntries(true) response
        protected boolean send_single_msg;

        public Entry(int next_index) {this.next_index=next_index;}

        public int     nextIndex()                     {return next_index;}
        public Entry   nextIndex(int idx)              {next_index=idx; return this;}
        public int     matchIndex()                    {return match_index;}
        public Entry   matchIndex(int idx)             {this.match_index=idx; return this;}
        public int     commitIndex()                   {return commit_index;}
        public Entry   commitIndex(int idx)            {this.commit_index=idx; return this;}
        public boolean sendSingleMessage()             {return send_single_msg;}
        public Entry   sendSingleMessage(boolean flag) {this.send_single_msg=flag; return this;}

        public boolean snapshotInProgress(boolean flag) {
            if(snapshot_in_progress == flag)
                return false;
            snapshot_in_progress=flag;
            return true;
        }

        @Override public String toString() {
            StringBuilder sb=new StringBuilder().append("match-index=").append(match_index);
            sb.append(", next-index=").append(next_index).append(", commit-index=").append(commit_index);
            if(snapshot_in_progress)
                sb.append(" [snapshotting]");
            if(send_single_msg)
                sb.append(" [send-single-msg]");
            return sb.toString();
        }
    }

}