| 1 | /* ============================================================= |
| 2 | * SmallSQL : a free Java DBMS library for the Java(tm) platform |
| 3 | * ============================================================= |
| 4 | * |
| 5 | * (C) Copyright 2004-2006, by Volker Berlin. |
| 6 | * |
| 7 | * Project Info: http://www.smallsql.de/ |
| 8 | * |
| 9 | * This library is free software; you can redistribute it and/or modify it |
| 10 | * under the terms of the GNU Lesser General Public License as published by |
| 11 | * the Free Software Foundation; either version 2.1 of the License, or |
| 12 | * (at your option) any later version. |
| 13 | * |
| 14 | * This library is distributed in the hope that it will be useful, but |
| 15 | * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 16 | * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
| 17 | * License for more details. |
| 18 | * |
| 19 | * You should have received a copy of the GNU Lesser General Public |
| 20 | * License along with this library; if not, write to the Free Software |
| 21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, |
| 22 | * USA. |
| 23 | * |
| 24 | * [Java is a trademark or registered trademark of Sun Microsystems, Inc. |
| 25 | * in the United States and other countries.] |
| 26 | * |
| 27 | * --------------- |
| 28 | * StorePageMap.java |
| 29 | * --------------- |
| 30 | * Author: Volker Berlin |
| 31 | * |
| 32 | * Created on 13.08.2004 |
| 33 | */ |
| 34 | package smallsql.database; |
| 35 | |
| 36 | /** |
| 37 | * @author Volker Berlin |
| 38 | */ |
| 39 | class StorePageMap { |
| 40 | |
| 41 | |
| 42 | |
| 43 | /** |
| 44 | * The table, resized as necessary. Length MUST Always be a power of two. |
| 45 | */ |
| 46 | private Entry[] table; |
| 47 | |
| 48 | /** |
| 49 | * The number of key-value mappings contained in this identity hash map. |
| 50 | */ |
| 51 | private int size; |
| 52 | |
| 53 | /** |
| 54 | * The next size value at which to resize (capacity * load factor). |
| 55 | * @serial |
| 56 | */ |
| 57 | private int threshold; |
| 58 | |
| 59 | |
| 60 | |
| 61 | |
| 62 | |
| 63 | /** |
| 64 | * Constructs an empty <tt>HashMap</tt> with the default initial capacity |
| 65 | * (16) and the default load factor (0.75). |
| 66 | */ |
| 67 | StorePageMap() { |
| 68 | threshold = 12; |
| 69 | table = new Entry[17]; |
| 70 | } |
| 71 | |
| 72 | |
| 73 | |
| 74 | |
| 75 | |
| 76 | |
| 77 | /** |
| 78 | * Returns the number of key-value mappings in this map. |
| 79 | * |
| 80 | * @return the number of key-value mappings in this map. |
| 81 | */ |
| 82 | final int size() { |
| 83 | return size; |
| 84 | } |
| 85 | |
| 86 | /** |
| 87 | * Returns <tt>true</tt> if this map contains no key-value mappings. |
| 88 | * |
| 89 | * @return <tt>true</tt> if this map contains no key-value mappings. |
| 90 | */ |
| 91 | final boolean isEmpty() { |
| 92 | return size == 0; |
| 93 | } |
| 94 | |
| 95 | /** |
| 96 | * Returns the first StorePage for the given key. |
| 97 | */ |
| 98 | final TableStorePage get(long key) { |
| 99 | int i = (int)(key % table.length); |
| 100 | Entry e = table[i]; |
| 101 | while (true) { |
| 102 | if (e == null) |
| 103 | return null; |
| 104 | if (e.key == key) |
| 105 | return e.value; |
| 106 | e = e.next; |
| 107 | } |
| 108 | } |
| 109 | |
| 110 | /** |
| 111 | * Returns <tt>true</tt> if this map contains a StorePage for the |
| 112 | * specified key. |
| 113 | * |
| 114 | */ |
| 115 | final boolean containsKey(long key) { |
| 116 | return (get(key) != null); |
| 117 | } |
| 118 | |
| 119 | |
| 120 | /** |
| 121 | * Add the StorePage with the key. Multiple StorePage for the same key are valid. |
| 122 | * The cause are multiple changes in one transaction. With SavePoints a rollback to a older |
| 123 | * StorePage is valid.<p> |
| 124 | * The latest StorePage is placed at first pos. |
| 125 | */ |
| 126 | final TableStorePage add(long key, TableStorePage value) { |
| 127 | int i = (int)(key % table.length); |
| 128 | |
| 129 | table[i] = new Entry(key, value, table[i]); |
| 130 | if (size++ >= threshold) |
| 131 | resize(2 * table.length); |
| 132 | return null; |
| 133 | } |
| 134 | |
| 135 | |
| 136 | /** |
| 137 | * Rehashes the contents of this map into a new array with a |
| 138 | * larger capacity. This method is called automatically when the |
| 139 | * number of keys in this map reaches its threshold. |
| 140 | * |
| 141 | * If current capacity is MAXIMUM_CAPACITY, this method does not |
| 142 | * resize the map, but but sets threshold to Integer.MAX_VALUE. |
| 143 | * This has the effect of preventing future calls. |
| 144 | * |
| 145 | * @param newCapacity the new capacity, MUST be a power of two; |
| 146 | * must be greater than current capacity unless current |
| 147 | * capacity is MAXIMUM_CAPACITY (in which case value |
| 148 | * is irrelevant). |
| 149 | */ |
| 150 | final private void resize(int newCapacity) { |
| 151 | |
| 152 | Entry[] newTable = new Entry[newCapacity]; |
| 153 | transfer(newTable); |
| 154 | table = newTable; |
| 155 | threshold = (int)(newCapacity * 0.75f); |
| 156 | } |
| 157 | |
| 158 | /** |
| 159 | * Transfer all entries from current table to newTable. |
| 160 | */ |
| 161 | final private void transfer(Entry[] newTable) { |
| 162 | Entry[] src = table; |
| 163 | int newCapacity = newTable.length; |
| 164 | for (int j = 0; j < src.length; j++) { |
| 165 | Entry e = src[j]; |
| 166 | if (e != null) { |
| 167 | src[j] = null; |
| 168 | do { |
| 169 | Entry next = e.next; |
| 170 | e.next = null; |
| 171 | int i = (int)(e.key % newCapacity); |
| 172 | //The order for StorePages with the same key must not change |
| 173 | //that we need to find the end of the link list. This is different to a typical HashTable |
| 174 | if(newTable[i] == null){ |
| 175 | newTable[i] = e; |
| 176 | }else{ |
| 177 | Entry entry = newTable[i]; |
| 178 | while(entry.next != null) entry = entry.next; |
| 179 | entry.next = e; |
| 180 | } |
| 181 | e = next; |
| 182 | } while (e != null); |
| 183 | } |
| 184 | } |
| 185 | } |
| 186 | |
| 187 | |
| 188 | /** |
| 189 | * Removes the mapping for this key from this map if present. |
| 190 | * |
| 191 | * @param key key whose mapping is to be removed from the map. |
| 192 | * @return previous value associated with specified key, or <tt>null</tt> |
| 193 | * if there was no mapping for key. A <tt>null</tt> return can |
| 194 | * also indicate that the map previously associated <tt>null</tt> |
| 195 | * with the specified key. |
| 196 | */ |
| 197 | final TableStorePage remove(long key) { |
| 198 | int i = (int)(key % table.length); |
| 199 | Entry prev = table[i]; |
| 200 | Entry e = prev; |
| 201 | |
| 202 | while (e != null) { |
| 203 | Entry next = e.next; |
| 204 | if (e.key == key) { |
| 205 | size--; |
| 206 | if (prev == e) |
| 207 | table[i] = next; |
| 208 | else |
| 209 | prev.next = next; |
| 210 | return e.value; |
| 211 | } |
| 212 | prev = e; |
| 213 | e = next; |
| 214 | } |
| 215 | return null; |
| 216 | } |
| 217 | |
| 218 | |
| 219 | /** |
| 220 | * Removes all mappings from this map. |
| 221 | */ |
| 222 | final void clear() { |
| 223 | Entry tab[] = table; |
| 224 | for (int i = 0; i < tab.length; i++) |
| 225 | tab[i] = null; |
| 226 | size = 0; |
| 227 | } |
| 228 | |
| 229 | /** |
| 230 | * Returns <tt>true</tt> if this map maps one or more keys to the |
| 231 | * specified value. |
| 232 | * |
| 233 | * @param value value whose presence in this map is to be tested. |
| 234 | * @return <tt>true</tt> if this map maps one or more keys to the |
| 235 | * specified value. |
| 236 | */ |
| 237 | final boolean containsValue(TableStorePage value) { |
| 238 | Entry tab[] = table; |
| 239 | for (int i = 0; i < tab.length ; i++) |
| 240 | for (Entry e = tab[i] ; e != null ; e = e.next) |
| 241 | if (value.equals(e.value)) |
| 242 | return true; |
| 243 | return false; |
| 244 | } |
| 245 | |
| 246 | |
| 247 | |
| 248 | static class Entry{ |
| 249 | final long key; |
| 250 | final TableStorePage value; |
| 251 | Entry next; |
| 252 | |
| 253 | /** |
| 254 | * Create new entry. |
| 255 | */ |
| 256 | Entry(long k, TableStorePage v, Entry n) { |
| 257 | value = v; |
| 258 | next = n; |
| 259 | key = k; |
| 260 | } |
| 261 | |
| 262 | |
| 263 | } |
| 264 | |
| 265 | |
| 266 | } |