/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.accumulo.core.file.blockfile.cache;
import java.util.LinkedList;
import java.util.PriorityQueue;
/**
* A memory-bound queue that will grow until an element brings total size >= maxSize. From then on, only entries that are sorted larger than the smallest
* current entry will be inserted/replaced.
*
* <p>
* Use this when you want to find the largest elements (according to their ordering, not their heap size) that consume as close to the specified maxSize as
* possible. Default behavior is to grow just above rather than just below specified max.
*
* <p>
* Object used in this queue must implement {@link HeapSize} as well as {@link Comparable}.
*/
public class CachedBlockQueue implements HeapSize {
private PriorityQueue<CachedBlock> queue;
private long heapSize;
private long maxSize;
/**
* @param maxSize
* the target size of elements in the queue
* @param blockSize
* expected average size of blocks
*/
public CachedBlockQueue(long maxSize, long blockSize) {
int initialSize = (int) Math.ceil(maxSize / (double) blockSize);
if (initialSize == 0)
initialSize++;
queue = new PriorityQueue<>(initialSize);
heapSize = 0;
this.maxSize = maxSize;
}
/**
* Attempt to add the specified cached block to this queue.
*
* <p>
* If the queue is smaller than the max size, or if the specified element is ordered before the smallest element in the queue, the element will be added to
* the queue. Otherwise, there is no side effect of this call.
*
* @param cb
* block to try to add to the queue
*/
public void add(CachedBlock cb) {
if (heapSize < maxSize) {
queue.add(cb);
heapSize += cb.heapSize();
} else {
CachedBlock head = queue.peek();
if (cb.compareTo(head) > 0) {
heapSize += cb.heapSize();
heapSize -= head.heapSize();
if (heapSize > maxSize) {
queue.poll();
} else {
heapSize += head.heapSize();
}
queue.add(cb);
}
}
}
/**
* Get a sorted List of all elements in this queue, in descending order.
*
* @return list of cached elements in descending order
*/
public CachedBlock[] get() {
LinkedList<CachedBlock> blocks = new LinkedList<>();
while (!queue.isEmpty()) {
blocks.addFirst(queue.poll());
}
return blocks.toArray(new CachedBlock[blocks.size()]);
}
/**
* Get a sorted List of all elements in this queue, in descending order.
*
* @return list of cached elements in descending order
*/
public LinkedList<CachedBlock> getList() {
LinkedList<CachedBlock> blocks = new LinkedList<>();
while (!queue.isEmpty()) {
blocks.addFirst(queue.poll());
}
return blocks;
}
/**
* Total size of all elements in this queue.
*
* @return size of all elements currently in queue, in bytes
*/
@Override
public long heapSize() {
return heapSize;
}
}