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JSimpleDB classes relating to the key/value store API.
There is a newer version: 3.6.1

/*
 * Copyright (C) 2015 Archie L. Cobbs. All rights reserved.
 */

package org.jsimpledb.kv.mvcc;

import java.io.Closeable;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import org.jsimpledb.kv.CloseableKVStore;

/**
 * Represents one {@link SnapshotKVDatabase} MVCC version.
 *
 * 
 * Information included:
 *  

 *  MVCC version number
 *  {@link CloseableKVStore} snapshot
 *  Open transactions based on this version
 *  The {@link Writes} of the transaction that was committed on top of this version, if any
 *  
 */
public class SnapshotVersion implements Closeable {

    private final long version;
    private final SnapshotRefs snapshotRefs;
    private final HashSet openTransactions = new HashSet<>(2);

    private Writes committedWrites;
    private boolean closed;

    /**
     * Constructor.
     *
     * @param version version number
     * @param snapshot database snapshot
     */
    SnapshotVersion(long version, CloseableKVStore snapshot) {
        this.version = version;
        this.snapshotRefs = new SnapshotRefs(snapshot);
    }

    /**
     * Get this instance's unique version number.
     *
     * @return MVCC version number
     */
    public long getVersion() {
        return this.version;
    }

    /**
     * Get the {@link SnapshotRefs} for this version's snapshot.
     *
     * @return {@link SnapshotRefs} for snapshot
     */
    public SnapshotRefs getSnapshotRefs() {
        return this.snapshotRefs;
    }

    /**
     * Get transactions based on this version's snapshot that are still open.
     *
     * @return immutable view of open transactions associated with this version
     */
    public Set getOpenTransactions() {
        return Collections.unmodifiableSet(this.openTransactions);
    }

    /**
     * Get the {@link Writes} of the transaction based on this version's snapshot that was eventually committed, if any.
     *
     * @return writes of the transaction committed on this version, or null if there is none
     */
    public Writes getCommittedWrites() {
        return this.committedWrites;
    }

// Closeable

    @Override
    public synchronized void close() {
        if (this.closed)
            return;
        this.snapshotRefs.unref();
        this.closed = true;
    }

// Package methods

    void addOpenTransaction(SnapshotKVTransaction tx) {
        this.openTransactions.add(tx);
    }

    void removeOpenTransaction(SnapshotKVTransaction tx) {
        this.openTransactions.remove(tx);
    }

    void setCommittedWrites(Writes committedWrites) {
        this.committedWrites = committedWrites;
    }

// Object

    @Override
    public String toString() {
        return this.getClass().getSimpleName()
          + "[vers=" + this.version
          + (!this.openTransactions.isEmpty() ? ",openTx=" + this.openTransactions : "")
          + (this.committedWrites != null ? ",writes=" + this.committedWrites : "")
          + "]";
    }
}