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| 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. Oracle designates this | |
| 7 | + * particular file as subject to the "Classpath" exception as provided | |
| 8 | + * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 21 | + * or visit www.oracle.com if you need additional information or have any | |
| 22 | + * 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/publicdomain/zero/1.0/ | |
| 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> {@code | |
| 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 | + * }}</pre> | |
| 63 | + * | |
| 64 | + * <p>Note that the guarantees of the {@code compareAndSet} | |
| 65 | + * method in this class are weaker than in other atomic classes. | |
| 66 | + * Because this class cannot ensure that all uses of the field | |
| 67 | + * are appropriate for purposes of atomic access, it can | |
| 68 | + * guarantee atomicity only with respect to other invocations of | |
| 69 | + * {@code compareAndSet} and {@code set} on the same updater. | |
| 70 | + * | |
| 71 | + * @since 1.5 | |
| 72 | + * @author Doug Lea | |
| 73 | + * @param <T> The type of the object holding the updatable field | |
| 74 | + * @param <V> The type of the field | |
| 75 | + */ | |
| 76 | +public abstract class AtomicReferenceFieldUpdater<T, V> { | |
| 77 | + | |
| 78 | + /** | |
| 79 | + * Creates and returns an updater for objects with the given field. | |
| 80 | + * The Class arguments are needed to check that reflective types and | |
| 81 | + * generic types match. | |
| 82 | + * | |
| 83 | + * @param tclass the class of the objects holding the field. | |
| 84 | + * @param vclass the class of the field | |
| 85 | + * @param fieldName the name of the field to be updated. | |
| 86 | + * @return the updater | |
| 87 | + * @throws IllegalArgumentException if the field is not a volatile reference type. | |
| 88 | + * @throws RuntimeException with a nested reflection-based | |
| 89 | + * exception if the class does not hold field or is the wrong type. | |
| 90 | + */ | |
| 91 | + public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) { | |
| 92 | + return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass, | |
| 93 | + vclass, | |
| 94 | + fieldName); | |
| 95 | + } | |
| 96 | + | |
| 97 | + /** | |
| 98 | + * Protected do-nothing constructor for use by subclasses. | |
| 99 | + */ | |
| 100 | + protected AtomicReferenceFieldUpdater() { | |
| 101 | + } | |
| 102 | + | |
| 103 | + /** | |
| 104 | + * Atomically sets the field of the given object managed by this updater | |
| 105 | + * to the given updated value if the current value {@code ==} the | |
| 106 | + * expected value. This method is guaranteed to be atomic with respect to | |
| 107 | + * other calls to {@code compareAndSet} and {@code set}, but not | |
| 108 | + * necessarily with respect to other changes in the field. | |
| 109 | + * | |
| 110 | + * @param obj An object whose field to conditionally set | |
| 111 | + * @param expect the expected value | |
| 112 | + * @param update the new value | |
| 113 | + * @return true if successful. | |
| 114 | + */ | |
| 115 | + public abstract boolean compareAndSet(T obj, V expect, V update); | |
| 116 | + | |
| 117 | + /** | |
| 118 | + * Atomically sets the field of the given object managed by this updater | |
| 119 | + * to the given updated value if the current value {@code ==} the | |
| 120 | + * expected value. This method is guaranteed to be atomic with respect to | |
| 121 | + * other calls to {@code compareAndSet} and {@code set}, but not | |
| 122 | + * necessarily with respect to other changes in the field. | |
| 123 | + * | |
| 124 | + * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> | |
| 125 | + * and does not provide ordering guarantees, so is only rarely an | |
| 126 | + * appropriate alternative to {@code compareAndSet}. | |
| 127 | + * | |
| 128 | + * @param obj An object whose field to conditionally set | |
| 129 | + * @param expect the expected value | |
| 130 | + * @param update the new value | |
| 131 | + * @return true if successful. | |
| 132 | + */ | |
| 133 | + public abstract boolean weakCompareAndSet(T obj, V expect, V update); | |
| 134 | + | |
| 135 | + /** | |
| 136 | + * Sets the field of the given object managed by this updater to the | |
| 137 | + * given updated value. This operation is guaranteed to act as a volatile | |
| 138 | + * store with respect to subsequent invocations of {@code compareAndSet}. | |
| 139 | + * | |
| 140 | + * @param obj An object whose field to set | |
| 141 | + * @param newValue the new value | |
| 142 | + */ | |
| 143 | + public abstract void set(T obj, V newValue); | |
| 144 | + | |
| 145 | + /** | |
| 146 | + * Eventually sets the field of the given object managed by this | |
| 147 | + * updater to the given updated value. | |
| 148 | + * | |
| 149 | + * @param obj An object whose field to set | |
| 150 | + * @param newValue the new value | |
| 151 | + * @since 1.6 | |
| 152 | + */ | |
| 153 | + public abstract void lazySet(T obj, V newValue); | |
| 154 | + | |
| 155 | + /** | |
| 156 | + * Gets the current value held in the field of the given object managed | |
| 157 | + * by this updater. | |
| 158 | + * | |
| 159 | + * @param obj An object whose field to get | |
| 160 | + * @return the current value | |
| 161 | + */ | |
| 162 | + public abstract V get(T obj); | |
| 163 | + | |
| 164 | + /** | |
| 165 | + * Atomically sets the field of the given object managed by this updater | |
| 166 | + * to the given value and returns the old value. | |
| 167 | + * | |
| 168 | + * @param obj An object whose field to get and set | |
| 169 | + * @param newValue the new value | |
| 170 | + * @return the previous value | |
| 171 | + */ | |
| 172 | + public V getAndSet(T obj, V newValue) { | |
| 173 | + for (;;) { | |
| 174 | + V current = get(obj); | |
| 175 | + if (compareAndSet(obj, current, newValue)) | |
| 176 | + return current; | |
| 177 | + } | |
| 178 | + } | |
| 179 | + | |
| 180 | + private static final class AtomicReferenceFieldUpdaterImpl<T,V> | |
| 181 | + extends AtomicReferenceFieldUpdater<T,V> { | |
| 182 | + private static final Unsafe unsafe = Unsafe.getUnsafe(); | |
| 183 | + private final long offset; | |
| 184 | + private final Class<T> tclass; | |
| 185 | + private final Class<V> vclass; | |
| 186 | + private final Class cclass; | |
| 187 | + | |
| 188 | + /* | |
| 189 | + * Internal type checks within all update methods contain | |
| 190 | + * internal inlined optimizations checking for the common | |
| 191 | + * cases where the class is final (in which case a simple | |
| 192 | + * getClass comparison suffices) or is of type Object (in | |
| 193 | + * which case no check is needed because all objects are | |
| 194 | + * instances of Object). The Object case is handled simply by | |
| 195 | + * setting vclass to null in constructor. The targetCheck and | |
| 196 | + * updateCheck methods are invoked when these faster | |
| 197 | + * screenings fail. | |
| 198 | + */ | |
| 199 | + | |
| 200 | + AtomicReferenceFieldUpdaterImpl(Class<T> tclass, | |
| 201 | + Class<V> vclass, | |
| 202 | + String fieldName) { | |
| 203 | + Field field = null; | |
| 204 | + Class fieldClass = null; | |
| 205 | + Class caller = null; | |
| 206 | + int modifiers = 0; | |
| 207 | + try { | |
| 208 | + field = tclass.getDeclaredField(fieldName); | |
| 209 | + caller = sun.reflect.Reflection.getCallerClass(3); | |
| 210 | + modifiers = field.getModifiers(); | |
| 211 | + sun.reflect.misc.ReflectUtil.ensureMemberAccess( | |
| 212 | + caller, tclass, null, modifiers); | |
| 213 | + sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass); | |
| 214 | + fieldClass = field.getType(); | |
| 215 | + } catch (Exception ex) { | |
| 216 | + throw new RuntimeException(ex); | |
| 217 | + } | |
| 218 | + | |
| 219 | + if (vclass != fieldClass) | |
| 220 | + throw new ClassCastException(); | |
| 221 | + | |
| 222 | + if (!Modifier.isVolatile(modifiers)) | |
| 223 | + throw new IllegalArgumentException("Must be volatile type"); | |
| 224 | + | |
| 225 | + this.cclass = (Modifier.isProtected(modifiers) && | |
| 226 | + caller != tclass) ? caller : null; | |
| 227 | + this.tclass = tclass; | |
| 228 | + if (vclass == Object.class) | |
| 229 | + this.vclass = null; | |
| 230 | + else | |
| 231 | + this.vclass = vclass; | |
| 232 | + offset = unsafe.objectFieldOffset(field); | |
| 233 | + } | |
| 234 | + | |
| 235 | + void targetCheck(T obj) { | |
| 236 | + if (!tclass.isInstance(obj)) | |
| 237 | + throw new ClassCastException(); | |
| 238 | + if (cclass != null) | |
| 239 | + ensureProtectedAccess(obj); | |
| 240 | + } | |
| 241 | + | |
| 242 | + void updateCheck(T obj, V update) { | |
| 243 | + if (!tclass.isInstance(obj) || | |
| 244 | + (update != null && vclass != null && !vclass.isInstance(update))) | |
| 245 | + throw new ClassCastException(); | |
| 246 | + if (cclass != null) | |
| 247 | + ensureProtectedAccess(obj); | |
| 248 | + } | |
| 249 | + | |
| 250 | + public boolean compareAndSet(T obj, V expect, V update) { | |
| 251 | + if (obj == null || obj.getClass() != tclass || cclass != null || | |
| 252 | + (update != null && vclass != null && | |
| 253 | + vclass != update.getClass())) | |
| 254 | + updateCheck(obj, update); | |
| 255 | + return unsafe.compareAndSwapObject(obj, offset, expect, update); | |
| 256 | + } | |
| 257 | + | |
| 258 | + public boolean weakCompareAndSet(T obj, V expect, V update) { | |
| 259 | + // same implementation as strong form for now | |
| 260 | + if (obj == null || obj.getClass() != tclass || cclass != null || | |
| 261 | + (update != null && vclass != null && | |
| 262 | + vclass != update.getClass())) | |
| 263 | + updateCheck(obj, update); | |
| 264 | + return unsafe.compareAndSwapObject(obj, offset, expect, update); | |
| 265 | + } | |
| 266 | + | |
| 267 | + public void set(T obj, V newValue) { | |
| 268 | + if (obj == null || obj.getClass() != tclass || cclass != null || | |
| 269 | + (newValue != null && vclass != null && | |
| 270 | + vclass != newValue.getClass())) | |
| 271 | + updateCheck(obj, newValue); | |
| 272 | + unsafe.putObjectVolatile(obj, offset, newValue); | |
| 273 | + } | |
| 274 | + | |
| 275 | + public void lazySet(T obj, V newValue) { | |
| 276 | + if (obj == null || obj.getClass() != tclass || cclass != null || | |
| 277 | + (newValue != null && vclass != null && | |
| 278 | + vclass != newValue.getClass())) | |
| 279 | + updateCheck(obj, newValue); | |
| 280 | + unsafe.putOrderedObject(obj, offset, newValue); | |
| 281 | + } | |
| 282 | + | |
| 283 | + public V get(T obj) { | |
| 284 | + if (obj == null || obj.getClass() != tclass || cclass != null) | |
| 285 | + targetCheck(obj); | |
| 286 | + return (V)unsafe.getObjectVolatile(obj, offset); | |
| 287 | + } | |
| 288 | + | |
| 289 | + private void ensureProtectedAccess(T obj) { | |
| 290 | + if (cclass.isInstance(obj)) { | |
| 291 | + return; | |
| 292 | + } | |
| 293 | + throw new RuntimeException( | |
| 294 | + new IllegalAccessException("Class " + | |
| 295 | + cclass.getName() + | |
| 296 | + " can not access a protected member of class " + | |
| 297 | + tclass.getName() + | |
| 298 | + " using an instance of " + | |
| 299 | + obj.getClass().getName() | |
| 300 | + ) | |
| 301 | + ); | |
| 302 | + } | |
| 303 | + } | |
| 304 | +} | |