rt/emul/compact/src/main/java/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.java
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1.2 +++ b/rt/emul/compact/src/main/java/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.java Mon Feb 09 20:31:09 2015 +0100
1.3 @@ -0,0 +1,304 @@
1.4 +/*
1.5 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.6 + *
1.7 + * This code is free software; you can redistribute it and/or modify it
1.8 + * under the terms of the GNU General Public License version 2 only, as
1.9 + * published by the Free Software Foundation. Oracle designates this
1.10 + * particular file as subject to the "Classpath" exception as provided
1.11 + * by Oracle in the LICENSE file that accompanied this code.
1.12 + *
1.13 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.14 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.15 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.16 + * version 2 for more details (a copy is included in the LICENSE file that
1.17 + * accompanied this code).
1.18 + *
1.19 + * You should have received a copy of the GNU General Public License version
1.20 + * 2 along with this work; if not, write to the Free Software Foundation,
1.21 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.22 + *
1.23 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.24 + * or visit www.oracle.com if you need additional information or have any
1.25 + * questions.
1.26 + */
1.27 +
1.28 +/*
1.29 + * This file is available under and governed by the GNU General Public
1.30 + * License version 2 only, as published by the Free Software Foundation.
1.31 + * However, the following notice accompanied the original version of this
1.32 + * file:
1.33 + *
1.34 + * Written by Doug Lea with assistance from members of JCP JSR-166
1.35 + * Expert Group and released to the public domain, as explained at
1.36 + * http://creativecommons.org/publicdomain/zero/1.0/
1.37 + */
1.38 +
1.39 +package java.util.concurrent.atomic;
1.40 +import sun.misc.Unsafe;
1.41 +import java.lang.reflect.*;
1.42 +
1.43 +/**
1.44 + * A reflection-based utility that enables atomic updates to
1.45 + * designated {@code volatile} reference fields of designated
1.46 + * classes. This class is designed for use in atomic data structures
1.47 + * in which several reference fields of the same node are
1.48 + * independently subject to atomic updates. For example, a tree node
1.49 + * might be declared as
1.50 + *
1.51 + * <pre> {@code
1.52 + * class Node {
1.53 + * private volatile Node left, right;
1.54 + *
1.55 + * private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
1.56 + * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
1.57 + * private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
1.58 + * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
1.59 + *
1.60 + * Node getLeft() { return left; }
1.61 + * boolean compareAndSetLeft(Node expect, Node update) {
1.62 + * return leftUpdater.compareAndSet(this, expect, update);
1.63 + * }
1.64 + * // ... and so on
1.65 + * }}</pre>
1.66 + *
1.67 + * <p>Note that the guarantees of the {@code compareAndSet}
1.68 + * method in this class are weaker than in other atomic classes.
1.69 + * Because this class cannot ensure that all uses of the field
1.70 + * are appropriate for purposes of atomic access, it can
1.71 + * guarantee atomicity only with respect to other invocations of
1.72 + * {@code compareAndSet} and {@code set} on the same updater.
1.73 + *
1.74 + * @since 1.5
1.75 + * @author Doug Lea
1.76 + * @param <T> The type of the object holding the updatable field
1.77 + * @param <V> The type of the field
1.78 + */
1.79 +public abstract class AtomicReferenceFieldUpdater<T, V> {
1.80 +
1.81 + /**
1.82 + * Creates and returns an updater for objects with the given field.
1.83 + * The Class arguments are needed to check that reflective types and
1.84 + * generic types match.
1.85 + *
1.86 + * @param tclass the class of the objects holding the field.
1.87 + * @param vclass the class of the field
1.88 + * @param fieldName the name of the field to be updated.
1.89 + * @return the updater
1.90 + * @throws IllegalArgumentException if the field is not a volatile reference type.
1.91 + * @throws RuntimeException with a nested reflection-based
1.92 + * exception if the class does not hold field or is the wrong type.
1.93 + */
1.94 + public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) {
1.95 + return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass,
1.96 + vclass,
1.97 + fieldName);
1.98 + }
1.99 +
1.100 + /**
1.101 + * Protected do-nothing constructor for use by subclasses.
1.102 + */
1.103 + protected AtomicReferenceFieldUpdater() {
1.104 + }
1.105 +
1.106 + /**
1.107 + * Atomically sets the field of the given object managed by this updater
1.108 + * to the given updated value if the current value {@code ==} the
1.109 + * expected value. This method is guaranteed to be atomic with respect to
1.110 + * other calls to {@code compareAndSet} and {@code set}, but not
1.111 + * necessarily with respect to other changes in the field.
1.112 + *
1.113 + * @param obj An object whose field to conditionally set
1.114 + * @param expect the expected value
1.115 + * @param update the new value
1.116 + * @return true if successful.
1.117 + */
1.118 + public abstract boolean compareAndSet(T obj, V expect, V update);
1.119 +
1.120 + /**
1.121 + * Atomically sets the field of the given object managed by this updater
1.122 + * to the given updated value if the current value {@code ==} the
1.123 + * expected value. This method is guaranteed to be atomic with respect to
1.124 + * other calls to {@code compareAndSet} and {@code set}, but not
1.125 + * necessarily with respect to other changes in the field.
1.126 + *
1.127 + * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
1.128 + * and does not provide ordering guarantees, so is only rarely an
1.129 + * appropriate alternative to {@code compareAndSet}.
1.130 + *
1.131 + * @param obj An object whose field to conditionally set
1.132 + * @param expect the expected value
1.133 + * @param update the new value
1.134 + * @return true if successful.
1.135 + */
1.136 + public abstract boolean weakCompareAndSet(T obj, V expect, V update);
1.137 +
1.138 + /**
1.139 + * Sets the field of the given object managed by this updater to the
1.140 + * given updated value. This operation is guaranteed to act as a volatile
1.141 + * store with respect to subsequent invocations of {@code compareAndSet}.
1.142 + *
1.143 + * @param obj An object whose field to set
1.144 + * @param newValue the new value
1.145 + */
1.146 + public abstract void set(T obj, V newValue);
1.147 +
1.148 + /**
1.149 + * Eventually sets the field of the given object managed by this
1.150 + * updater to the given updated value.
1.151 + *
1.152 + * @param obj An object whose field to set
1.153 + * @param newValue the new value
1.154 + * @since 1.6
1.155 + */
1.156 + public abstract void lazySet(T obj, V newValue);
1.157 +
1.158 + /**
1.159 + * Gets the current value held in the field of the given object managed
1.160 + * by this updater.
1.161 + *
1.162 + * @param obj An object whose field to get
1.163 + * @return the current value
1.164 + */
1.165 + public abstract V get(T obj);
1.166 +
1.167 + /**
1.168 + * Atomically sets the field of the given object managed by this updater
1.169 + * to the given value and returns the old value.
1.170 + *
1.171 + * @param obj An object whose field to get and set
1.172 + * @param newValue the new value
1.173 + * @return the previous value
1.174 + */
1.175 + public V getAndSet(T obj, V newValue) {
1.176 + for (;;) {
1.177 + V current = get(obj);
1.178 + if (compareAndSet(obj, current, newValue))
1.179 + return current;
1.180 + }
1.181 + }
1.182 +
1.183 + private static final class AtomicReferenceFieldUpdaterImpl<T,V>
1.184 + extends AtomicReferenceFieldUpdater<T,V> {
1.185 + private static final Unsafe unsafe = Unsafe.getUnsafe();
1.186 + private final long offset;
1.187 + private final Class<T> tclass;
1.188 + private final Class<V> vclass;
1.189 + private final Class cclass;
1.190 +
1.191 + /*
1.192 + * Internal type checks within all update methods contain
1.193 + * internal inlined optimizations checking for the common
1.194 + * cases where the class is final (in which case a simple
1.195 + * getClass comparison suffices) or is of type Object (in
1.196 + * which case no check is needed because all objects are
1.197 + * instances of Object). The Object case is handled simply by
1.198 + * setting vclass to null in constructor. The targetCheck and
1.199 + * updateCheck methods are invoked when these faster
1.200 + * screenings fail.
1.201 + */
1.202 +
1.203 + AtomicReferenceFieldUpdaterImpl(Class<T> tclass,
1.204 + Class<V> vclass,
1.205 + String fieldName) {
1.206 + Field field = null;
1.207 + Class fieldClass = null;
1.208 + Class caller = null;
1.209 + int modifiers = 0;
1.210 + try {
1.211 + field = tclass.getDeclaredField(fieldName);
1.212 + caller = sun.reflect.Reflection.getCallerClass(3);
1.213 + modifiers = field.getModifiers();
1.214 + sun.reflect.misc.ReflectUtil.ensureMemberAccess(
1.215 + caller, tclass, null, modifiers);
1.216 + sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
1.217 + fieldClass = field.getType();
1.218 + } catch (Exception ex) {
1.219 + throw new RuntimeException(ex);
1.220 + }
1.221 +
1.222 + if (vclass != fieldClass)
1.223 + throw new ClassCastException();
1.224 +
1.225 + if (!Modifier.isVolatile(modifiers))
1.226 + throw new IllegalArgumentException("Must be volatile type");
1.227 +
1.228 + this.cclass = (Modifier.isProtected(modifiers) &&
1.229 + caller != tclass) ? caller : null;
1.230 + this.tclass = tclass;
1.231 + if (vclass == Object.class)
1.232 + this.vclass = null;
1.233 + else
1.234 + this.vclass = vclass;
1.235 + offset = unsafe.objectFieldOffset(field);
1.236 + }
1.237 +
1.238 + void targetCheck(T obj) {
1.239 + if (!tclass.isInstance(obj))
1.240 + throw new ClassCastException();
1.241 + if (cclass != null)
1.242 + ensureProtectedAccess(obj);
1.243 + }
1.244 +
1.245 + void updateCheck(T obj, V update) {
1.246 + if (!tclass.isInstance(obj) ||
1.247 + (update != null && vclass != null && !vclass.isInstance(update)))
1.248 + throw new ClassCastException();
1.249 + if (cclass != null)
1.250 + ensureProtectedAccess(obj);
1.251 + }
1.252 +
1.253 + public boolean compareAndSet(T obj, V expect, V update) {
1.254 + if (obj == null || obj.getClass() != tclass || cclass != null ||
1.255 + (update != null && vclass != null &&
1.256 + vclass != update.getClass()))
1.257 + updateCheck(obj, update);
1.258 + return unsafe.compareAndSwapObject(obj, offset, expect, update);
1.259 + }
1.260 +
1.261 + public boolean weakCompareAndSet(T obj, V expect, V update) {
1.262 + // same implementation as strong form for now
1.263 + if (obj == null || obj.getClass() != tclass || cclass != null ||
1.264 + (update != null && vclass != null &&
1.265 + vclass != update.getClass()))
1.266 + updateCheck(obj, update);
1.267 + return unsafe.compareAndSwapObject(obj, offset, expect, update);
1.268 + }
1.269 +
1.270 + public void set(T obj, V newValue) {
1.271 + if (obj == null || obj.getClass() != tclass || cclass != null ||
1.272 + (newValue != null && vclass != null &&
1.273 + vclass != newValue.getClass()))
1.274 + updateCheck(obj, newValue);
1.275 + unsafe.putObjectVolatile(obj, offset, newValue);
1.276 + }
1.277 +
1.278 + public void lazySet(T obj, V newValue) {
1.279 + if (obj == null || obj.getClass() != tclass || cclass != null ||
1.280 + (newValue != null && vclass != null &&
1.281 + vclass != newValue.getClass()))
1.282 + updateCheck(obj, newValue);
1.283 + unsafe.putOrderedObject(obj, offset, newValue);
1.284 + }
1.285 +
1.286 + public V get(T obj) {
1.287 + if (obj == null || obj.getClass() != tclass || cclass != null)
1.288 + targetCheck(obj);
1.289 + return (V)unsafe.getObjectVolatile(obj, offset);
1.290 + }
1.291 +
1.292 + private void ensureProtectedAccess(T obj) {
1.293 + if (cclass.isInstance(obj)) {
1.294 + return;
1.295 + }
1.296 + throw new RuntimeException(
1.297 + new IllegalAccessException("Class " +
1.298 + cclass.getName() +
1.299 + " can not access a protected member of class " +
1.300 + tclass.getName() +
1.301 + " using an instance of " +
1.302 + obj.getClass().getName()
1.303 + )
1.304 + );
1.305 + }
1.306 + }
1.307 +}