com.bigdata.relation.accesspath.UnsynchronizedUnboundedChunkBuffer Maven / Gradle / Ivy
/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
[email protected]
This program 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; version 2 of the License.
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, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Jun 20, 2008
*/
package com.bigdata.relation.accesspath;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;
import com.bigdata.striterator.EmptyChunkedIterator;
import com.bigdata.striterator.IChunkedOrderedIterator;
import com.bigdata.striterator.IKeyOrder;
/**
* An unsynchronized buffer backed by a fixed capacity array that migrates
* references onto an internal {@link Queue}, which may be drained by an
* {@link #iterator()}.
*
* This implementation is NOT thread-safe.
*
* @author Bryan Thompson
* @version $Id$
*
* @see TestUnsynchronizedUnboundedChunkBuffer
*/
public class UnsynchronizedUnboundedChunkBuffer extends
AbstractUnsynchronizedArrayBuffer {
/**
* The queue onto which chunks are evicted by {@link #overflow()}.
*/
private final Queue queue;
/**
* The order of the elements as they are added to the buffer (iff known).
*/
private final IKeyOrder keyOrder;
/**
* From the first element visited.
*
* TODO This is probably no longer required since the component type of the
* class is now declared in the constructor.
*/
private Class chunkClass = null;
/**
* @param capacity
* The capacity of the backing buffer.
* @param cls
* The component type of the backing array.
*/
public UnsynchronizedUnboundedChunkBuffer(final int capacity,
final Class cls) {
this(capacity, cls, null/* filter */, null/* keyOrder */);
}
/**
* @param capacity
* The capacity of the backing buffer.
* @param cls
* The component type of the backing array.
* @param filter
* Filter to keep elements out of the buffer (optional).
* @param keyOrder
* The order of the elements in the chunks written onto the
* buffer or null iff not known.
*/
public UnsynchronizedUnboundedChunkBuffer(final int capacity,
final Class cls,
final IElementFilter filter, final IKeyOrder keyOrder) {
super(capacity, cls, filter);
this.keyOrder = keyOrder;
queue = new LinkedBlockingQueue(/* unbounded capacity */);
}
/** Add the chunk to the target buffer. */
final protected void handleChunk(final E[] chunk) {
if (chunkClass == null) {
// Note the Class of the chunk for the snapshot iterator.
chunkClass = (Class) chunk.getClass();
}
queue.add(chunk);
}
/**
* Iterator drains chunks from a snapshot of the queue (shallow copy).
* Chunks are drained in a FIFO basis. The internal buffer is flushed onto a
* chunk on the queue before the snapshot is taken so that any buffered
* elements will appear in the snapshot.
*/
public IChunkedOrderedIterator iterator() {
overflow();
/*
* Snapshot the queue state and wrap as an iterator visiting chunks of
* elements.
*/
synchronized (queue) {
if (queue.isEmpty()) {
// Note: handles case where chunkClass is not defined.
return new EmptyChunkedIterator(keyOrder);
}
assert chunkClass != null;
final Iterator src = Arrays.asList(
(E[][]) queue.toArray((E[][]) java.lang.reflect.Array
.newInstance(chunkClass, 0/* size */))).iterator();
// wrap with the IChunkedOrderedIterator API.
return new ListOfChunksIterator(src, keyOrder);
}
}
/**
* Drains chunks from a queue. Chunks are drained in a FIFO basis.
*
* @author Bryan Thompson
* @version $Id$
*/
static private class ListOfChunksIterator implements
IChunkedOrderedIterator {
private final Iterator src;
private final IKeyOrder keyOrder;
/**
*
* @param src
* Iterator visiting dense chunks.
* @param keyOrder
* The order of the elements in the buffer or
* null iff not known.
*/
public ListOfChunksIterator(final Iterator src,
final IKeyOrder keyOrder) {
this.src = src;
this.keyOrder = keyOrder;
}
/** true iff open. */
private boolean open = true;
/** Index of the next element to visit in the current chunk. */
private int i = 0;
/**
* The current chunk or null if another chunk should be read from the
* queue.
*/
private E[] chunk;
public boolean hasNext() {
if (!open)
return false;
do {
if (chunk != null && i >= chunk.length) {
// chunk is exhausted.
chunk = null;
i = 0;
}
if (chunk == null) {
if(!src.hasNext()) {
// nothing left.
return false;
}
// another chunk.
chunk = src.next();
i = 0;
}
} while (chunk.length == 0); // skip empty chunks.
return true;
}
public E next() {
if (!hasNext())
throw new NoSuchElementException();
return chunk[i++];
}
public E[] nextChunk() {
if (!hasNext())
throw new NoSuchElementException();
final E[] ret;
if (i == 0) {
ret = chunk;
} else {
/*
* Create and return a new chunk[] containing only the elements
* remaining in the current iterator.
*/
final int remaining = chunk.length - i;
/*
* Dynamically instantiation an array of the same component type
* as the objects that we are visiting.
*/
ret = (E[]) java.lang.reflect.Array.newInstance(chunk.getClass()
.getComponentType(), remaining);
System.arraycopy(chunk, i, ret, 0, remaining);
}
// indicate that all statements have been consumed.
chunk = null;
i = 0;
return ret;
}
/**
* @throws UnsupportedOperationException
*/
public void remove() {
throw new UnsupportedOperationException();
}
public void close() {
open = false;
}
public IKeyOrder getKeyOrder() {
return keyOrder;
}
public E[] nextChunk(final IKeyOrder keyOrder) {
if (keyOrder == null)
throw new IllegalArgumentException();
final E[] chunk = nextChunk();
if (!keyOrder.equals(getKeyOrder())) {
/*
* Sort into the required order.
*
* Note: Since this iterator is supposed to have snapshot
* semantics the chunk is cloned so that the sort does not
* disturb the source data.
*/
Arrays.sort(chunk.clone(), 0, chunk.length, keyOrder.getComparator());
}
return chunk;
}
}
}