J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 3 | * |
| 4 | * This code is free software; you can redistribute it and/or modify it |
| 5 | * under the terms of the GNU General Public License version 2 only, as |
| 6 | * published by the Free Software Foundation. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun in the LICENSE file that accompanied this code. |
| 9 | * |
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 13 | * version 2 for more details (a copy is included in the LICENSE file that |
| 14 | * accompanied this code). |
| 15 | * |
| 16 | * You should have received a copy of the GNU General Public License version |
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 19 | * |
| 20 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any questions. |
| 23 | */ |
| 24 | |
| 25 | /* |
| 26 | * This file is available under and governed by the GNU General Public |
| 27 | * License version 2 only, as published by the Free Software Foundation. |
| 28 | * However, the following notice accompanied the original version of this |
| 29 | * file: |
| 30 | * |
| 31 | * Written by Doug Lea with assistance from members of JCP JSR-166 |
| 32 | * Expert Group and released to the public domain, as explained at |
| 33 | * http://creativecommons.org/licenses/publicdomain |
| 34 | */ |
| 35 | |
| 36 | package java.util.concurrent.atomic; |
| 37 | import sun.misc.Unsafe; |
| 38 | import java.lang.reflect.*; |
| 39 | |
| 40 | /** |
| 41 | * A reflection-based utility that enables atomic updates to |
| 42 | * designated {@code volatile} reference fields of designated |
| 43 | * classes. This class is designed for use in atomic data structures |
| 44 | * in which several reference fields of the same node are |
| 45 | * independently subject to atomic updates. For example, a tree node |
| 46 | * might be declared as |
| 47 | * |
| 48 | * <pre> |
| 49 | * class Node { |
| 50 | * private volatile Node left, right; |
| 51 | * |
| 52 | * private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater = |
| 53 | * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left"); |
| 54 | * private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater = |
| 55 | * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right"); |
| 56 | * |
| 57 | * Node getLeft() { return left; } |
| 58 | * boolean compareAndSetLeft(Node expect, Node update) { |
| 59 | * return leftUpdater.compareAndSet(this, expect, update); |
| 60 | * } |
| 61 | * // ... and so on |
| 62 | * } |
| 63 | * </pre> |
| 64 | * |
| 65 | * <p>Note that the guarantees of the {@code compareAndSet} |
| 66 | * method in this class are weaker than in other atomic classes. |
| 67 | * Because this class cannot ensure that all uses of the field |
| 68 | * are appropriate for purposes of atomic access, it can |
| 69 | * guarantee atomicity only with respect to other invocations of |
| 70 | * {@code compareAndSet} and {@code set} on the same updater. |
| 71 | * |
| 72 | * @since 1.5 |
| 73 | * @author Doug Lea |
| 74 | * @param <T> The type of the object holding the updatable field |
| 75 | * @param <V> The type of the field |
| 76 | */ |
| 77 | public abstract class AtomicReferenceFieldUpdater<T, V> { |
| 78 | |
| 79 | /** |
| 80 | * Creates and returns an updater for objects with the given field. |
| 81 | * The Class arguments are needed to check that reflective types and |
| 82 | * generic types match. |
| 83 | * |
| 84 | * @param tclass the class of the objects holding the field. |
| 85 | * @param vclass the class of the field |
| 86 | * @param fieldName the name of the field to be updated. |
| 87 | * @return the updater |
| 88 | * @throws IllegalArgumentException if the field is not a volatile reference type. |
| 89 | * @throws RuntimeException with a nested reflection-based |
| 90 | * exception if the class does not hold field or is the wrong type. |
| 91 | */ |
| 92 | public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) { |
| 93 | return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass, |
| 94 | vclass, |
| 95 | fieldName); |
| 96 | } |
| 97 | |
| 98 | /** |
| 99 | * Protected do-nothing constructor for use by subclasses. |
| 100 | */ |
| 101 | protected AtomicReferenceFieldUpdater() { |
| 102 | } |
| 103 | |
| 104 | /** |
| 105 | * Atomically sets the field of the given object managed by this updater |
| 106 | * to the given updated value if the current value {@code ==} the |
| 107 | * expected value. This method is guaranteed to be atomic with respect to |
| 108 | * other calls to {@code compareAndSet} and {@code set}, but not |
| 109 | * necessarily with respect to other changes in the field. |
| 110 | * |
| 111 | * @param obj An object whose field to conditionally set |
| 112 | * @param expect the expected value |
| 113 | * @param update the new value |
| 114 | * @return true if successful. |
| 115 | */ |
| 116 | public abstract boolean compareAndSet(T obj, V expect, V update); |
| 117 | |
| 118 | /** |
| 119 | * Atomically sets the field of the given object managed by this updater |
| 120 | * to the given updated value if the current value {@code ==} the |
| 121 | * expected value. This method is guaranteed to be atomic with respect to |
| 122 | * other calls to {@code compareAndSet} and {@code set}, but not |
| 123 | * necessarily with respect to other changes in the field. |
| 124 | * |
| 125 | * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
| 126 | * and does not provide ordering guarantees, so is only rarely an |
| 127 | * appropriate alternative to {@code compareAndSet}. |
| 128 | * |
| 129 | * @param obj An object whose field to conditionally set |
| 130 | * @param expect the expected value |
| 131 | * @param update the new value |
| 132 | * @return true if successful. |
| 133 | */ |
| 134 | public abstract boolean weakCompareAndSet(T obj, V expect, V update); |
| 135 | |
| 136 | /** |
| 137 | * Sets the field of the given object managed by this updater to the |
| 138 | * given updated value. This operation is guaranteed to act as a volatile |
| 139 | * store with respect to subsequent invocations of {@code compareAndSet}. |
| 140 | * |
| 141 | * @param obj An object whose field to set |
| 142 | * @param newValue the new value |
| 143 | */ |
| 144 | public abstract void set(T obj, V newValue); |
| 145 | |
| 146 | /** |
| 147 | * Eventually sets the field of the given object managed by this |
| 148 | * updater to the given updated value. |
| 149 | * |
| 150 | * @param obj An object whose field to set |
| 151 | * @param newValue the new value |
| 152 | * @since 1.6 |
| 153 | */ |
| 154 | public abstract void lazySet(T obj, V newValue); |
| 155 | |
| 156 | /** |
| 157 | * Gets the current value held in the field of the given object managed |
| 158 | * by this updater. |
| 159 | * |
| 160 | * @param obj An object whose field to get |
| 161 | * @return the current value |
| 162 | */ |
| 163 | public abstract V get(T obj); |
| 164 | |
| 165 | /** |
| 166 | * Atomically sets the field of the given object managed by this updater |
| 167 | * to the given value and returns the old value. |
| 168 | * |
| 169 | * @param obj An object whose field to get and set |
| 170 | * @param newValue the new value |
| 171 | * @return the previous value |
| 172 | */ |
| 173 | public V getAndSet(T obj, V newValue) { |
| 174 | for (;;) { |
| 175 | V current = get(obj); |
| 176 | if (compareAndSet(obj, current, newValue)) |
| 177 | return current; |
| 178 | } |
| 179 | } |
| 180 | |
| 181 | private static final class AtomicReferenceFieldUpdaterImpl<T,V> |
| 182 | extends AtomicReferenceFieldUpdater<T,V> { |
| 183 | private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| 184 | private final long offset; |
| 185 | private final Class<T> tclass; |
| 186 | private final Class<V> vclass; |
| 187 | private final Class cclass; |
| 188 | |
| 189 | /* |
| 190 | * Internal type checks within all update methods contain |
| 191 | * internal inlined optimizations checking for the common |
| 192 | * cases where the class is final (in which case a simple |
| 193 | * getClass comparison suffices) or is of type Object (in |
| 194 | * which case no check is needed because all objects are |
| 195 | * instances of Object). The Object case is handled simply by |
| 196 | * setting vclass to null in constructor. The targetCheck and |
| 197 | * updateCheck methods are invoked when these faster |
| 198 | * screenings fail. |
| 199 | */ |
| 200 | |
| 201 | AtomicReferenceFieldUpdaterImpl(Class<T> tclass, |
| 202 | Class<V> vclass, |
| 203 | String fieldName) { |
| 204 | Field field = null; |
| 205 | Class fieldClass = null; |
| 206 | Class caller = null; |
| 207 | int modifiers = 0; |
| 208 | try { |
| 209 | field = tclass.getDeclaredField(fieldName); |
| 210 | caller = sun.reflect.Reflection.getCallerClass(3); |
| 211 | modifiers = field.getModifiers(); |
| 212 | sun.reflect.misc.ReflectUtil.ensureMemberAccess( |
| 213 | caller, tclass, null, modifiers); |
| 214 | sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass); |
| 215 | fieldClass = field.getType(); |
| 216 | } catch (Exception ex) { |
| 217 | throw new RuntimeException(ex); |
| 218 | } |
| 219 | |
| 220 | if (vclass != fieldClass) |
| 221 | throw new ClassCastException(); |
| 222 | |
| 223 | if (!Modifier.isVolatile(modifiers)) |
| 224 | throw new IllegalArgumentException("Must be volatile type"); |
| 225 | |
| 226 | this.cclass = (Modifier.isProtected(modifiers) && |
| 227 | caller != tclass) ? caller : null; |
| 228 | this.tclass = tclass; |
| 229 | if (vclass == Object.class) |
| 230 | this.vclass = null; |
| 231 | else |
| 232 | this.vclass = vclass; |
| 233 | offset = unsafe.objectFieldOffset(field); |
| 234 | } |
| 235 | |
| 236 | void targetCheck(T obj) { |
| 237 | if (!tclass.isInstance(obj)) |
| 238 | throw new ClassCastException(); |
| 239 | if (cclass != null) |
| 240 | ensureProtectedAccess(obj); |
| 241 | } |
| 242 | |
| 243 | void updateCheck(T obj, V update) { |
| 244 | if (!tclass.isInstance(obj) || |
| 245 | (update != null && vclass != null && !vclass.isInstance(update))) |
| 246 | throw new ClassCastException(); |
| 247 | if (cclass != null) |
| 248 | ensureProtectedAccess(obj); |
| 249 | } |
| 250 | |
| 251 | public boolean compareAndSet(T obj, V expect, V update) { |
| 252 | if (obj == null || obj.getClass() != tclass || cclass != null || |
| 253 | (update != null && vclass != null && |
| 254 | vclass != update.getClass())) |
| 255 | updateCheck(obj, update); |
| 256 | return unsafe.compareAndSwapObject(obj, offset, expect, update); |
| 257 | } |
| 258 | |
| 259 | public boolean weakCompareAndSet(T obj, V expect, V update) { |
| 260 | // same implementation as strong form for now |
| 261 | if (obj == null || obj.getClass() != tclass || cclass != null || |
| 262 | (update != null && vclass != null && |
| 263 | vclass != update.getClass())) |
| 264 | updateCheck(obj, update); |
| 265 | return unsafe.compareAndSwapObject(obj, offset, expect, update); |
| 266 | } |
| 267 | |
| 268 | public void set(T obj, V newValue) { |
| 269 | if (obj == null || obj.getClass() != tclass || cclass != null || |
| 270 | (newValue != null && vclass != null && |
| 271 | vclass != newValue.getClass())) |
| 272 | updateCheck(obj, newValue); |
| 273 | unsafe.putObjectVolatile(obj, offset, newValue); |
| 274 | } |
| 275 | |
| 276 | public void lazySet(T obj, V newValue) { |
| 277 | if (obj == null || obj.getClass() != tclass || cclass != null || |
| 278 | (newValue != null && vclass != null && |
| 279 | vclass != newValue.getClass())) |
| 280 | updateCheck(obj, newValue); |
| 281 | unsafe.putOrderedObject(obj, offset, newValue); |
| 282 | } |
| 283 | |
| 284 | public V get(T obj) { |
| 285 | if (obj == null || obj.getClass() != tclass || cclass != null) |
| 286 | targetCheck(obj); |
| 287 | return (V)unsafe.getObjectVolatile(obj, offset); |
| 288 | } |
| 289 | |
| 290 | private void ensureProtectedAccess(T obj) { |
| 291 | if (cclass.isInstance(obj)) { |
| 292 | return; |
| 293 | } |
| 294 | throw new RuntimeException ( |
| 295 | new IllegalAccessException("Class " + |
| 296 | cclass.getName() + |
| 297 | " can not access a protected member of class " + |
| 298 | tclass.getName() + |
| 299 | " using an instance of " + |
| 300 | obj.getClass().getName() |
| 301 | ) |
| 302 | ); |
| 303 | } |
| 304 | } |
| 305 | } |