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AcknowledgedCounterGenerator.java
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Sat, Jun 29, 14:53

AcknowledgedCounterGenerator.java
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/**
* Copyright (c) 2015 YCSB contributors. 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. See accompanying
* LICENSE file.
*/
package com.yahoo.ycsb.generator;
import java.util.concurrent.locks.ReentrantLock;
/**
* A CounterGenerator that reports generated integers via lastInt()
* only after they have been acknowledged.
*/
public class AcknowledgedCounterGenerator extends CounterGenerator
{
/** The size of the window of pending id ack's. 2^20 = {@value} */
static final int WINDOW_SIZE = Integer.rotateLeft(1, 20);
/** The mask to use to turn an id into a slot in {@link #window}. */
private static final int WINDOW_MASK = WINDOW_SIZE - 1;
private final ReentrantLock lock;
private final boolean[] window;
private volatile int limit;
/**
* Create a counter that starts at countstart.
*/
public AcknowledgedCounterGenerator(int countstart)
{
super(countstart);
lock = new ReentrantLock();
window = new boolean[WINDOW_SIZE];
limit = countstart - 1;
}
/**
* In this generator, the highest acknowledged counter value
* (as opposed to the highest generated counter value).
*/
@Override
public Integer lastValue()
{
return limit;
}
/**
* Make a generated counter value available via lastInt().
*/
public void acknowledge(int value)
{
final int currentSlot = (value & WINDOW_MASK);
if (window[currentSlot] == true) {
throw new RuntimeException("Too many unacknowledged insertion keys.");
}
window[currentSlot] = true;
if (lock.tryLock()) {
// move a contiguous sequence from the window
// over to the "limit" variable
try {
// Only loop through the entire window at most once.
int beforeFirstSlot = (limit & WINDOW_MASK);
int index;
for (index = limit + 1; index != beforeFirstSlot; ++index) {
int slot = (index & WINDOW_MASK);
if (!window[slot]) {
break;
}
window[slot] = false;
}
limit = index - 1;
} finally {
lock.unlock();
}
}
}
}

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