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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.index.sasi.utils;
import java.io.Closeable;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel.MapMode;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.io.util.ChannelProxy;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.io.util.RandomAccessReader;
import com.google.common.annotations.VisibleForTesting;
public class MappedBuffer implements Closeable
{
private final MappedByteBuffer[] pages;
private long position, limit;
private final long capacity;
private final int pageSize, sizeBits;
private MappedBuffer(MappedBuffer other)
{
this.sizeBits = other.sizeBits;
this.pageSize = other.pageSize;
this.position = other.position;
this.limit = other.limit;
this.capacity = other.capacity;
this.pages = other.pages;
}
public MappedBuffer(RandomAccessReader file)
{
this(file.getChannel(), 30);
}
public MappedBuffer(ChannelProxy file)
{
this(file, 30);
}
@VisibleForTesting
protected MappedBuffer(ChannelProxy file, int numPageBits)
{
if (numPageBits > Integer.SIZE - 1)
throw new IllegalArgumentException("page size can't be bigger than 1G");
sizeBits = numPageBits;
pageSize = 1 << sizeBits;
position = 0;
limit = capacity = file.size();
pages = new MappedByteBuffer[(int) (file.size() / pageSize) + 1];
try
{
long offset = 0;
for (int i = 0; i < pages.length; i++)
{
long pageSize = Math.min(this.pageSize, (capacity - offset));
pages[i] = file.map(MapMode.READ_ONLY, offset, pageSize);
offset += pageSize;
}
}
finally
{
file.close();
}
}
public int comparePageTo(long offset, int length, AbstractType comparator, ByteBuffer other)
{
return comparator.compare(getPageRegion(offset, length), other);
}
public long capacity()
{
return capacity;
}
public long position()
{
return position;
}
public MappedBuffer position(long newPosition)
{
if (newPosition < 0 || newPosition > limit)
throw new IllegalArgumentException("position: " + newPosition + ", limit: " + limit);
position = newPosition;
return this;
}
public long limit()
{
return limit;
}
public MappedBuffer limit(long newLimit)
{
if (newLimit < position || newLimit > capacity)
throw new IllegalArgumentException();
limit = newLimit;
return this;
}
public long remaining()
{
return limit - position;
}
public boolean hasRemaining()
{
return remaining() > 0;
}
public byte get()
{
return get(position++);
}
public byte get(long pos)
{
return pages[getPage(pos)].get(getPageOffset(pos));
}
public short getShort()
{
short value = getShort(position);
position += 2;
return value;
}
public short getShort(long pos)
{
if (isPageAligned(pos, 2))
return pages[getPage(pos)].getShort(getPageOffset(pos));
int ch1 = get(pos) & 0xff;
int ch2 = get(pos + 1) & 0xff;
return (short) ((ch1 << 8) + ch2);
}
public int getInt()
{
int value = getInt(position);
position += 4;
return value;
}
public int getInt(long pos)
{
if (isPageAligned(pos, 4))
return pages[getPage(pos)].getInt(getPageOffset(pos));
int ch1 = get(pos) & 0xff;
int ch2 = get(pos + 1) & 0xff;
int ch3 = get(pos + 2) & 0xff;
int ch4 = get(pos + 3) & 0xff;
return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + ch4);
}
public long getLong()
{
long value = getLong(position);
position += 8;
return value;
}
public long getLong(long pos)
{
// fast path if the long could be retrieved from a single page
// that would avoid multiple expensive look-ups into page array.
return (isPageAligned(pos, 8))
? pages[getPage(pos)].getLong(getPageOffset(pos))
: ((long) (getInt(pos)) << 32) + (getInt(pos + 4) & 0xFFFFFFFFL);
}
public ByteBuffer getPageRegion(long position, int length)
{
if (!isPageAligned(position, length))
throw new IllegalArgumentException(String.format("range: %s-%s wraps more than one page", position, length));
ByteBuffer slice = pages[getPage(position)].duplicate();
int pageOffset = getPageOffset(position);
slice.position(pageOffset).limit(pageOffset + length);
return slice;
}
public MappedBuffer duplicate()
{
return new MappedBuffer(this);
}
public void close()
{
if (!FileUtils.isCleanerAvailable)
return;
/*
* Try forcing the unmapping of pages using undocumented unsafe sun APIs.
* If this fails (non Sun JVM), we'll have to wait for the GC to finalize the mapping.
* If this works and a thread tries to access any page, hell will unleash on earth.
*/
try
{
for (MappedByteBuffer segment : pages)
FileUtils.clean(segment);
}
catch (Exception e)
{
// This is not supposed to happen
}
}
private int getPage(long position)
{
return (int) (position >> sizeBits);
}
private int getPageOffset(long position)
{
return (int) (position & pageSize - 1);
}
private boolean isPageAligned(long position, int length)
{
return pageSize - (getPageOffset(position) + length) > 0;
}
}