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/*
* Copyright 2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* 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 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 com.amazon.carbonado.cursor;
import java.util.ArrayDeque;
import java.util.NoSuchElementException;
import java.util.Queue;
import com.amazon.carbonado.Cursor;
import com.amazon.carbonado.FetchException;
/**
* Cursor implementation which fetches records in advance, in order to release locks.
*
* @author Brian S O'Neill
*/
public class FetchAheadCursor<S> extends AbstractCursor<S> {
private final Cursor<S> mSource;
private final int mFetchAhead;
private final Queue<Object> mQueue;
/**
* @param fetchAhead how much to fetch ahead from source
*/
public FetchAheadCursor(Cursor<S> source, int fetchAhead) {
mSource = source;
mFetchAhead = fetchAhead;
mQueue = new ArrayDeque<Object>(fetchAhead + 1);
}
public void close() throws FetchException {
mQueue.clear();
mSource.close();
}
public boolean hasNext() throws FetchException {
while (mQueue.size() <= mFetchAhead && mSource.hasNext()) {
try {
mQueue.add(mSource.next());
} catch (FetchException e) {
mQueue.add(e);
}
}
return !mQueue.isEmpty();
}
public S next() throws FetchException {
if (!hasNext()) {
throw new NoSuchElementException();
}
Object next = mQueue.remove();
if (next instanceof FetchException) {
throw (FetchException) next;
}
return (S) next;
}
}
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