/*
* 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.tomcat.util.collections;
/**
* This is intended as a (mostly) GC-free alternative to {@link java.util.concurrent.ConcurrentLinkedQueue} when the
* requirement is to create an unbounded queue with no requirement to shrink the queue. The aim is to provide the bare
* minimum of required functionality as quickly as possible with minimum garbage.
*
* @param <T> The type of object managed by this queue
*/
public class SynchronizedQueue<T> {
public static final int DEFAULT_SIZE = 128;
private Object[] queue;
private int size;
private int insert = 0;
private int remove = 0;
public SynchronizedQueue() {
this(DEFAULT_SIZE);
}
public SynchronizedQueue(int initialSize) {
queue = new Object[initialSize];
size = initialSize;
}
public synchronized boolean offer(T t) {
queue[insert++] = t;
// Wrap
if (insert == size) {
insert = 0;
}
if (insert == remove) {
expand();
}
return true;
}
public synchronized T poll() {
if (insert == remove) {
// empty
return null;
}
@SuppressWarnings("unchecked")
T result = (T) queue[remove];
queue[remove] = null;
remove++;
// Wrap
if (remove == size) {
remove = 0;
}
return result;
}
private void expand() {
int newSize = size * 2;
Object[] newQueue = new Object[newSize];
System.arraycopy(queue, insert, newQueue, 0, size - insert);
System.arraycopy(queue, 0, newQueue, size - insert, insert);
insert = size;
remove = 0;
queue = newQueue;
size = newSize;
}
public synchronized int size() {
int result = insert - remove;
if (result < 0) {
result += size;
}
return result;
}
public synchronized void clear() {
queue = new Object[size];
insert = 0;
remove = 0;
}
}