author | dl |
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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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* 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.util.function.UnaryOperator; |
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import java.util.function.BinaryOperator; |
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import sun.misc.Unsafe; |
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/** |
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* An object reference that may be updated atomically. See the {@link |
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* java.util.concurrent.atomic} package specification for description |
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* of the properties of atomic variables. |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <V> The type of object referred to by this reference |
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*/ |
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public class AtomicReference<V> implements java.io.Serializable { |
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private static final long serialVersionUID = -1848883965231344442L; |
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private static final Unsafe unsafe = Unsafe.getUnsafe(); |
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private static final long valueOffset; |
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static { |
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try { |
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valueOffset = unsafe.objectFieldOffset |
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(AtomicReference.class.getDeclaredField("value")); |
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} catch (Exception ex) { throw new Error(ex); } |
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} |
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private volatile V value; |
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/** |
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* Creates a new AtomicReference with the given initial value. |
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* |
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* @param initialValue the initial value |
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*/ |
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public AtomicReference(V initialValue) { |
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value = initialValue; |
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} |
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/** |
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* Creates a new AtomicReference with null initial value. |
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*/ |
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public AtomicReference() { |
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} |
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/** |
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* Gets the current value. |
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* |
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* @return the current value |
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*/ |
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public final V get() { |
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return value; |
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} |
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/** |
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* Sets to the given value. |
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* |
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* @param newValue the new value |
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*/ |
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public final void set(V newValue) { |
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value = newValue; |
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} |
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/** |
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* Eventually sets to the given value. |
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* |
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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 final void lazySet(V newValue) { |
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unsafe.putOrderedObject(this, valueOffset, newValue); |
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} |
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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} the expected value. |
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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. False return indicates that |
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* the actual value was not equal to the expected value. |
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*/ |
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public final boolean compareAndSet(V expect, V update) { |
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return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
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} |
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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} the expected value. |
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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 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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*/ |
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public final boolean weakCompareAndSet(V expect, V update) { |
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return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
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} |
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/** |
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* Atomically sets to the given value and returns the old value. |
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* |
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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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@SuppressWarnings("unchecked") |
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public final V getAndSet(V newValue) { |
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return (V)unsafe.getAndSetObject(this, valueOffset, newValue); |
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} |
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/** |
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* Atomically updates the current value with the results of |
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* applying the given function, returning the previous value. The |
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* function should be side-effect-free, since it may be re-applied |
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* when attempted updates fail due to contention among threads. |
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* |
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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(UnaryOperator<V> updateFunction) { |
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V prev, next; |
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do { |
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prev = get(); |
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next = updateFunction.operate(prev); |
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} while (!compareAndSet(prev, next)); |
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return prev; |
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} |
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/** |
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* Atomically updates the current value with the results of |
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* applying the given function, returning the updated value. The |
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* function should be side-effect-free, since it may be re-applied |
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* when attempted updates fail due to contention among threads. |
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* |
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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(UnaryOperator<V> updateFunction) { |
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V prev, next; |
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do { |
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prev = get(); |
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next = updateFunction.operate(prev); |
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} while (!compareAndSet(prev, next)); |
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return next; |
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} |
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/** |
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* Atomically updates the current value with the results of |
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* applying the given function to the current and given values, |
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* 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. The function |
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* is applied with the current value as its first argument, |
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* and the given update as the second argument. |
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* |
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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(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(); |
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next = accumulatorFunction.operate(prev, x); |
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} while (!compareAndSet(prev, next)); |
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return prev; |
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} |
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/** |
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* Atomically updates the current value with the results of |
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* applying the given function to the current and given values, |
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* 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. The function |
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* is applied with the current value as its first argument, |
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* and the given update as the second argument. |
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* |
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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(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(); |
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next = accumulatorFunction.operate(prev, x); |
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} while (!compareAndSet(prev, next)); |
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return next; |
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} |
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|
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/** |
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* Returns the String representation of the current value. |
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* @return the String representation of the current value |
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*/ |
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public String toString() { |
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return String.valueOf(get()); |
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} |
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} |