hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/impls/TreeDiskOrderScanCursor.java

/*
 * Copyright 2009-2010 by The Regents of the University of California
 * Licensed 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 from
 * 
 *     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 edu.uci.ics.hyracks.storage.am.common.impls;

import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
import edu.uci.ics.hyracks.storage.am.common.api.ICursorInitialState;
import edu.uci.ics.hyracks.storage.am.common.api.ISearchPredicate;
import edu.uci.ics.hyracks.storage.am.common.api.ITreeIndexCursor;
import edu.uci.ics.hyracks.storage.am.common.api.ITreeIndexFrame;
import edu.uci.ics.hyracks.storage.am.common.api.ITreeIndexTupleReference;
import edu.uci.ics.hyracks.storage.am.common.ophelpers.MultiComparator;
import edu.uci.ics.hyracks.storage.common.buffercache.IBufferCache;
import edu.uci.ics.hyracks.storage.common.buffercache.ICachedPage;
import edu.uci.ics.hyracks.storage.common.file.BufferedFileHandle;

public class TreeDiskOrderScanCursor implements ITreeIndexCursor {

	private int tupleIndex = 0;
	private int fileId = -1;
	int currentPageId = -1;
	int maxPageId = -1;
	private ICachedPage page = null;
	private ITreeIndexFrame frame = null;
	private IBufferCache bufferCache = null;

	private ITreeIndexTupleReference frameTuple;

	public TreeDiskOrderScanCursor(ITreeIndexFrame frame) {
		this.frame = frame;
		this.frameTuple = frame.getTupleWriter().createTupleReference();
	}

	@Override
	public void close() throws Exception {
		page.releaseReadLatch();
		bufferCache.unpin(page);
		page = null;
	}

	@Override
	public ITreeIndexTupleReference getTuple() {
		return frameTuple;
	}

	@Override
	public ICachedPage getPage() {
		return page;
	}

	private boolean positionToNextLeaf(boolean skipCurrent)
			throws HyracksDataException {
		while ((frame.getLevel() != 0 || skipCurrent)
				&& (currentPageId <= maxPageId) || (frame.getTupleCount() == 0)) {
			currentPageId++;

			ICachedPage nextPage = bufferCache.pin(
					BufferedFileHandle.getDiskPageId(fileId, currentPageId),
					false);
			nextPage.acquireReadLatch();

			page.releaseReadLatch();
			bufferCache.unpin(page);

			page = nextPage;
			frame.setPage(page);
			tupleIndex = 0;
			skipCurrent = false;
		}
		if (currentPageId <= maxPageId)
			return true;
		else
			return false;
	}

	@Override
	public boolean hasNext() throws Exception {
		if (tupleIndex >= frame.getTupleCount()) {
			boolean nextLeafExists = positionToNextLeaf(true);
			if (nextLeafExists) {
				frameTuple.resetByTupleIndex(frame, tupleIndex);
				return true;
			} else {
				return false;
			}
		}

		frameTuple.resetByTupleIndex(frame, tupleIndex);
		return true;
	}

	@Override
	public void next() throws Exception {
		tupleIndex++;
	}

	@Override
	public void open(ICursorInitialState initialState,
			ISearchPredicate searchPred) throws HyracksDataException {
		// in case open is called multiple times without closing
		if (page != null) {
			page.releaseReadLatch();
			bufferCache.unpin(page);
		}

		page = initialState.getPage();
		tupleIndex = 0;
		frame.setPage(page);
		MultiComparator lowKeyCmp = searchPred.getLowKeyComparator();
		frameTuple.setFieldCount(lowKeyCmp.getFieldCount());
		boolean leafExists = positionToNextLeaf(false);
		if (!leafExists) {
			throw new HyracksDataException(
					"Failed to open disk-order scan cursor for tree index. Traget tree index has no leaves.");
		}
	}

	@Override
	public void reset() {
		tupleIndex = 0;
		currentPageId = -1;
		maxPageId = -1;
		page = null;
	}

	@Override
	public void setBufferCache(IBufferCache bufferCache) {
		this.bufferCache = bufferCache;
	}

	@Override
	public void setFileId(int fileId) {
		this.fileId = fileId;
	}

	public void setCurrentPageId(int currentPageId) {
		this.currentPageId = currentPageId;
	}

	public void setMaxPageId(int maxPageId) {
		this.maxPageId = maxPageId;
	}
}