org.jrobin.core.RrdMemoryBackend Maven / Gradle / Ivy
Show all versions of jrobin Show documentation
/*******************************************************************************
* 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.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Backend to be used to store all RRD bytes in memory.
*/
public class RrdMemoryBackend extends RrdBackend {
private static final ReadWriteLock m_readWritelock = new ReentrantReadWriteLock();
private static final Lock m_readLock = m_readWritelock.readLock();
private static final Lock m_writeLock = m_readWritelock.writeLock();
private byte[] buffer = new byte[0];
protected RrdMemoryBackend(String path) {
super(path);
}
protected void write(final long offset, final byte[] b) {
m_writeLock.lock();
try {
int pos = (int) offset;
for (final byte singleByte : b) {
buffer[pos++] = singleByte;
}
} finally {
m_writeLock.unlock();
}
}
protected void read(final long offset, final byte[] b) throws IOException {
m_readLock.lock();
try {
int pos = (int) offset;
if (pos + b.length <= buffer.length) {
for (int i = 0; i < b.length; i++) {
b[i] = buffer[pos++];
}
}
else {
throw new IOException("Not enough bytes available in memory " + getPath());
}
} finally {
m_readLock.unlock();
}
}
/**
* Returns the number of RRD bytes held in memory.
*
* @return Number of all RRD bytes.
*/
public long getLength() {
m_readLock.lock();
try {
return buffer.length;
} finally {
m_readLock.unlock();
}
}
/**
* Reserves a memory section as a RRD storage.
*
* @param newLength Number of bytes held in memory.
* @throws IOException Thrown in case of I/O error.
*/
protected void setLength(final long newLength) throws IOException {
m_writeLock.lock();
try {
if (newLength > Integer.MAX_VALUE) {
throw new IOException("Cannot create this big memory backed RRD");
}
buffer = new byte[(int) newLength];
} finally {
m_writeLock.unlock();
}
}
/**
* This method is required by the base class definition, but it does not
* releases any memory resources at all.
*/
public void close() {
// NOP
}
/**
* This method is overridden to disable high-level caching in frontend JRobin classes.
*
* @return Always returns false. There is no need to cache anything in high-level classes
* since all RRD bytes are already in memory.
*/
protected boolean isCachingAllowed() {
return false;
}
}