| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.store.access.sort.NodeAllocator |
| 4 | |
| 5 | Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.impl.store.access.sort; |
| 22 | |
| 23 | /** |
| 24 | |
| 25 | NodeAllocator manages an array of nodes which can be reused. |
| 26 | |
| 27 | **/ |
| 28 | |
| 29 | final class NodeAllocator |
| 30 | { |
| 31 | private static final int DEFAULT_INIT_SIZE = 128; |
| 32 | private static final int GROWTH_MULTIPLIER = 2; |
| 33 | private static final int DEFAULT_MAX_SIZE = 1024; |
| 34 | |
| 35 | private Node array[]; |
| 36 | private int maxSize; |
| 37 | private int nAllocated; |
| 38 | private Node freeList = null; |
| 39 | |
| 40 | /** |
| 41 | Construct an empty allocator. The caller must call |
| 42 | init() before using it. |
| 43 | **/ |
| 44 | public NodeAllocator() |
| 45 | { |
| 46 | array = null; |
| 47 | nAllocated = 0; |
| 48 | maxSize = 0; |
| 49 | } |
| 50 | |
| 51 | public Node newNode() |
| 52 | { |
| 53 | // Caller forgot to init? |
| 54 | if (array == null) |
| 55 | { |
| 56 | if (init() == false) |
| 57 | return null; |
| 58 | } |
| 59 | |
| 60 | if (freeList != null) |
| 61 | { |
| 62 | Node n = freeList; |
| 63 | freeList = n.rightLink; |
| 64 | n.rightLink = null; |
| 65 | return n; |
| 66 | } |
| 67 | |
| 68 | // Do we need to try reallocating the array? |
| 69 | if (nAllocated == array.length) |
| 70 | { |
| 71 | // If the array is already the maximum size, then |
| 72 | // tell the caller that there are no more nodes |
| 73 | // available. |
| 74 | if (array.length >= maxSize) |
| 75 | return null; |
| 76 | |
| 77 | // Attempt to allocate a new array. If the allocation |
| 78 | // fails, tell the caller that there are no more |
| 79 | // nodes available. |
| 80 | Node[] newArray = new Node[array.length * GROWTH_MULTIPLIER]; |
| 81 | if (newArray == null) |
| 82 | return null; |
| 83 | |
| 84 | // The new array was successfully allocated. Copy the |
| 85 | // nodes from the original array into it, and make the |
| 86 | // new array the allocator's array. |
| 87 | System.arraycopy(array, 0, newArray, 0, array.length); |
| 88 | array = newArray; |
| 89 | } |
| 90 | |
| 91 | // If this slot in the array hasn't had a node |
| 92 | // allocated for it yet, do so now. |
| 93 | if (array[nAllocated] == null) |
| 94 | array[nAllocated] = new Node(nAllocated); |
| 95 | |
| 96 | // Return the node and increase the allocated count. |
| 97 | return array[nAllocated++]; |
| 98 | } |
| 99 | |
| 100 | /** |
| 101 | Return a node to the allocator. |
| 102 | **/ |
| 103 | public void freeNode(Node n) |
| 104 | { |
| 105 | n.reset(); |
| 106 | n.rightLink = freeList; |
| 107 | freeList = n; |
| 108 | } |
| 109 | |
| 110 | /** |
| 111 | Initialize the allocator with default values for |
| 112 | initial and maximum size. Returns false if sufficient |
| 113 | memory could not be allocated. |
| 114 | **/ |
| 115 | public boolean init() |
| 116 | { |
| 117 | return init(DEFAULT_INIT_SIZE, DEFAULT_MAX_SIZE); |
| 118 | } |
| 119 | |
| 120 | /** |
| 121 | Initialize the allocator with default values for |
| 122 | initial size and the provided maximum size. |
| 123 | Returns false if sufficient memory could not be allocated. |
| 124 | **/ |
| 125 | public boolean init(int maxSize) |
| 126 | { |
| 127 | return init(DEFAULT_INIT_SIZE, maxSize); |
| 128 | } |
| 129 | |
| 130 | /** |
| 131 | Initialize the allocator with the given initial and |
| 132 | maximum sizes. This method does not check, but assumes |
| 133 | that the value of initSize is less than the value of |
| 134 | maxSize, and that they are both powers of two. Returns |
| 135 | false if sufficient memory could not be allocated. |
| 136 | **/ |
| 137 | public boolean init(int initSize, int maxSize) |
| 138 | { |
| 139 | this.maxSize = maxSize; |
| 140 | if (maxSize < initSize) |
| 141 | initSize = maxSize; |
| 142 | array = new Node[initSize]; |
| 143 | if (array == null) |
| 144 | return false; |
| 145 | nAllocated = 0; |
| 146 | return true; |
| 147 | } |
| 148 | |
| 149 | /** |
| 150 | Expand the node allocator's capacity by certain percent. |
| 151 | **/ |
| 152 | public void grow(int percent) |
| 153 | { |
| 154 | if (percent > 0) // cannot shrink |
| 155 | maxSize = maxSize * (100+percent)/100; |
| 156 | } |
| 157 | |
| 158 | /** |
| 159 | Clear all nodes that this allocator has allocated. |
| 160 | The allocator must already have been initialized. |
| 161 | **/ |
| 162 | public void reset() |
| 163 | { |
| 164 | if (array == null) |
| 165 | return; |
| 166 | for (int i = 0; i < nAllocated; i++) |
| 167 | array[i].reset(); |
| 168 | nAllocated = 0; |
| 169 | freeList = null; |
| 170 | } |
| 171 | |
| 172 | public void close() |
| 173 | { |
| 174 | array = null; |
| 175 | nAllocated = 0; |
| 176 | maxSize = 0; |
| 177 | freeList = null; |
| 178 | } |
| 179 | |
| 180 | public int capacity() |
| 181 | { |
| 182 | return maxSize; |
| 183 | } |
| 184 | } |