/*
* 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.lang.reflect.Array;
import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.function.BinaryOperator;
import java.util.function.UnaryOperator;
/**
* An array of object references in which elements may be updated
* atomically. See the {@link VarHandle} specification for
* descriptions of the properties of atomic accesses.
* @since 1.5
* @author Doug Lea
* @param <E> The base class of elements held in this array
*/
public class AtomicReferenceArray<E> implements java.io.Serializable {
private static final long serialVersionUID = -6209656149925076980L;
private static final VarHandle AA
= MethodHandles.arrayElementVarHandle(Object[].class);
private final Object[] array; // must have exact type Object[]
/**
* Creates a new AtomicReferenceArray of the given length, with all
* elements initially null.
*
* @param length the length of the array
*/
public AtomicReferenceArray(int length) {
array = new Object[length];
}
/**
* Creates a new AtomicReferenceArray with the same length as, and
* all elements copied from, the given array.
*
* @param array the array to copy elements from
* @throws NullPointerException if array is null
*/
public AtomicReferenceArray(E[] array) {
// Visibility guaranteed by final field guarantees
this.array = Arrays.copyOf(array, array.length, Object[].class);
}
/**
* Returns the length of the array.
*
* @return the length of the array
*/
public final int length() {
return array.length;
}
/**
* Returns the current value of the element at index {@code i},
* with memory effects as specified by {@link VarHandle#getVolatile}.
*
* @param i the index
* @return the current value
*/
@SuppressWarnings("unchecked")
public final E get(int i) {
return (E)AA.getVolatile(array, i);
}
/**
* Sets the element at index {@code i} to {@code newValue},
* with memory effects as specified by {@link VarHandle#setVolatile}.
*
* @param i the index
* @param newValue the new value
*/
public final void set(int i, E newValue) {
AA.setVolatile(array, i, newValue);
}
/**
* Sets the element at index {@code i} to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param i the index
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(int i, E newValue) {
AA.setRelease(array, i, newValue);
}
/**
* Atomically sets the element at index {@code i} to {@code
* newValue} and returns the old value,
* with memory effects as specified by {@link VarHandle#getAndSet}.
*
* @param i the index
* @param newValue the new value
* @return the previous value
*/
@SuppressWarnings("unchecked")
public final E getAndSet(int i, E newValue) {
return (E)AA.getAndSet(array, i, newValue);
}
/**
* Atomically sets the element at index {@code i} to {@code newValue}
* if the element's current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#compareAndSet}.
*
* @param i the index
* @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(int i, E expectedValue, E newValue) {
return AA.compareAndSet(array, i, expectedValue, newValue);
}
/**
* Possibly atomically sets the element at index {@code i} to
* {@code newValue} if the element's 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 i the index
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @see #weakCompareAndSetPlain
*/
@Deprecated(since="9")
public final boolean weakCompareAndSet(int i, E expectedValue, E newValue) {
return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);
}
/**
* Possibly atomically sets the element at index {@code i} to
* {@code newValue} if the element's current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
*
* @param i the index
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetPlain(int i, E expectedValue, E newValue) {
return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);
}
/**
* Atomically updates the element at index {@code i} 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 i the index
* @param updateFunction a side-effect-free function
* @return the previous value
* @since 1.8
*/
public final E getAndUpdate(int i, UnaryOperator<E> updateFunction) {
E prev = get(i), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.apply(prev);
if (weakCompareAndSetVolatile(i, prev, next))
return prev;
haveNext = (prev == (prev = get(i)));
}
}
/**
* Atomically updates the element at index {@code i} 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 i the index
* @param updateFunction a side-effect-free function
* @return the updated value
* @since 1.8
*/
public final E updateAndGet(int i, UnaryOperator<E> updateFunction) {
E prev = get(i), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.apply(prev);
if (weakCompareAndSetVolatile(i, prev, next))
return next;
haveNext = (prev == (prev = get(i)));
}
}
/**
* Atomically updates the element at index {@code i} 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 of the element at index {@code i}
* as its first argument, and the given update as the second
* argument.
*
* @param i the index
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the previous value
* @since 1.8
*/
public final E getAndAccumulate(int i, E x,
BinaryOperator<E> accumulatorFunction) {
E prev = get(i), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.apply(prev, x);
if (weakCompareAndSetVolatile(i, prev, next))
return prev;
haveNext = (prev == (prev = get(i)));
}
}
/**
* Atomically updates the element at index {@code i} 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 of the element at index {@code i}
* as its first argument, and the given update as the second
* argument.
*
* @param i the index
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the updated value
* @since 1.8
*/
public final E accumulateAndGet(int i, E x,
BinaryOperator<E> accumulatorFunction) {
E prev = get(i), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.apply(prev, x);
if (weakCompareAndSetVolatile(i, prev, next))
return next;
haveNext = (prev == (prev = get(i)));
}
}
/**
* Returns the String representation of the current values of array.
* @return the String representation of the current values of array
*/
public String toString() {
int iMax = array.length - 1;
if (iMax == -1)
return "[]";
StringBuilder b = new StringBuilder();
b.append('[');
for (int i = 0; ; i++) {
b.append(get(i));
if (i == iMax)
return b.append(']').toString();
b.append(',').append(' ');
}
}
/**
* Reconstitutes the instance from a stream (that is, deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Note: This must be changed if any additional fields are defined
Object a = s.readFields().get("array", null);
if (a == null || !a.getClass().isArray())
throw new java.io.InvalidObjectException("Not array type");
if (a.getClass() != Object[].class)
a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
Field arrayField = java.security.AccessController.doPrivileged(
(java.security.PrivilegedAction<Field>) () -> {
try {
Field f = AtomicReferenceArray.class
.getDeclaredField("array");
f.setAccessible(true);
return f;
} catch (ReflectiveOperationException e) {
throw new Error(e);
}});
try {
arrayField.set(this, a);
} catch (IllegalAccessException e) {
throw new Error(e);
}
}
// jdk9
/**
* Returns the current value of the element at index {@code i},
* with memory semantics of reading as if the variable was declared
* non-{@code volatile}.
*
* @param i the index
* @return the value
* @since 9
*/
public final E getPlain(int i) {
return (E)AA.get(array, i);
}
/**
* Sets the element at index {@code i} to {@code newValue},
* with memory semantics of setting as if the variable was
* declared non-{@code volatile} and non-{@code final}.
*
* @param i the index
* @param newValue the new value
* @since 9
*/
public final void setPlain(int i, E newValue) {
AA.set(array, i, newValue);
}
/**
* Returns the current value of the element at index {@code i},
* with memory effects as specified by {@link VarHandle#getOpaque}.
*
* @param i the index
* @return the value
* @since 9
*/
public final E getOpaque(int i) {
return (E)AA.getOpaque(array, i);
}
/**
* Sets the element at index {@code i} to {@code newValue},
* with memory effects as specified by {@link VarHandle#setOpaque}.
*
* @param i the index
* @param newValue the new value
* @since 9
*/
public final void setOpaque(int i, E newValue) {
AA.setOpaque(array, i, newValue);
}
/**
* Returns the current value of the element at index {@code i},
* with memory effects as specified by {@link VarHandle#getAcquire}.
*
* @param i the index
* @return the value
* @since 9
*/
public final E getAcquire(int i) {
return (E)AA.getAcquire(array, i);
}
/**
* Sets the element at index {@code i} to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param i the index
* @param newValue the new value
* @since 9
*/
public final void setRelease(int i, E newValue) {
AA.setRelease(array, i, newValue);
}
/**
* Atomically sets the element at index {@code i} to {@code newValue}
* if the element's current value, referred to as the <em>witness
* value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchange}.
*
* @param i the index
* @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 E compareAndExchange(int i, E expectedValue, E newValue) {
return (E)AA.compareAndExchange(array, i, expectedValue, newValue);
}
/**
* Atomically sets the element at index {@code i} to {@code newValue}
* if the element's current value, referred to as the <em>witness
* value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeAcquire}.
*
* @param i the index
* @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 E compareAndExchangeAcquire(int i, E expectedValue, E newValue) {
return (E)AA.compareAndExchangeAcquire(array, i, expectedValue, newValue);
}
/**
* Atomically sets the element at index {@code i} to {@code newValue}
* if the element's current value, referred to as the <em>witness
* value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeRelease}.
*
* @param i the index
* @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 E compareAndExchangeRelease(int i, E expectedValue, E newValue) {
return (E)AA.compareAndExchangeRelease(array, i, expectedValue, newValue);
}
/**
* Possibly atomically sets the element at index {@code i} to
* {@code newValue} if the element's current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSet}.
*
* @param i the index
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetVolatile(int i, E expectedValue, E newValue) {
return AA.weakCompareAndSet(array, i, expectedValue, newValue);
}
/**
* Possibly atomically sets the element at index {@code i} to
* {@code newValue} if the element's current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetAcquire}.
*
* @param i the index
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetAcquire(int i, E expectedValue, E newValue) {
return AA.weakCompareAndSetAcquire(array, i, expectedValue, newValue);
}
/**
* Possibly atomically sets the element at index {@code i} to
* {@code newValue} if the element's current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetRelease}.
*
* @param i the index
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetRelease(int i, E expectedValue, E newValue) {
return AA.weakCompareAndSetRelease(array, i, expectedValue, newValue);
}
}