/*******************************************************************************
* Copyright (c) 2001-2005 Sasa Markovic and Ciaran Treanor.
* Copyright (c) 2011 The OpenNMS Group, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*******************************************************************************/
package org.jrobin.core;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import engine.misc.DeallocationHelper;
/**
* JRobin backend which is used to store RRD data to ordinary disk files by
* using fast java.nio.* package. This is the default backend engine since
* JRobin 1.4.0.
*/
@SuppressWarnings("restriction")
public class RrdNioBackend extends RrdFileBackend {
private final SyncManager m_syncManager;
private MappedByteBuffer m_byteBuffer = null;
private static final DeallocationHelper _dHelper = new DeallocationHelper();
/**
* Creates RrdFileBackend object for the given file path, backed by
* java.nio.* classes. This constructor will create a
* {@link SyncManager} for each instance, which is very inefficient.
* It is recommended that you instead use the
* {@link #RrdNioBackend(String, boolean, SyncManager)}
* constructor instead.
*
* @param path
* Path to a JRB file.
* @param readOnly
* True, if file should be open in a read-only mode. False
* otherwise
* @param syncPeriod
* How often (in seconds) to sync MMAP'd RRD data to disk
* @throws IOException
* Thrown in case of I/O error
*/
protected RrdNioBackend(final String path, final boolean readOnly, final int syncPeriod) throws IOException {
this(path, readOnly, new SyncManager(syncPeriod));
}
/**
* Creates RrdFileBackend object for the given file path, backed by
* java.nio.* classes.
*
* @param path
* Path to a file
* @param readOnly
* True, if file should be open in a read-only mode. False
* otherwise.
* @param syncManager
* An object for managing synchronization of NIO-backed RRDs,
* generally owned by the backend factory. If null, MMAP'd
* data will only be synchronized to disk upon unmap. Note
* that if the file is opened read-only, the SyncManager is
* ignored. {@link RrdNioBackend#unmapFile() unmapFile()}
* @throws IOException
* Thrown in case of I/O error
*/
protected RrdNioBackend(final String path, final boolean readOnly, final SyncManager syncManager) throws IOException {
super(path, readOnly);
m_syncManager = syncManager;
try {
mapFile();
} catch (final IOException ioe) {
stopSchedule();
super.close();
throw ioe;
}
}
private void mapFile() throws IOException {
if (!isReadOnly()) {
startSchedule();
}
final long length = getLength();
if (length > 0) {
final FileChannel.MapMode mapMode = isReadOnly() ? FileChannel.MapMode.READ_ONLY : FileChannel.MapMode.READ_WRITE;
m_byteBuffer = file.getChannel().map(mapMode, 0, length);
}
}
private void unmapFile() {
if (!isReadOnly()) {
stopSchedule();
}
if (m_byteBuffer != null) {
_dHelper.deallocate(m_byteBuffer);
m_byteBuffer = null;
}
}
private void startSchedule() {
if (m_syncManager != null) {
m_syncManager.add(this);
}
}
private synchronized void stopSchedule() {
if (m_syncManager != null) {
m_syncManager.remove(this);
}
sync();
}
@Override
protected void finalize() throws Throwable {
stopSchedule();
super.finalize();
}
/**
* Sets length of the underlying RRD file. This method is called only
* once, immediately after a new RRD file gets created.
*
* @param newLength
* Length of the RRD file
* @throws IOException
* Thrown in case of I/O error.
*/
protected synchronized void setLength(final long newLength) throws IOException {
unmapFile();
super.setLength(newLength);
mapFile();
}
/**
* Writes bytes to the underlying RRD file on the disk
*
* @param offset
* Starting file offset
* @param b
* Bytes to be written.
*/
protected synchronized void write(final long offset, final byte[] b) throws IOException {
if (m_byteBuffer != null) {
m_byteBuffer.position((int) offset);
m_byteBuffer.put(b);
} else {
throw new IOException("Write failed, file " + getPath() + " not mapped for I/O");
}
}
/**
* Reads a number of bytes from the RRD file on the disk
*
* @param offset
* Starting file offset
* @param b
* Buffer which receives bytes read from the file.
*/
protected synchronized void read(final long offset, final byte[] b) throws IOException {
if (m_byteBuffer != null) {
m_byteBuffer.position((int) offset);
m_byteBuffer.get(b);
} else {
throw new IOException("Read failed, file " + getPath() + " not mapped for I/O");
}
}
/**
* Closes the underlying RRD file.
*
* @throws IOException
* Thrown in case of I/O error
*/
public synchronized void close() throws IOException {
// cancel synchronization
try {
unmapFile();
} finally {
super.close();
}
}
/**
* This method forces all data cached in memory but not yet stored in the
* file, to be stored in it.
*/
protected synchronized void sync() {
if (m_byteBuffer != null) {
m_byteBuffer.force();
}
}
}