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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.
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/*
 * Copyright (c) 2002-2015 "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 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel;

import java.io.IOException;

import org.neo4j.kernel.impl.transaction.tracing.LogAppendEvent;
import org.neo4j.kernel.impl.transaction.tracing.LogRotateEvent;
import org.neo4j.kernel.impl.transaction.log.LogFile;
import org.neo4j.kernel.impl.transaction.log.LogRotation;
import org.neo4j.kernel.impl.transaction.log.LogRotationControl;
import org.neo4j.kernel.impl.util.StringLogger;
import org.neo4j.kernel.logging.Logging;

/**
 * Default implementation of the LogRotation interface.
 */
public class LogRotationImpl
    implements LogRotation
{
    private final LogRotation.Monitor monitor;
    private final LogFile logFile;
    private final LogRotationControl logRotationControl;
    private final KernelHealth kernelHealth;
    private final StringLogger msgLog;

    public LogRotationImpl( Monitor monitor, LogFile logFile,
            LogRotationControl logRotationControl, KernelHealth kernelHealth, Logging logging )
    {
        this.monitor = monitor;
        this.logFile = logFile;
        this.logRotationControl = logRotationControl;
        this.kernelHealth = kernelHealth;

        msgLog = logging.getMessagesLog( getClass() );
    }

    @Override
    public boolean rotateLogIfNeeded( LogAppendEvent logAppendEvent ) throws IOException
    {
        if ( logFile.rotationNeeded() )
        {
            /* We synchronize on the writer because we want to have a monitor that another thread
             * doing force (think batching of writes), such that it can't see a bad state of the writer
             * even when rotating underlying channels.
             */
            boolean rotated;
            synchronized ( logFile )
            {
                if ( rotated = logFile.rotationNeeded() )
                {
                    try ( LogRotateEvent rotateEvent = logAppendEvent.beginLogRotate() )
                    {
                        doRotate();
                    }
                }
            }

            return rotated;
        }

        return false;
    }

    @Override
    public void rotateLogFile() throws IOException
    {
        synchronized ( logFile )
        {
            doRotate();
        }
    }

    private void doRotate() throws IOException
    {
        long currentVersion = logFile.currentLogVersion();

        monitor.startedRotating( currentVersion );

        /*
         * Check kernel health before going into waiting for transactions to be closed, to avoid
         * getting into a scenario where we would await a condition that would potentially never happen.
         */
        kernelHealth.assertHealthy( IOException.class );

        /*
         * First we flush the store. If we fail now or during the flush, on recovery we'll discover
         * the current log file and replay it. Everything will be ok.
         */
        msgLog.info( PrintFormat.prefix( currentVersion ) + " Awaiting all transactions closed..." );
        logRotationControl.awaitAllTransactionsClosed();
        msgLog.info( PrintFormat.prefix( currentVersion ) + " Starting store flush..." );
        logRotationControl.forceEverything();

        /*
         * In order to rotate the current log file safely we need to assert that the kernel is still
         * at full health. In case of a panic this rotation will be aborted, which is the safest alternative
         * so that the next recovery will have a chance to repair the damages.
         */
        kernelHealth.assertHealthy( IOException.class );

        msgLog.info( PrintFormat.prefix( currentVersion ) + " Preparing new log file..." );
        logFile.rotate();

        monitor.finishedRotating( currentVersion );
    }
}