001 package org.apache.fulcrum.pool; 002 003 004 /* 005 * Licensed to the Apache Software Foundation (ASF) under one 006 * or more contributor license agreements. See the NOTICE file 007 * distributed with this work for additional information 008 * regarding copyright ownership. The ASF licenses this file 009 * to you under the Apache License, Version 2.0 (the 010 * "License"); you may not use this file except in compliance 011 * with the License. You may obtain a copy of the License at 012 * 013 * http://www.apache.org/licenses/LICENSE-2.0 014 * 015 * Unless required by applicable law or agreed to in writing, 016 * software distributed under the License is distributed on an 017 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 018 * KIND, either express or implied. See the License for the 019 * specific language governing permissions and limitations 020 * under the License. 021 */ 022 023 024 /** 025 * Efficient array-based bounded buffer class. 026 * Adapted from CPJ, chapter 8, which describes design. 027 * Originally written by Doug Lea and released into the public domain. 028 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p> 029 * 030 * @author <a href="mailto:ilkka.priha@simsoft.fi">Ilkka Priha</a> 031 * @version $Id: BoundedBuffer.java 535465 2007-05-05 06:58:06Z tv $ 032 */ 033 public class BoundedBuffer 034 { 035 /** 036 * The default capacity. 037 */ 038 public static final int DEFAULT_CAPACITY = 1024; 039 040 protected final Object[] array_; // the elements 041 042 protected int takePtr_ = 0; // circular indices 043 protected int putPtr_ = 0; 044 045 protected int usedSlots_ = 0; // length 046 protected int emptySlots_; // capacity - length 047 048 /** 049 * Creates a buffer with the given capacity. 050 * 051 * @param capacity the capacity. 052 * @throws IllegalArgumentException if capacity less or equal to zero. 053 */ 054 public BoundedBuffer(int capacity) 055 throws IllegalArgumentException 056 { 057 if (capacity <= 0) 058 throw new IllegalArgumentException(); 059 060 array_ = new Object[capacity]; 061 emptySlots_ = capacity; 062 } 063 064 /** 065 * Creates a buffer with the default capacity 066 */ 067 public BoundedBuffer() 068 { 069 this(DEFAULT_CAPACITY); 070 } 071 072 /** 073 * Returns the number of elements in the buffer. 074 * This is only a snapshot value, that may change 075 * immediately after returning. 076 * 077 * @return the size. 078 */ 079 public synchronized int size() 080 { 081 return usedSlots_; 082 } 083 084 /** 085 * Returns the capacity of the buffer. 086 * 087 * @return the capacity. 088 */ 089 public int capacity() 090 { 091 return array_.length; 092 } 093 094 /** 095 * Peeks, but does not remove the top item from the buffer. 096 * 097 * @return the object or null. 098 */ 099 public synchronized Object peek() 100 { 101 if (usedSlots_ > 0) 102 return array_[takePtr_]; 103 else 104 return null; 105 } 106 107 /** 108 * Puts an item in the buffer only if there is capacity available. 109 * 110 * @param item the item to be inserted. 111 * @return true if accepted, else false. 112 */ 113 public synchronized boolean offer(Object x) 114 { 115 if (x == null) 116 throw new IllegalArgumentException(); 117 118 if (emptySlots_ > 0) 119 { 120 --emptySlots_; 121 array_[putPtr_] = x; 122 if (++putPtr_ >= array_.length) 123 putPtr_ = 0; 124 usedSlots_++; 125 return true; 126 } 127 else 128 return false; 129 } 130 131 /** 132 * Polls and removes the top item from the buffer if one is available. 133 * 134 * @return the oldest item from the buffer, or null if the buffer is empty. 135 */ 136 public synchronized Object poll() 137 { 138 if (usedSlots_ > 0) 139 { 140 --usedSlots_; 141 Object old = array_[takePtr_]; 142 array_[takePtr_] = null; 143 if (++takePtr_ >= array_.length) 144 takePtr_ = 0; 145 emptySlots_++; 146 return old; 147 } 148 else 149 return null; 150 } 151 }