/
ResizableBlockingQueue.java
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/
ResizableBlockingQueue.java
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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.common.util.concurrent;
import java.util.concurrent.BlockingQueue;
/**
* Extends the {@code SizeBlockingQueue} to add the {@code adjustCapacity} method, which will adjust
* the capacity by a certain amount towards a maximum or minimum.
*/
final class ResizableBlockingQueue<E> extends SizeBlockingQueue<E> {
private volatile int capacity;
ResizableBlockingQueue(BlockingQueue<E> queue, int initialCapacity) {
super(queue, initialCapacity);
this.capacity = initialCapacity;
}
@Override
public int capacity() {
return this.capacity;
}
@Override
public int remainingCapacity() {
return Math.max(0, this.capacity());
}
/** Resize the limit for the queue, returning the new size limit */
public synchronized int adjustCapacity(int optimalCapacity, int adjustmentAmount, int minCapacity, int maxCapacity) {
assert adjustmentAmount > 0 : "adjustment amount should be a positive value";
assert optimalCapacity >= 0 : "desired capacity cannot be negative";
assert minCapacity >= 0 : "cannot have min capacity smaller than 0";
assert maxCapacity >= minCapacity : "cannot have max capacity smaller than min capacity";
if (optimalCapacity == capacity) {
// Yahtzee!
return this.capacity;
}
if (optimalCapacity > capacity + adjustmentAmount) {
// adjust up
final int newCapacity = Math.min(maxCapacity, capacity + adjustmentAmount);
this.capacity = newCapacity;
return newCapacity;
} else if (optimalCapacity < capacity - adjustmentAmount) {
// adjust down
final int newCapacity = Math.max(minCapacity, capacity - adjustmentAmount);
this.capacity = newCapacity;
return newCapacity;
} else {
return this.capacity;
}
}
}