106 lines
2.8 KiB
Java
106 lines
2.8 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.tomcat.util.collections;
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/**
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* This is intended as a (mostly) GC-free alternative to
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* {@link java.util.concurrent.ConcurrentLinkedQueue} when the requirement is to
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* create an unbounded queue with no requirement to shrink the queue. The aim is
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* to provide the bare minimum of required functionality as quickly as possible
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* with minimum garbage.
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*
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* @param <T> The type of object managed by this queue
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*/
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public class SynchronizedQueue<T> {
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public static final int DEFAULT_SIZE = 128;
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private Object[] queue;
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private int size;
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private int insert = 0;
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private int remove = 0;
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public SynchronizedQueue() {
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this(DEFAULT_SIZE);
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}
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public SynchronizedQueue(int initialSize) {
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queue = new Object[initialSize];
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size = initialSize;
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}
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public synchronized boolean offer(T t) {
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queue[insert++] = t;
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// Wrap
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if (insert == size) {
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insert = 0;
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}
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if (insert == remove) {
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expand();
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}
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return true;
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}
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public synchronized T poll() {
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if (insert == remove) {
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// empty
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return null;
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}
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@SuppressWarnings("unchecked")
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T result = (T) queue[remove];
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queue[remove] = null;
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remove++;
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// Wrap
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if (remove == size) {
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remove = 0;
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}
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return result;
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}
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private void expand() {
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int newSize = size * 2;
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Object[] newQueue = new Object[newSize];
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System.arraycopy(queue, insert, newQueue, 0, size - insert);
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System.arraycopy(queue, 0, newQueue, size - insert, insert);
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insert = size;
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remove = 0;
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queue = newQueue;
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size = newSize;
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}
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public synchronized int size() {
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int result = insert - remove;
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if (result < 0) {
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result += size;
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}
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return result;
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}
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public synchronized void clear() {
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queue = new Object[size];
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insert = 0;
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remove = 0;
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}
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}
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