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/*
* Copyright 2006-2012 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.NoSuchElementException;
import com.amazon.carbonado.Cursor;
import com.amazon.carbonado.FetchException;
import com.amazon.carbonado.FetchInterruptedException;
import com.amazon.carbonado.util.Throttle;
/**
* Wraps another cursor and fetches results at a reduced speed.
*
* @author Brian S O'Neill
*/
public class ThrottledCursor<S> extends AbstractCursor<S> {
private static final int WINDOW_SIZE = 10;
private static final int SLEEP_PRECISION_MILLIS = 50;
private final Cursor<S> mCursor;
private final Throttle mThrottle;
private final double mDesiredSpeed;
/**
* @param cursor cursor to wrap
* @param throttle 1.0 = fetch at full speed, 0.5 = fetch at half speed,
* 0.1 = fetch at one tenth speed, etc.
*/
public ThrottledCursor(Cursor<S> cursor, double throttle) {
mCursor = cursor;
if (throttle < 1.0) {
if (throttle < 0.0) {
throttle = 0.0;
}
mThrottle = new Throttle(WINDOW_SIZE);
mDesiredSpeed = throttle;
} else {
mThrottle = null;
mDesiredSpeed = 1.0;
}
}
public void close() throws FetchException {
mCursor.close();
}
public boolean hasNext() throws FetchException {
try {
return mCursor.hasNext();
} catch (NoSuchElementException e) {
return false;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
public S next() throws FetchException {
try {
throttle();
return mCursor.next();
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
@Override
public int skipNext(int amount) throws FetchException {
if (amount <= 0) {
if (amount < 0) {
throw new IllegalArgumentException("Cannot skip negative amount: " + amount);
}
return 0;
}
try {
int count = 0;
while (--amount >= 0) {
throttle();
if (skipNext(1) <= 0) {
break;
}
count++;
}
return count;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
private void throttle() throws FetchInterruptedException {
if (mThrottle != null) {
try {
mThrottle.throttle(mDesiredSpeed, SLEEP_PRECISION_MILLIS);
} catch (InterruptedException e) {
throw new FetchInterruptedException(e);
}
}
}
}
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