| /* |
| * 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 a pool of re-usable objects with no requirement to shrink the pool. |
| * The aim is to provide the bare minimum of required functionality as quickly |
| * as possible with minimum garbage. |
| */ |
| public class SynchronizedStack<T> { |
| |
| public static final int DEFAULT_SIZE = 128; |
| private static final int DEFAULT_LIMIT = -1; |
| |
| private int size; |
| private final int limit; |
| |
| /* |
| * Points to the next available object in the stack |
| */ |
| private int index = -1; |
| |
| private Object[] stack; |
| |
| |
| public SynchronizedStack() { |
| this(DEFAULT_SIZE, DEFAULT_LIMIT); |
| } |
| |
| public SynchronizedStack(int size, int limit) { |
| this.size = size; |
| this.limit = limit; |
| stack = new Object[size]; |
| } |
| |
| |
| public synchronized boolean push(T obj) { |
| index++; |
| if (index == size) { |
| if (limit == -1 || size < limit) { |
| expand(); |
| } else { |
| index--; |
| return false; |
| } |
| } |
| stack[index] = obj; |
| return true; |
| } |
| |
| @SuppressWarnings("unchecked") |
| public synchronized T pop() { |
| if (index == -1) { |
| return null; |
| } |
| T result = (T) stack[index]; |
| stack[index--] = null; |
| return result; |
| } |
| |
| public synchronized void clear() { |
| if (index > -1) { |
| for (int i = 0; i < index + 1; i++) { |
| stack[i] = null; |
| } |
| } |
| index = -1; |
| } |
| |
| private void expand() { |
| int newSize = size * 2; |
| if (limit != -1 && newSize > limit) { |
| newSize = limit; |
| } |
| Object[] newStack = new Object[newSize]; |
| System.arraycopy(stack, 0, newStack, 0, size); |
| // This is the only point where garbage is created by throwing away the |
| // old array. Note it is only the array, not the contents, that becomes |
| // garbage. |
| stack = newStack; |
| size = newSize; |
| } |
| } |