491 lines
19 KiB
Java
491 lines
19 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent.atomic;
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import java.lang.reflect.Field;
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import java.lang.reflect.Modifier;
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import java.security.AccessController;
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import java.security.PrivilegedActionException;
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import java.security.PrivilegedExceptionAction;
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import java.util.function.BinaryOperator;
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import java.util.function.UnaryOperator;
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import jdk.internal.misc.Unsafe;
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import jdk.internal.reflect.CallerSensitive;
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import jdk.internal.reflect.Reflection;
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import java.lang.invoke.VarHandle;
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/**
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* A reflection-based utility that enables atomic updates to
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* designated {@code volatile} reference fields of designated
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* classes. This class is designed for use in atomic data structures
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* in which several reference fields of the same node are
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* independently subject to atomic updates. For example, a tree node
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* might be declared as
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*
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* <pre> {@code
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* class Node {
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* private volatile Node left, right;
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*
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* private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
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* AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
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* private static final AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
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* AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
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*
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* Node getLeft() { return left; }
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* boolean compareAndSetLeft(Node expect, Node update) {
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* return leftUpdater.compareAndSet(this, expect, update);
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* }
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* // ... and so on
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* }}</pre>
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*
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* <p>Note that the guarantees of the {@code compareAndSet}
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* method in this class are weaker than in other atomic classes.
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* Because this class cannot ensure that all uses of the field
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* are appropriate for purposes of atomic access, it can
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* guarantee atomicity only with respect to other invocations of
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* {@code compareAndSet} and {@code set} on the same updater.
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*
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* <p>Object arguments for parameters of type {@code T} that are not
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* instances of the class passed to {@link #newUpdater} will result in
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* a {@link ClassCastException} being thrown.
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*
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* @since 1.5
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* @author Doug Lea
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* @param <T> The type of the object holding the updatable field
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* @param <V> The type of the field
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*/
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public abstract class AtomicReferenceFieldUpdater<T,V> {
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/**
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* Creates and returns an updater for objects with the given field.
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* The Class arguments are needed to check that reflective types and
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* generic types match.
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*
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* @param tclass the class of the objects holding the field
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* @param vclass the class of the field
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* @param fieldName the name of the field to be updated
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* @param <U> the type of instances of tclass
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* @param <W> the type of instances of vclass
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* @return the updater
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* @throws ClassCastException if the field is of the wrong type
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* @throws IllegalArgumentException if the field is not volatile
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* @throws RuntimeException with a nested reflection-based
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* exception if the class does not hold field or is the wrong type,
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* or the field is inaccessible to the caller according to Java language
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* access control
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*/
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@CallerSensitive
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public static <U,W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass,
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Class<W> vclass,
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String fieldName) {
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return new AtomicReferenceFieldUpdaterImpl<U,W>
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(tclass, vclass, fieldName, Reflection.getCallerClass());
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}
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/**
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* Protected do-nothing constructor for use by subclasses.
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*/
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protected AtomicReferenceFieldUpdater() {
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}
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given updated value if the current value {@code ==} the
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* expected value. This method is guaranteed to be atomic with respect to
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* other calls to {@code compareAndSet} and {@code set}, but not
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* necessarily with respect to other changes in the field.
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*
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* @param obj An object whose field to conditionally set
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* @param expect the expected value
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* @param update the new value
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* @return {@code true} if successful
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*/
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public abstract boolean compareAndSet(T obj, V expect, V update);
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given updated value if the current value {@code ==} the
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* expected value. This method is guaranteed to be atomic with respect to
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* other calls to {@code compareAndSet} and {@code set}, but not
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* necessarily with respect to other changes in the field.
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*
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* <p>This operation may fail spuriously and does not provide
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* ordering guarantees, so is only rarely an appropriate
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* alternative to {@code compareAndSet}.
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*
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* @param obj An object whose field to conditionally set
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* @param expect the expected value
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* @param update the new value
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* @return {@code true} if successful
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*/
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public abstract boolean weakCompareAndSet(T obj, V expect, V update);
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/**
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* Sets the field of the given object managed by this updater to the
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* given updated value. This operation is guaranteed to act as a volatile
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* store with respect to subsequent invocations of {@code compareAndSet}.
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*
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* @param obj An object whose field to set
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* @param newValue the new value
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*/
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public abstract void set(T obj, V newValue);
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/**
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* Eventually sets the field of the given object managed by this
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* updater to the given updated value.
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*
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* @param obj An object whose field to set
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* @param newValue the new value
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* @since 1.6
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*/
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public abstract void lazySet(T obj, V newValue);
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/**
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* Returns the current value held in the field of the given object
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* managed by this updater.
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*
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* @param obj An object whose field to get
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* @return the current value
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*/
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public abstract V get(T obj);
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given value and returns the old value.
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*
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* @param obj An object whose field to get and set
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* @param newValue the new value
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* @return the previous value
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*/
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public V getAndSet(T obj, V newValue) {
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V prev;
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do {
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prev = get(obj);
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} while (!compareAndSet(obj, prev, newValue));
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return prev;
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}
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/**
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* Atomically updates (with memory effects as specified by {@link
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* VarHandle#compareAndSet}) the field of the given object managed
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* by this updater with the results of applying the given
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* function, returning the previous value. The function should be
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* side-effect-free, since it may be re-applied when attempted
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* updates fail due to contention among threads.
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*
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* @param obj An object whose field to get and set
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* @param updateFunction a side-effect-free function
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* @return the previous value
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* @since 1.8
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*/
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public final V getAndUpdate(T obj, UnaryOperator<V> updateFunction) {
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V prev, next;
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do {
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prev = get(obj);
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next = updateFunction.apply(prev);
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} while (!compareAndSet(obj, prev, next));
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return prev;
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}
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/**
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* Atomically updates (with memory effects as specified by {@link
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* VarHandle#compareAndSet}) the field of the given object managed
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* by this updater with the results of applying the given
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* function, returning the updated value. The function should be
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* side-effect-free, since it may be re-applied when attempted
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* updates fail due to contention among threads.
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*
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* @param obj An object whose field to get and set
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* @param updateFunction a side-effect-free function
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* @return the updated value
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* @since 1.8
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*/
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public final V updateAndGet(T obj, UnaryOperator<V> updateFunction) {
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V prev, next;
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do {
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prev = get(obj);
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next = updateFunction.apply(prev);
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} while (!compareAndSet(obj, prev, next));
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return next;
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}
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/**
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* Atomically updates (with memory effects as specified by {@link
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* VarHandle#compareAndSet}) the field of the given object managed
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* by this updater with the results of applying the given function
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* to the current and given values, returning the previous value.
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* The function should be side-effect-free, since it may be
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* re-applied when attempted updates fail due to contention among
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* threads. The function is applied with the current value as its
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* first argument, and the given update as the second argument.
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*
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* @param obj An object whose field to get and set
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* @param x the update value
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* @param accumulatorFunction a side-effect-free function of two arguments
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* @return the previous value
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* @since 1.8
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*/
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public final V getAndAccumulate(T obj, V x,
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BinaryOperator<V> accumulatorFunction) {
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V prev, next;
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do {
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prev = get(obj);
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next = accumulatorFunction.apply(prev, x);
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} while (!compareAndSet(obj, prev, next));
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return prev;
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}
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/**
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* Atomically updates (with memory effects as specified by {@link
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* VarHandle#compareAndSet}) the field of the given object managed
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* by this updater with the results of applying the given function
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* to the current and given values, returning the updated value.
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* The function should be side-effect-free, since it may be
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* re-applied when attempted updates fail due to contention among
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* threads. The function is applied with the current value as its
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* first argument, and the given update as the second argument.
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*
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* @param obj An object whose field to get and set
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* @param x the update value
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* @param accumulatorFunction a side-effect-free function of two arguments
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* @return the updated value
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* @since 1.8
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*/
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public final V accumulateAndGet(T obj, V x,
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BinaryOperator<V> accumulatorFunction) {
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V prev, next;
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do {
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prev = get(obj);
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next = accumulatorFunction.apply(prev, x);
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} while (!compareAndSet(obj, prev, next));
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return next;
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}
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private static final class AtomicReferenceFieldUpdaterImpl<T,V>
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extends AtomicReferenceFieldUpdater<T,V> {
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private static final Unsafe U = Unsafe.getUnsafe();
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private final long offset;
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/**
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* if field is protected, the subclass constructing updater, else
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* the same as tclass
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*/
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private final Class<?> cclass;
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/** class holding the field */
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private final Class<T> tclass;
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/** field value type */
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private final Class<V> vclass;
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/*
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* Internal type checks within all update methods contain
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* internal inlined optimizations checking for the common
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* cases where the class is final (in which case a simple
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* getClass comparison suffices) or is of type Object (in
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* which case no check is needed because all objects are
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* instances of Object). The Object case is handled simply by
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* setting vclass to null in constructor. The targetCheck and
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* updateCheck methods are invoked when these faster
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* screenings fail.
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*/
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@SuppressWarnings("removal")
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AtomicReferenceFieldUpdaterImpl(final Class<T> tclass,
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final Class<V> vclass,
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final String fieldName,
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final Class<?> caller) {
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final Field field;
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final Class<?> fieldClass;
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final int modifiers;
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try {
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// Android-changed: Skip privilege escalation which is a noop on Android.
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/*
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field = AccessController.doPrivileged(
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new PrivilegedExceptionAction<Field>() {
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public Field run() throws NoSuchFieldException {
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return tclass.getDeclaredField(fieldName);
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}
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});
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*/
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field = tclass.getDeclaredField(fieldName);
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modifiers = field.getModifiers();
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sun.reflect.misc.ReflectUtil.ensureMemberAccess(
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caller, tclass, null, modifiers);
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// Android-removed: Skip checkPackageAccess which is a noop on Android.
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/*
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ClassLoader cl = tclass.getClassLoader();
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ClassLoader ccl = caller.getClassLoader();
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if ((ccl != null) && (ccl != cl) &&
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((cl == null) || !isAncestor(cl, ccl))) {
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sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
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}
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*/
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fieldClass = field.getType();
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// Android-removed: Skip privilege escalation which is a noop on Android.
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/*
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} catch (PrivilegedActionException pae) {
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throw new RuntimeException(pae.getException());
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*/
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} catch (Exception ex) {
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throw new RuntimeException(ex);
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}
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if (vclass != fieldClass)
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throw new ClassCastException();
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if (vclass.isPrimitive())
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throw new IllegalArgumentException("Must be reference type");
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if (!Modifier.isVolatile(modifiers))
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throw new IllegalArgumentException("Must be volatile type");
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// Access to protected field members is restricted to receivers only
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// of the accessing class, or one of its subclasses, and the
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// accessing class must in turn be a subclass (or package sibling)
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// of the protected member's defining class.
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// If the updater refers to a protected field of a declaring class
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// outside the current package, the receiver argument will be
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// narrowed to the type of the accessing class.
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this.cclass = (Modifier.isProtected(modifiers) &&
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tclass.isAssignableFrom(caller) &&
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!isSamePackage(tclass, caller))
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? caller : tclass;
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this.tclass = tclass;
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this.vclass = vclass;
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this.offset = U.objectFieldOffset(field);
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}
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// Android-removed: isAncestor's only usage was removed above.
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/*
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/**
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* Returns true if the second classloader can be found in the first
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* classloader's delegation chain.
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* Equivalent to the inaccessible: first.isAncestor(second).
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*
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private static boolean isAncestor(ClassLoader first, ClassLoader second) {
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ClassLoader acl = first;
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do {
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acl = acl.getParent();
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if (second == acl) {
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return true;
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}
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} while (acl != null);
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return false;
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}
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*/
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/**
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* Returns true if the two classes have the same class loader and
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* package qualifier
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*/
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private static boolean isSamePackage(Class<?> class1, Class<?> class2) {
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return class1.getClassLoader() == class2.getClassLoader()
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&& class1.getPackageName() == class2.getPackageName();
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}
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/**
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* Checks that target argument is instance of cclass. On
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* failure, throws cause.
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*/
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private final void accessCheck(T obj) {
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if (!cclass.isInstance(obj))
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throwAccessCheckException(obj);
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}
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/**
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* Throws access exception if accessCheck failed due to
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* protected access, else ClassCastException.
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*/
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private final void throwAccessCheckException(T obj) {
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if (cclass == tclass)
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throw new ClassCastException();
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else
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throw new RuntimeException(
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new IllegalAccessException(
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"Class " +
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cclass.getName() +
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" can not access a protected member of class " +
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tclass.getName() +
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" using an instance of " +
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obj.getClass().getName()));
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}
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private final void valueCheck(V v) {
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if (v != null && !(vclass.isInstance(v)))
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throwCCE();
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}
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static void throwCCE() {
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throw new ClassCastException();
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}
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public final boolean compareAndSet(T obj, V expect, V update) {
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accessCheck(obj);
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valueCheck(update);
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return U.compareAndSetReference(obj, offset, expect, update);
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}
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public final boolean weakCompareAndSet(T obj, V expect, V update) {
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// same implementation as strong form for now
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accessCheck(obj);
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valueCheck(update);
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return U.compareAndSetReference(obj, offset, expect, update);
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}
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public final void set(T obj, V newValue) {
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accessCheck(obj);
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valueCheck(newValue);
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U.putReferenceVolatile(obj, offset, newValue);
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}
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public final void lazySet(T obj, V newValue) {
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accessCheck(obj);
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valueCheck(newValue);
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U.putReferenceRelease(obj, offset, newValue);
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}
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@SuppressWarnings("unchecked")
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public final V get(T obj) {
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accessCheck(obj);
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return (V)U.getReferenceVolatile(obj, offset);
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}
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@SuppressWarnings("unchecked")
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public final V getAndSet(T obj, V newValue) {
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accessCheck(obj);
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valueCheck(newValue);
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return (V)U.getAndSetReference(obj, offset, newValue);
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}
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}
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}
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