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StoreLocker.java
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StoreLocker.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 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 <http://www.gnu.org/licenses/>.
*/
package org.neo4j.kernel.internal;
import java.io.File;
import java.io.IOException;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import org.neo4j.io.fs.FileSystemAbstraction;
import org.neo4j.io.fs.StoreChannel;
import org.neo4j.kernel.StoreLockException;
public class StoreLocker
{
public static final String STORE_LOCK_FILENAME = "store_lock";
private final FileSystemAbstraction fileSystemAbstraction;
private FileLock storeLockFileLock;
private StoreChannel storeLockFileChannel;
public StoreLocker( FileSystemAbstraction fileSystemAbstraction )
{
this.fileSystemAbstraction = fileSystemAbstraction;
}
/**
* Obtains lock on store file so that we can ensure the store is not shared between database instances
* <p>
* Creates store dir if necessary, creates store lock file if necessary
*
* @throws StoreLockException if lock could not be acquired
*/
public void checkLock( File storeDir ) throws StoreLockException
{
File storeLockFile = new File( storeDir, STORE_LOCK_FILENAME );
try
{
if ( !fileSystemAbstraction.fileExists( storeLockFile ) )
{
fileSystemAbstraction.mkdirs( storeLockFile.getParentFile() );
}
}
catch ( IOException e )
{
String message = "Unable to create path for store dir: " + storeDir;
throw storeLockException( message, e );
}
try
{
storeLockFileChannel = fileSystemAbstraction.open( storeLockFile, "rw" );
storeLockFileLock = storeLockFileChannel.tryLock();
if ( storeLockFileLock == null )
{
String message = "Store and its lock file has been locked by another process: " + storeLockFile;
throw storeLockException( message, null );
}
}
catch ( OverlappingFileLockException | IOException e )
{
String message = "Unable to obtain lock on store lock file: " + storeLockFile;
throw storeLockException( message, e );
}
}
private StoreLockException storeLockException( String message, Exception e )
{
String help = "Please ensure no other process is using this database, and that the directory is writable " +
"(required even for read-only access)";
return new StoreLockException( message + ". " + help, e );
}
public void release() throws IOException
{
if ( storeLockFileLock != null )
{
storeLockFileLock.release();
storeLockFileLock = null;
}
if ( storeLockFileChannel != null )
{
storeLockFileChannel.close();
storeLockFileChannel = null;
}
}
}