/*******************************************************************************
* 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.channels.FileLock;
import java.nio.channels.FileChannel;
/**
* JRobin backend which is used to store RRD data to ordinary files on the disk. This backend
* is SAFE: it locks the underlying RRD file during update/fetch operations, and caches only static
* parts of a RRD file in memory. Therefore, this backend is safe to be used when RRD files should
* be shared between several JVMs at the same time. However, this backend is a little bit slow
* since it does not use fast java.nio.* package (it's still based on the RandomAccessFile class).
*/
public class RrdSafeFileBackend extends RrdFileBackend {
private static final Counters counters = new Counters();
private FileLock m_lock;
/**
* Creates RrdFileBackend object for the given file path, backed by RandomAccessFile object.
*
* @param path Path to a file
* @throws IOException Thrown in case of I/O error
*/
public RrdSafeFileBackend(final String path, final long lockWaitTime, final long lockRetryPeriod) throws IOException {
super(path, false);
try {
lockFile(lockWaitTime, lockRetryPeriod);
}
catch (final IOException ioe) {
super.close();
throw ioe;
}
}
private void lockFile(final long lockWaitTime, final long lockRetryPeriod) throws IOException {
final long entryTime = System.currentTimeMillis();
final FileChannel channel = file.getChannel();
m_lock = channel.tryLock(0, Long.MAX_VALUE, false);
if (m_lock != null) {
counters.registerQuickLock();
return;
}
do {
try {
Thread.sleep(lockRetryPeriod);
}
catch (final InterruptedException e) {
Thread.currentThread().interrupt();
}
m_lock = channel.tryLock(0, Long.MAX_VALUE, false);
if (m_lock != null) {
counters.registerDelayedLock();
return;
}
} while (System.currentTimeMillis() - entryTime <= lockWaitTime);
counters.registerError();
throw new IOException("Could not obtain exclusive m_lock on file: " + getPath() + "] after " + lockWaitTime + " milliseconds");
}
public void close() throws IOException {
try {
if (m_lock != null) {
m_lock.release();
m_lock = null;
counters.registerUnlock();
}
}
finally {
super.close();
}
}
/**
* Defines the caching policy for this backend.
*
* @return <code>false</code>
*/
protected boolean isCachingAllowed() {
return false;
}
public static String getLockInfo() {
return counters.getInfo();
}
static class Counters {
long locks, quickLocks, unlocks, locked, errors;
synchronized void registerQuickLock() {
locks++;
quickLocks++;
locked++;
}
synchronized void registerDelayedLock() {
locks++;
locked++;
}
synchronized void registerUnlock() {
unlocks++;
locked--;
}
synchronized void registerError() {
errors++;
}
synchronized String getInfo() {
return "LOCKS=" + locks + ", " + "UNLOCKS=" + unlocks + ", " +
"DELAYED_LOCKS=" + (locks - quickLocks) + ", " + "LOCKED=" + locked + ", " +
"ERRORS=" + errors;
}
}
}