| /* |
| * 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. |
| */ |
| 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; |
| } |
| } |