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TermState.java
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TermState.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.coreedge.raft.state.term;
import java.io.IOException;
import org.neo4j.coreedge.raft.state.SafeStateMarshal;
import org.neo4j.storageengine.api.ReadableChannel;
import org.neo4j.storageengine.api.WritableChannel;
public class TermState
{
private long term = 0;
public TermState()
{
}
private TermState( long term )
{
this.term = term;
}
public long currentTerm()
{
return term;
}
/**
* Updates the term to a new value. This value is generally expected, but not required, to be persisted. Consecutive
* calls to this method should always have monotonically increasing arguments, thus maintaining the raft invariant
* that the term is always non-decreasing. {@link IllegalArgumentException} can be thrown if an invalid value is
* passed as argument.
*
* @param newTerm The new value.
*/
public boolean update( long newTerm )
{
failIfInvalid( newTerm );
boolean changed = term != newTerm;
term = newTerm;
return changed;
}
/**
* This method implements the invariant of this class, that term never transitions to lower values. If
* newTerm is lower than the term already stored in this class, it will throw an
* {@link IllegalArgumentException}.
*/
private void failIfInvalid( long newTerm )
{
if ( newTerm < term )
{
throw new IllegalArgumentException( "Cannot move to a lower term" );
}
}
public static class Marshal extends SafeStateMarshal<TermState>
{
@Override
public void marshal( TermState termState, WritableChannel channel ) throws IOException
{
channel.putLong( termState.currentTerm() );
}
@Override
protected TermState unmarshal0( ReadableChannel channel ) throws IOException
{
return new TermState( channel.getLong() );
}
@Override
public TermState startState()
{
return new TermState();
}
@Override
public long ordinal( TermState state )
{
return state.currentTerm();
}
}
@Override
public String toString()
{
return "TermState{" +
"term=" + term +
'}';
}
}