/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
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 *
 * 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);
 }

}