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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 | } | ||