--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.java Sun Aug 17 15:54:13 2014 +0100
@@ -0,0 +1,448 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent.atomic;
+import java.util.function.UnaryOperator;
+import java.util.function.BinaryOperator;
+import sun.misc.Unsafe;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.security.AccessController;
+import java.security.PrivilegedExceptionAction;
+import java.security.PrivilegedActionException;
+import sun.reflect.CallerSensitive;
+import sun.reflect.Reflection;
+
+/**
+ * A reflection-based utility that enables atomic updates to
+ * designated {@code volatile} reference fields of designated
+ * classes. This class is designed for use in atomic data structures
+ * in which several reference fields of the same node are
+ * independently subject to atomic updates. For example, a tree node
+ * might be declared as
+ *
+ * <pre> {@code
+ * class Node {
+ * private volatile Node left, right;
+ *
+ * private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
+ * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
+ * private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
+ * AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
+ *
+ * Node getLeft() { return left; }
+ * boolean compareAndSetLeft(Node expect, Node update) {
+ * return leftUpdater.compareAndSet(this, expect, update);
+ * }
+ * // ... and so on
+ * }}</pre>
+ *
+ * <p>Note that the guarantees of the {@code compareAndSet}
+ * method in this class are weaker than in other atomic classes.
+ * Because this class cannot ensure that all uses of the field
+ * are appropriate for purposes of atomic access, it can
+ * guarantee atomicity only with respect to other invocations of
+ * {@code compareAndSet} and {@code set} on the same updater.
+ *
+ * @since 1.5
+ * @author Doug Lea
+ * @param <T> The type of the object holding the updatable field
+ * @param <V> The type of the field
+ */
+public abstract class AtomicReferenceFieldUpdater<T,V> {
+
+ /**
+ * Creates and returns an updater for objects with the given field.
+ * The Class arguments are needed to check that reflective types and
+ * generic types match.
+ *
+ * @param tclass the class of the objects holding the field
+ * @param vclass the class of the field
+ * @param fieldName the name of the field to be updated
+ * @param <U> the type of instances of tclass
+ * @param <W> the type of instances of vclass
+ * @return the updater
+ * @throws ClassCastException if the field is of the wrong type
+ * @throws IllegalArgumentException if the field is not volatile
+ * @throws RuntimeException with a nested reflection-based
+ * exception if the class does not hold field or is the wrong type,
+ * or the field is inaccessible to the caller according to Java language
+ * access control
+ */
+ @CallerSensitive
+ public static <U,W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass,
+ Class<W> vclass,
+ String fieldName) {
+ return new AtomicReferenceFieldUpdaterImpl<U,W>
+ (tclass, vclass, fieldName, Reflection.getCallerClass());
+ }
+
+ /**
+ * Protected do-nothing constructor for use by subclasses.
+ */
+ protected AtomicReferenceFieldUpdater() {
+ }
+
+ /**
+ * Atomically sets the field of the given object managed by this updater
+ * to the given updated value if the current value {@code ==} the
+ * expected value. This method is guaranteed to be atomic with respect to
+ * other calls to {@code compareAndSet} and {@code set}, but not
+ * necessarily with respect to other changes in the field.
+ *
+ * @param obj An object whose field to conditionally set
+ * @param expect the expected value
+ * @param update the new value
+ * @return {@code true} if successful
+ */
+ public abstract boolean compareAndSet(T obj, V expect, V update);
+
+ /**
+ * Atomically sets the field of the given object managed by this updater
+ * to the given updated value if the current value {@code ==} the
+ * expected value. This method is guaranteed to be atomic with respect to
+ * other calls to {@code compareAndSet} and {@code set}, but not
+ * necessarily with respect to other changes in the field.
+ *
+ * <p><a href="package-summary.html#weakCompareAndSet">May fail
+ * spuriously and does not provide ordering guarantees</a>, so is
+ * only rarely an appropriate alternative to {@code compareAndSet}.
+ *
+ * @param obj An object whose field to conditionally set
+ * @param expect the expected value
+ * @param update the new value
+ * @return {@code true} if successful
+ */
+ public abstract boolean weakCompareAndSet(T obj, V expect, V update);
+
+ /**
+ * Sets the field of the given object managed by this updater to the
+ * given updated value. This operation is guaranteed to act as a volatile
+ * store with respect to subsequent invocations of {@code compareAndSet}.
+ *
+ * @param obj An object whose field to set
+ * @param newValue the new value
+ */
+ public abstract void set(T obj, V newValue);
+
+ /**
+ * Eventually sets the field of the given object managed by this
+ * updater to the given updated value.
+ *
+ * @param obj An object whose field to set
+ * @param newValue the new value
+ * @since 1.6
+ */
+ public abstract void lazySet(T obj, V newValue);
+
+ /**
+ * Gets the current value held in the field of the given object managed
+ * by this updater.
+ *
+ * @param obj An object whose field to get
+ * @return the current value
+ */
+ public abstract V get(T obj);
+
+ /**
+ * Atomically sets the field of the given object managed by this updater
+ * to the given value and returns the old value.
+ *
+ * @param obj An object whose field to get and set
+ * @param newValue the new value
+ * @return the previous value
+ */
+ public V getAndSet(T obj, V newValue) {
+ V prev;
+ do {
+ prev = get(obj);
+ } while (!compareAndSet(obj, prev, newValue));
+ return prev;
+ }
+
+ /**
+ * Atomically updates the field of the given object managed by this updater
+ * with the results of applying the given function, returning the previous
+ * value. The function should be side-effect-free, since it may be
+ * re-applied when attempted updates fail due to contention among threads.
+ *
+ * @param obj An object whose field to get and set
+ * @param updateFunction a side-effect-free function
+ * @return the previous value
+ * @since 1.8
+ */
+ public final V getAndUpdate(T obj, UnaryOperator<V> updateFunction) {
+ V prev, next;
+ do {
+ prev = get(obj);
+ next = updateFunction.apply(prev);
+ } while (!compareAndSet(obj, prev, next));
+ return prev;
+ }
+
+ /**
+ * Atomically updates the field of the given object managed by this updater
+ * with the results of applying the given function, returning the updated
+ * value. The function should be side-effect-free, since it may be
+ * re-applied when attempted updates fail due to contention among threads.
+ *
+ * @param obj An object whose field to get and set
+ * @param updateFunction a side-effect-free function
+ * @return the updated value
+ * @since 1.8
+ */
+ public final V updateAndGet(T obj, UnaryOperator<V> updateFunction) {
+ V prev, next;
+ do {
+ prev = get(obj);
+ next = updateFunction.apply(prev);
+ } while (!compareAndSet(obj, prev, next));
+ return next;
+ }
+
+ /**
+ * Atomically updates the field of the given object managed by this
+ * updater with the results of applying the given function to the
+ * current and given values, returning the previous value. The
+ * function should be side-effect-free, since it may be re-applied
+ * when attempted updates fail due to contention among threads. The
+ * function is applied with the current value as its first argument,
+ * and the given update as the second argument.
+ *
+ * @param obj An object whose field to get and set
+ * @param x the update value
+ * @param accumulatorFunction a side-effect-free function of two arguments
+ * @return the previous value
+ * @since 1.8
+ */
+ public final V getAndAccumulate(T obj, V x,
+ BinaryOperator<V> accumulatorFunction) {
+ V prev, next;
+ do {
+ prev = get(obj);
+ next = accumulatorFunction.apply(prev, x);
+ } while (!compareAndSet(obj, prev, next));
+ return prev;
+ }
+
+ /**
+ * Atomically updates the field of the given object managed by this
+ * updater with the results of applying the given function to the
+ * current and given values, returning the updated value. The
+ * function should be side-effect-free, since it may be re-applied
+ * when attempted updates fail due to contention among threads. The
+ * function is applied with the current value as its first argument,
+ * and the given update as the second argument.
+ *
+ * @param obj An object whose field to get and set
+ * @param x the update value
+ * @param accumulatorFunction a side-effect-free function of two arguments
+ * @return the updated value
+ * @since 1.8
+ */
+ public final V accumulateAndGet(T obj, V x,
+ BinaryOperator<V> accumulatorFunction) {
+ V prev, next;
+ do {
+ prev = get(obj);
+ next = accumulatorFunction.apply(prev, x);
+ } while (!compareAndSet(obj, prev, next));
+ return next;
+ }
+
+ private static final class AtomicReferenceFieldUpdaterImpl<T,V>
+ extends AtomicReferenceFieldUpdater<T,V> {
+ private static final Unsafe unsafe = Unsafe.getUnsafe();
+ private final long offset;
+ private final Class<T> tclass;
+ private final Class<V> vclass;
+ private final Class<?> cclass;
+
+ /*
+ * Internal type checks within all update methods contain
+ * internal inlined optimizations checking for the common
+ * cases where the class is final (in which case a simple
+ * getClass comparison suffices) or is of type Object (in
+ * which case no check is needed because all objects are
+ * instances of Object). The Object case is handled simply by
+ * setting vclass to null in constructor. The targetCheck and
+ * updateCheck methods are invoked when these faster
+ * screenings fail.
+ */
+
+ AtomicReferenceFieldUpdaterImpl(final Class<T> tclass,
+ final Class<V> vclass,
+ final String fieldName,
+ final Class<?> caller) {
+ final Field field;
+ final Class<?> fieldClass;
+ final int modifiers;
+ try {
+ field = AccessController.doPrivileged(
+ new PrivilegedExceptionAction<Field>() {
+ public Field run() throws NoSuchFieldException {
+ return tclass.getDeclaredField(fieldName);
+ }
+ });
+ modifiers = field.getModifiers();
+ sun.reflect.misc.ReflectUtil.ensureMemberAccess(
+ caller, tclass, null, modifiers);
+ ClassLoader cl = tclass.getClassLoader();
+ ClassLoader ccl = caller.getClassLoader();
+ if ((ccl != null) && (ccl != cl) &&
+ ((cl == null) || !isAncestor(cl, ccl))) {
+ sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
+ }
+ fieldClass = field.getType();
+ } catch (PrivilegedActionException pae) {
+ throw new RuntimeException(pae.getException());
+ } catch (Exception ex) {
+ throw new RuntimeException(ex);
+ }
+
+ if (vclass != fieldClass)
+ throw new ClassCastException();
+ if (vclass.isPrimitive())
+ throw new IllegalArgumentException("Must be reference type");
+
+ if (!Modifier.isVolatile(modifiers))
+ throw new IllegalArgumentException("Must be volatile type");
+
+ this.cclass = (Modifier.isProtected(modifiers) &&
+ caller != tclass) ? caller : null;
+ this.tclass = tclass;
+ if (vclass == Object.class)
+ this.vclass = null;
+ else
+ this.vclass = vclass;
+ offset = unsafe.objectFieldOffset(field);
+ }
+
+ /**
+ * Returns true if the second classloader can be found in the first
+ * classloader's delegation chain.
+ * Equivalent to the inaccessible: first.isAncestor(second).
+ */
+ private static boolean isAncestor(ClassLoader first, ClassLoader second) {
+ ClassLoader acl = first;
+ do {
+ acl = acl.getParent();
+ if (second == acl) {
+ return true;
+ }
+ } while (acl != null);
+ return false;
+ }
+
+ void targetCheck(T obj) {
+ if (!tclass.isInstance(obj))
+ throw new ClassCastException();
+ if (cclass != null)
+ ensureProtectedAccess(obj);
+ }
+
+ void updateCheck(T obj, V update) {
+ if (!tclass.isInstance(obj) ||
+ (update != null && vclass != null && !vclass.isInstance(update)))
+ throw new ClassCastException();
+ if (cclass != null)
+ ensureProtectedAccess(obj);
+ }
+
+ public boolean compareAndSet(T obj, V expect, V update) {
+ if (obj == null || obj.getClass() != tclass || cclass != null ||
+ (update != null && vclass != null &&
+ vclass != update.getClass()))
+ updateCheck(obj, update);
+ return unsafe.compareAndSwapObject(obj, offset, expect, update);
+ }
+
+ public boolean weakCompareAndSet(T obj, V expect, V update) {
+ // same implementation as strong form for now
+ if (obj == null || obj.getClass() != tclass || cclass != null ||
+ (update != null && vclass != null &&
+ vclass != update.getClass()))
+ updateCheck(obj, update);
+ return unsafe.compareAndSwapObject(obj, offset, expect, update);
+ }
+
+ public void set(T obj, V newValue) {
+ if (obj == null || obj.getClass() != tclass || cclass != null ||
+ (newValue != null && vclass != null &&
+ vclass != newValue.getClass()))
+ updateCheck(obj, newValue);
+ unsafe.putObjectVolatile(obj, offset, newValue);
+ }
+
+ public void lazySet(T obj, V newValue) {
+ if (obj == null || obj.getClass() != tclass || cclass != null ||
+ (newValue != null && vclass != null &&
+ vclass != newValue.getClass()))
+ updateCheck(obj, newValue);
+ unsafe.putOrderedObject(obj, offset, newValue);
+ }
+
+ @SuppressWarnings("unchecked")
+ public V get(T obj) {
+ if (obj == null || obj.getClass() != tclass || cclass != null)
+ targetCheck(obj);
+ return (V)unsafe.getObjectVolatile(obj, offset);
+ }
+
+ @SuppressWarnings("unchecked")
+ public V getAndSet(T obj, V newValue) {
+ if (obj == null || obj.getClass() != tclass || cclass != null ||
+ (newValue != null && vclass != null &&
+ vclass != newValue.getClass()))
+ updateCheck(obj, newValue);
+ return (V)unsafe.getAndSetObject(obj, offset, newValue);
+ }
+
+ private void ensureProtectedAccess(T obj) {
+ if (cclass.isInstance(obj)) {
+ return;
+ }
+ throw new RuntimeException(
+ new IllegalAccessException("Class " +
+ cclass.getName() +
+ " can not access a protected member of class " +
+ tclass.getName() +
+ " using an instance of " +
+ obj.getClass().getName()
+ )
+ );
+ }
+ }
+}