author | dl |
Thu, 07 Apr 2011 15:06:32 +0100 | |
changeset 9242 | ef138d47df58 |
parent 7518 | 0282db800fe1 |
child 11134 | 9ff7640994bf |
permissions | -rw-r--r-- |
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/* |
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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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9242
ef138d47df58
7034657: Update Creative Commons license URL in legal notices
dl
parents:
7518
diff
changeset
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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 sun.misc.Unsafe; |
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import java.lang.reflect.*; |
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/** |
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* A reflection-based utility that enables atomic updates to |
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* designated {@code volatile int} fields of designated classes. |
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* This class is designed for use in atomic data structures in which |
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* several fields of the same node are independently subject to atomic |
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* updates. |
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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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* @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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*/ |
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public abstract class AtomicIntegerFieldUpdater<T> { |
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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 argument is 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 fieldName the name of the field to be updated |
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* @return the updater |
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* @throws IllegalArgumentException if the field is not a |
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* volatile integer type |
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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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*/ |
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public static <U> AtomicIntegerFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) { |
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return new AtomicIntegerFieldUpdaterImpl<U>(tclass, fieldName); |
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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 AtomicIntegerFieldUpdater() { |
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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 true if successful |
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* @throws ClassCastException if {@code obj} is not an instance |
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* of the class possessing the field established in the constructor |
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*/ |
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public abstract boolean compareAndSet(T obj, int expect, int 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>May <a href="package-summary.html#Spurious">fail spuriously</a> |
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* and does not provide ordering guarantees, so is only rarely an |
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* appropriate 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 true if successful |
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* @throws ClassCastException if {@code obj} is not an instance |
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* of the class possessing the field established in the constructor |
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*/ |
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public abstract boolean weakCompareAndSet(T obj, int expect, int 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, int 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, int newValue); |
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/** |
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* Gets the current value held in the field of the given object managed |
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* 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 int 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 int getAndSet(T obj, int newValue) { |
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for (;;) { |
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int current = get(obj); |
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if (compareAndSet(obj, current, newValue)) |
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return current; |
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} |
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} |
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/** |
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* Atomically increments by one the current value of the field of the |
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* given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @return the previous value |
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*/ |
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public int getAndIncrement(T obj) { |
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for (;;) { |
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int current = get(obj); |
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int next = current + 1; |
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if (compareAndSet(obj, current, next)) |
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return current; |
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} |
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} |
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/** |
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* Atomically decrements by one the current value of the field of the |
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* given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @return the previous value |
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*/ |
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public int getAndDecrement(T obj) { |
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for (;;) { |
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int current = get(obj); |
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int next = current - 1; |
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if (compareAndSet(obj, current, next)) |
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return current; |
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} |
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} |
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/** |
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* Atomically adds the given value to the current value of the field of |
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* the given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @param delta the value to add |
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* @return the previous value |
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*/ |
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public int getAndAdd(T obj, int delta) { |
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for (;;) { |
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int current = get(obj); |
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int next = current + delta; |
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if (compareAndSet(obj, current, next)) |
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return current; |
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} |
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} |
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/** |
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* Atomically increments by one the current value of the field of the |
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* given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @return the updated value |
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*/ |
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public int incrementAndGet(T obj) { |
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for (;;) { |
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int current = get(obj); |
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int next = current + 1; |
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if (compareAndSet(obj, current, next)) |
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return next; |
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} |
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} |
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/** |
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* Atomically decrements by one the current value of the field of the |
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* given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @return the updated value |
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*/ |
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public int decrementAndGet(T obj) { |
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for (;;) { |
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int current = get(obj); |
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int next = current - 1; |
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if (compareAndSet(obj, current, next)) |
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return next; |
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} |
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} |
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/** |
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* Atomically adds the given value to the current value of the field of |
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* the given object managed by this updater. |
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* |
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* @param obj An object whose field to get and set |
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* @param delta the value to add |
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* @return the updated value |
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*/ |
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public int addAndGet(T obj, int delta) { |
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for (;;) { |
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int current = get(obj); |
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int next = current + delta; |
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if (compareAndSet(obj, current, next)) |
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return next; |
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} |
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} |
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/** |
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* Standard hotspot implementation using intrinsics |
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*/ |
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private static class AtomicIntegerFieldUpdaterImpl<T> extends AtomicIntegerFieldUpdater<T> { |
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private static final Unsafe unsafe = Unsafe.getUnsafe(); |
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private final long offset; |
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private final Class<T> tclass; |
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private final Class cclass; |
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AtomicIntegerFieldUpdaterImpl(Class<T> tclass, String fieldName) { |
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Field field = null; |
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Class caller = null; |
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int modifiers = 0; |
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try { |
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field = tclass.getDeclaredField(fieldName); |
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caller = sun.reflect.Reflection.getCallerClass(3); |
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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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sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass); |
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} catch (Exception ex) { |
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throw new RuntimeException(ex); |
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} |
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Class fieldt = field.getType(); |
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if (fieldt != int.class) |
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throw new IllegalArgumentException("Must be integer type"); |
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if (!Modifier.isVolatile(modifiers)) |
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throw new IllegalArgumentException("Must be volatile type"); |
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this.cclass = (Modifier.isProtected(modifiers) && |
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caller != tclass) ? caller : null; |
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this.tclass = tclass; |
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offset = unsafe.objectFieldOffset(field); |
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} |
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private void fullCheck(T obj) { |
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if (!tclass.isInstance(obj)) |
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throw new ClassCastException(); |
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if (cclass != null) |
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ensureProtectedAccess(obj); |
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} |
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public boolean compareAndSet(T obj, int expect, int update) { |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj); |
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return unsafe.compareAndSwapInt(obj, offset, expect, update); |
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} |
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public boolean weakCompareAndSet(T obj, int expect, int update) { |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj); |
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return unsafe.compareAndSwapInt(obj, offset, expect, update); |
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} |
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public void set(T obj, int newValue) { |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj); |
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unsafe.putIntVolatile(obj, offset, newValue); |
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} |
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public void lazySet(T obj, int newValue) { |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj); |
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unsafe.putOrderedInt(obj, offset, newValue); |
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} |
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public final int get(T obj) { |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj); |
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return unsafe.getIntVolatile(obj, offset); |
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} |
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private void ensureProtectedAccess(T obj) { |
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if (cclass.isInstance(obj)) { |
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return; |
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} |
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throw new RuntimeException( |
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new IllegalAccessException("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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); |
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} |
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} |
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} |