/* * 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 sun.misc.Unsafe;import java.lang.reflect.*; /** * 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. * @return the updater * @throws IllegalArgumentException if the field is not a volatile reference type. * @throws RuntimeException with a nested reflection-based * exception if the class does not hold field or is the wrong type. */ public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) { return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass, vclass, fieldName); } /** * 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 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>May <a href="package-summary.html#Spurious">fail spuriously</a> * and does not provide ordering guarantees, 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 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) { for (;;) { V current = get(obj); if (compareAndSet(obj, current, newValue)) return current; } } 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(Class<T> tclass, Class<V> vclass, String fieldName) { Field field = null; Class fieldClass = null; Class caller = null; int modifiers = 0; try { field = tclass.getDeclaredField(fieldName); caller = sun.reflect.Reflection.getCallerClass(3); modifiers = field.getModifiers(); sun.reflect.misc.ReflectUtil.ensureMemberAccess( caller, tclass, null, modifiers); sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass); fieldClass = field.getType(); } catch (Exception ex) { throw new RuntimeException(ex); } if (vclass != fieldClass) throw new ClassCastException(); 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); } 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); } public V get(T obj) { if (obj == null || obj.getClass() != tclass || cclass != null) targetCheck(obj); return (V)unsafe.getObjectVolatile(obj, offset); } 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() ) ); } }}
/*
* 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 sun.misc.Unsafe;
import java.lang.reflect.*;
/**
* 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.
* @return the updater
* @throws IllegalArgumentException if the field is not a volatile reference type.
* @throws RuntimeException with a nested reflection-based
* exception if the class does not hold field or is the wrong type.
*/
public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) {
return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass,
vclass,
fieldName);
}
/**
* 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 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>May <a href="package-summary.html#Spurious">fail spuriously</a>
* and does not provide ordering guarantees, 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 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) {
for (;;) {
V current = get(obj);
if (compareAndSet(obj, current, newValue))
return current;
}
}
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(Class<T> tclass,
Class<V> vclass,
String fieldName) {
Field field = null;
Class fieldClass = null;
Class caller = null;
int modifiers = 0;
try {
field = tclass.getDeclaredField(fieldName);
caller = sun.reflect.Reflection.getCallerClass(3);
modifiers = field.getModifiers();
sun.reflect.misc.ReflectUtil.ensureMemberAccess(
caller, tclass, null, modifiers);
sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
fieldClass = field.getType();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
if (vclass != fieldClass)
throw new ClassCastException();
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);
}
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);
}
public V get(T obj) {
if (obj == null || obj.getClass() != tclass || cclass != null)
targetCheck(obj);
return (V)unsafe.getObjectVolatile(obj, offset);
}
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()
)
);
}
}
}