| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent.atomic; |
| |
| import java.lang.invoke.MethodHandles; |
| import java.lang.invoke.VarHandle; |
| import java.util.function.BinaryOperator; |
| import java.util.function.UnaryOperator; |
| |
| /** |
| * An object reference that may be updated atomically. See the {@link |
| * VarHandle} specification for descriptions of the properties of |
| * atomic accesses. |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <V> The type of object referred to by this reference |
| */ |
| public class AtomicReference<V> implements java.io.Serializable { |
| private static final long serialVersionUID = -1848883965231344442L; |
| private static final VarHandle VALUE; |
| static { |
| try { |
| MethodHandles.Lookup l = MethodHandles.lookup(); |
| VALUE = l.findVarHandle(AtomicReference.class, "value", Object.class); |
| } catch (ReflectiveOperationException e) { |
| throw new ExceptionInInitializerError(e); |
| } |
| } |
| |
| private volatile V value; |
| |
| /** |
| * Creates a new AtomicReference with the given initial value. |
| * |
| * @param initialValue the initial value |
| */ |
| public AtomicReference(V initialValue) { |
| value = initialValue; |
| } |
| |
| /** |
| * Creates a new AtomicReference with null initial value. |
| */ |
| public AtomicReference() { |
| } |
| |
| /** |
| * Returns the current value, |
| * with memory effects as specified by {@link VarHandle#getVolatile}. |
| * |
| * @return the current value |
| */ |
| public final V get() { |
| return value; |
| } |
| |
| /** |
| * Sets the value to {@code newValue}, |
| * with memory effects as specified by {@link VarHandle#setVolatile}. |
| * |
| * @param newValue the new value |
| */ |
| public final void set(V newValue) { |
| value = newValue; |
| } |
| |
| /** |
| * Sets the value to {@code newValue}, |
| * with memory effects as specified by {@link VarHandle#setRelease}. |
| * |
| * @param newValue the new value |
| * @since 1.6 |
| */ |
| public final void lazySet(V newValue) { |
| VALUE.setRelease(this, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by {@link VarHandle#compareAndSet}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful. False return indicates that |
| * the actual value was not equal to the expected value. |
| */ |
| public final boolean compareAndSet(V expectedValue, V newValue) { |
| return VALUE.compareAndSet(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Possibly atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}. |
| * |
| * @deprecated This method has plain memory effects but the method |
| * name implies volatile memory effects (see methods such as |
| * {@link #compareAndExchange} and {@link #compareAndSet}). To avoid |
| * confusion over plain or volatile memory effects it is recommended that |
| * the method {@link #weakCompareAndSetPlain} be used instead. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful |
| * @see #weakCompareAndSetPlain |
| */ |
| @Deprecated(since="9") |
| public final boolean weakCompareAndSet(V expectedValue, V newValue) { |
| return VALUE.weakCompareAndSetPlain(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Possibly atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful |
| * @since 9 |
| */ |
| public final boolean weakCompareAndSetPlain(V expectedValue, V newValue) { |
| return VALUE.weakCompareAndSetPlain(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to {@code newValue} and returns the old value, |
| * with memory effects as specified by {@link VarHandle#getAndSet}. |
| * |
| * @param newValue the new value |
| * @return the previous value |
| */ |
| @SuppressWarnings("unchecked") |
| public final V getAndSet(V newValue) { |
| return (V)VALUE.getAndSet(this, newValue); |
| } |
| |
| /** |
| * Atomically updates (with memory effects as specified by {@link |
| * VarHandle#compareAndSet}) the current value with the results of |
| * applying the given function, returning the previous value. The |
| * function should be side-effect-free, since it may be re-applied |
| * when attempted updates fail due to contention among threads. |
| * |
| * @param updateFunction a side-effect-free function |
| * @return the previous value |
| * @since 1.8 |
| */ |
| public final V getAndUpdate(UnaryOperator<V> updateFunction) { |
| V prev = get(), next = null; |
| for (boolean haveNext = false;;) { |
| if (!haveNext) |
| next = updateFunction.apply(prev); |
| if (weakCompareAndSetVolatile(prev, next)) |
| return prev; |
| haveNext = (prev == (prev = get())); |
| } |
| } |
| |
| /** |
| * Atomically updates (with memory effects as specified by {@link |
| * VarHandle#compareAndSet}) the current value with the results of |
| * applying the given function, returning the updated value. The |
| * function should be side-effect-free, since it may be re-applied |
| * when attempted updates fail due to contention among threads. |
| * |
| * @param updateFunction a side-effect-free function |
| * @return the updated value |
| * @since 1.8 |
| */ |
| public final V updateAndGet(UnaryOperator<V> updateFunction) { |
| V prev = get(), next = null; |
| for (boolean haveNext = false;;) { |
| if (!haveNext) |
| next = updateFunction.apply(prev); |
| if (weakCompareAndSetVolatile(prev, next)) |
| return next; |
| haveNext = (prev == (prev = get())); |
| } |
| } |
| |
| /** |
| * Atomically updates (with memory effects as specified by {@link |
| * VarHandle#compareAndSet}) the current value with the results of |
| * applying the given function to the current and given values, |
| * returning the previous value. The function should be |
| * side-effect-free, since it may be re-applied when attempted |
| * updates fail due to contention among threads. The function is |
| * applied with the current value as its first argument, and the |
| * given update as the second argument. |
| * |
| * @param x the update value |
| * @param accumulatorFunction a side-effect-free function of two arguments |
| * @return the previous value |
| * @since 1.8 |
| */ |
| public final V getAndAccumulate(V x, |
| BinaryOperator<V> accumulatorFunction) { |
| V prev = get(), next = null; |
| for (boolean haveNext = false;;) { |
| if (!haveNext) |
| next = accumulatorFunction.apply(prev, x); |
| if (weakCompareAndSetVolatile(prev, next)) |
| return prev; |
| haveNext = (prev == (prev = get())); |
| } |
| } |
| |
| /** |
| * Atomically updates (with memory effects as specified by {@link |
| * VarHandle#compareAndSet}) the current value with the results of |
| * applying the given function to the current and given values, |
| * returning the updated value. The function should be |
| * side-effect-free, since it may be re-applied when attempted |
| * updates fail due to contention among threads. The function is |
| * applied with the current value as its first argument, and the |
| * given update as the second argument. |
| * |
| * @param x the update value |
| * @param accumulatorFunction a side-effect-free function of two arguments |
| * @return the updated value |
| * @since 1.8 |
| */ |
| public final V accumulateAndGet(V x, |
| BinaryOperator<V> accumulatorFunction) { |
| V prev = get(), next = null; |
| for (boolean haveNext = false;;) { |
| if (!haveNext) |
| next = accumulatorFunction.apply(prev, x); |
| if (weakCompareAndSetVolatile(prev, next)) |
| return next; |
| haveNext = (prev == (prev = get())); |
| } |
| } |
| |
| /** |
| * Returns the String representation of the current value. |
| * @return the String representation of the current value |
| */ |
| public String toString() { |
| return String.valueOf(get()); |
| } |
| |
| // jdk9 |
| |
| /** |
| * Returns the current value, with memory semantics of reading as |
| * if the variable was declared non-{@code volatile}. |
| * |
| * @return the value |
| * @since 9 |
| */ |
| public final V getPlain() { |
| return (V)VALUE.get(this); |
| } |
| |
| /** |
| * Sets the value to {@code newValue}, with memory semantics |
| * of setting as if the variable was declared non-{@code volatile} |
| * and non-{@code final}. |
| * |
| * @param newValue the new value |
| * @since 9 |
| */ |
| public final void setPlain(V newValue) { |
| VALUE.set(this, newValue); |
| } |
| |
| /** |
| * Returns the current value, |
| * with memory effects as specified by {@link VarHandle#getOpaque}. |
| * |
| * @return the value |
| * @since 9 |
| */ |
| public final V getOpaque() { |
| return (V)VALUE.getOpaque(this); |
| } |
| |
| /** |
| * Sets the value to {@code newValue}, |
| * with memory effects as specified by {@link VarHandle#setOpaque}. |
| * |
| * @param newValue the new value |
| * @since 9 |
| */ |
| public final void setOpaque(V newValue) { |
| VALUE.setOpaque(this, newValue); |
| } |
| |
| /** |
| * Returns the current value, |
| * with memory effects as specified by {@link VarHandle#getAcquire}. |
| * |
| * @return the value |
| * @since 9 |
| */ |
| public final V getAcquire() { |
| return (V)VALUE.getAcquire(this); |
| } |
| |
| /** |
| * Sets the value to {@code newValue}, |
| * with memory effects as specified by {@link VarHandle#setRelease}. |
| * |
| * @param newValue the new value |
| * @since 9 |
| */ |
| public final void setRelease(V newValue) { |
| VALUE.setRelease(this, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to {@code newValue} if the current value, |
| * referred to as the <em>witness value</em>, {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#compareAndExchange}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return the witness value, which will be the same as the |
| * expected value if successful |
| * @since 9 |
| */ |
| public final V compareAndExchange(V expectedValue, V newValue) { |
| return (V)VALUE.compareAndExchange(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to {@code newValue} if the current value, |
| * referred to as the <em>witness value</em>, {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#compareAndExchangeAcquire}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return the witness value, which will be the same as the |
| * expected value if successful |
| * @since 9 |
| */ |
| public final V compareAndExchangeAcquire(V expectedValue, V newValue) { |
| return (V)VALUE.compareAndExchangeAcquire(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to {@code newValue} if the current value, |
| * referred to as the <em>witness value</em>, {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#compareAndExchangeRelease}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return the witness value, which will be the same as the |
| * expected value if successful |
| * @since 9 |
| */ |
| public final V compareAndExchangeRelease(V expectedValue, V newValue) { |
| return (V)VALUE.compareAndExchangeRelease(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Possibly atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#weakCompareAndSet}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful |
| * @since 9 |
| */ |
| public final boolean weakCompareAndSetVolatile(V expectedValue, V newValue) { |
| return VALUE.weakCompareAndSet(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Possibly atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#weakCompareAndSetAcquire}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful |
| * @since 9 |
| */ |
| public final boolean weakCompareAndSetAcquire(V expectedValue, V newValue) { |
| return VALUE.weakCompareAndSetAcquire(this, expectedValue, newValue); |
| } |
| |
| /** |
| * Possibly atomically sets the value to {@code newValue} |
| * if the current value {@code == expectedValue}, |
| * with memory effects as specified by |
| * {@link VarHandle#weakCompareAndSetRelease}. |
| * |
| * @param expectedValue the expected value |
| * @param newValue the new value |
| * @return {@code true} if successful |
| * @since 9 |
| */ |
| public final boolean weakCompareAndSetRelease(V expectedValue, V newValue) { |
| return VALUE.weakCompareAndSetRelease(this, expectedValue, newValue); |
| } |
| |
| } |
