/* The currrent state of a checkpoint object.

@Copyright (c) 2005-2013 The Regents of the University of California.
All rights reserved.

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 */
package ptolemy.backtrack;

import java.util.LinkedList;
import java.util.List;

///////////////////////////////////////////////////////////////////
//// CheckpointState

/**
 The current state of a checkpoint object. A checkpoint object stores its
 complete state in its <tt>CheckpointState</tt> object. Different checkpoint
 objects may share the same state, and hence they represent the same
 checkpoint entity.
 <p>
 When two checkpoint objects are merged, they exchange their states and
 compute the union of the two.

 @author Thomas Feng
 @version $Id: CheckpointState.java 65763 2013-03-07 01:54:37Z cxh $
 @since Ptolemy II 5.1
 @Pt.ProposedRating Red (tfeng)
 @Pt.AcceptedRating Red (tfeng)
 */
public class CheckpointState {
    ///////////////////////////////////////////////////////////////////
    ////                         public methods                    ////

    /** Create a new checkpoint, and return the new timestamp.
     *
     *  @return The new timestamp.
     */
    public long createCheckpoint() {
        return ++_currentTimestamp;
    }

    /** Get the list of all the monitored objects.
     *
     *  @return The list of all the monitored objects.
     */
    public List<Rollbackable> getMonitoredObjects() {
        return _monitoredObjects;
    }

    /** Get the current timestamp.
     *
     *  @return The current timestamp.
     */
    public long getTimestamp() {
        return _currentTimestamp;
    }

    ///////////////////////////////////////////////////////////////////
    ////                       private fields                      ////

    /** The current timestamp. It is static, so different checkpoint states use
     *  different timestamps, and the timestamps are always increasing in the
     *  time line.
     */
    private static long _currentTimestamp = 0;

    /** The list of objects monitored by the checkpoint object.
     */
    private List<Rollbackable> _monitoredObjects = new LinkedList<Rollbackable>();
}